Counting Sheep: The Science and Pleasures of Sleep and Dreams
Counting Sheep: The Science and Pleasures of Sleep and Dreams
Paul Martin
A brilliant overview of that most vital, most underrated and most elusive of human activities, sleep.Using the approach and skills he deployed to such successful effect on the relationship between mind and body in the prize-winning ‘The Sickening Mind’, likeable British popular science author Paul Martin here tackles the science of that most mysterious, elusive and alluring of human activities, sleeping, and draws on both cutting-edge neuroscience and classic literature to do so.We spend one third of our lives asleep, but know hardly anything about it, and can remember so little of it as we come out of it. Why?Are dreams the place we go to resolve our problems, emasculate our fears and rehearse our hopes? Why are we paralysed when we dream? Why did sleep evolve?And is anybody getting enough sleep?
COUNTING SHEEP
The Science and Pleasures of Sleep and Dreams
PAUL MARTIN
Copyright (#ulink_3520a952-75a8-598d-ac67-5a97b134707f)
William Collins
An imprint of HarperCollinsPublishers 1 London Bridge Street London SE1 9GF
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Published by HarperPress 2003
First published in Great Britain by HarperCollinsPublishers 2002
Copyright © Paul Martin 2002
Paul Martin asserts the moral right to be identified as the author of this work
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Source ISBN: 9780006551720
Ebook Edition © MARCH 2016 ISBN: 9780007406784
Version: 2016-02-11
Contents
Cover (#ua80fc455-2f27-5d7c-9fca-eb9476ae9cb0)
Title Page (#u9107714d-ed60-510f-8976-9b68940ee021)
Copyright (#u8bab2137-8c70-51b4-aad3-c41332c36563)
PART I: PRELIMINARIES (#u534b858d-4b59-5aa3-ab51-070d7768eea6)
1: A Third of Life (#uc050b292-b7ef-520d-9723-b15099ecb4b3)
A sleep-sick society? (#ulink_e2384876-eacb-5ddd-8084-65fbf35183ed)
The universal imperative (#ulink_ed620ba9-9745-5479-9f07-85a8ec6715f3)
Half asleep (#ulink_08143b2d-cd18-50f8-ad75-388778404476)
Nice, not naughty (#ulink_c0444367-682c-53a6-89e9-a12457fba012)
PART II: INSUFFICIENCIES (#ub710fa96-b025-54af-bf3b-5b7d70b3a5a7)
2: Sleepy People (#u85dea0be-480b-570b-aad0-925a575e8049)
Are we sleep-deprived? (#ulink_fe5a0cad-4d97-5b63-a7bb-d9cf7daea491)
Are you sleep-deprived? (#ulink_4147fc1b-77dd-5d2f-9ba6-ab5571ad6dd1)
Reasons for not sleeping (#ulink_d08c104c-673c-54bf-87e4-56c1369891c4)
Ancient and modern (#ulink_e73b743e-63df-5856-a4d6-90093cd1dd70)
Sleepy drivers (#ulink_0643902d-ddb4-5187-8819-0cd9e711ee35)
Sleepy pilots (#ulink_838729e3-6261-5c3b-9997-d00f25214ee1)
Sleepy doctors (#ulink_36b6e00e-5b16-5e6f-9770-a2d0c6b82975)
The madness of politicians (#ulink_6cc25b44-5507-554b-aca7-673fc0d8e902)
Truly, madly, sleepily (#ulink_9d6ee05c-2417-52dd-8ea8-2302adb003cf)
The price of eternal vigilance is liberty (#ulink_69da4085-2e99-5364-b785-5c1b1f2d4f65)
3: Dead Tired (#u30b7ddb6-7431-5612-b355-a029da480b32)
Sleepiness (#ulink_81fa281f-3984-51f4-b95c-dedd4680d9fe)
Fighting the beast (#ulink_46a4edee-a805-5e7f-8889-4f3c6107acdb)
A soil for peevishness (#ulink_35a0e7d1-d74a-5bfe-a66b-b06123da7134)
Tired people are stupid and reckless (#ulink_ef3870d3-3db6-5d18-b4b7-60db998cfccc)
Alcohol, beauty and old age (#ulink_a02e9f05-03d5-5079-b204-3bf3edf53a1d)
Champion wakers (#ulink_75db5262-c5f6-5a34-878a-5723c74b53a2)
Uses and abuses (#ulink_1d3af885-9d46-5d54-ae0b-38ea58ba6325)
4: The Golden Chain (#uffe99068-ecfa-5859-a988-74273041693f)
A waking death (#ulink_6754d5e1-dc33-521d-b290-ac9245933eaf)
Body and soul (#ulink_4dda6a11-388e-5383-bff7-d610f33294aa)
Sleep, immunity and health (#ulink_f4684fd9-9e90-50a3-9042-3bedd31d071d)
The Battle of Stalingrad (#ulink_447371da-4d9c-5f24-ac9a-04c82ed1406c)
Sleepless in hospital (#ulink_706213d3-ec7d-53b4-80e6-565c0cf5b4e3)
PART III: MECHANISMS (#uac3c47f7-b4f2-5ea4-9c81-15fc01e5a6e9)
5: The Shapes of Sleep (#u39a528ce-bde6-5898-a17d-f15c306aec06)
Measuring sleep (#ulink_d9d736a1-548b-542b-9ac6-6d7ca5da5a06)
Falling asleep again, what am I to do? (#ulink_6b3ede10-1c7a-5e9b-8fe7-0cedc375b51f)
The sleep cycle (#ulink_82872f29-2e72-5581-8be5-eabbd536e4ab)
The paradoxical world of REM (#litres_trial_promo)
The sleep cycle continued (#litres_trial_promo)
Waking up (#litres_trial_promo)
The quality of sleep (#litres_trial_promo)
Meditating – or only sleeping? (#litres_trial_promo)
6: Morpheus Undressed (#litres_trial_promo)
The rhythms of life (#litres_trial_promo)
So SAD (#litres_trial_promo)
Larks and owls (#litres_trial_promo)
Genes and sleep (#litres_trial_promo)
A sleeplessness that kills (#litres_trial_promo)
7: Strange Tales of Erections and Yawning (#litres_trial_promo)
Nocturnal erections (#litres_trial_promo)
The mystery of yawning (#litres_trial_promo)
8: Friends and Enemies of Sleep (#litres_trial_promo)
Brother caffeine (#litres_trial_promo)
Sister alcohol (#litres_trial_promo)
Tobacco (#litres_trial_promo)
Food for sleep (#litres_trial_promo)
Exercise is bunk, isn’t it? (#litres_trial_promo)
Things that go bump in the night (#litres_trial_promo)
Shift work (#litres_trial_promo)
Poppy, mandragora and drowsy syrups (#litres_trial_promo)
Hypnotic exotica (#litres_trial_promo)
PART IV: DREAMS (#litres_trial_promo)
9: The Children of an Idle Brain? (#litres_trial_promo)
To sleep, perchance … (#litres_trial_promo)
Do flies dream? (#litres_trial_promo)
A dream within a dream? (#litres_trial_promo)
Dreaming as madness (#litres_trial_promo)
Are dreams meaningful? (#litres_trial_promo)
Like wine through water (#litres_trial_promo)
Can dreams be sinful? (#litres_trial_promo)
10: A Second Life (#litres_trial_promo)
A creative state (#litres_trial_promo)
Stevenson’s Brownies (#litres_trial_promo)
Lucid dreams (#litres_trial_promo)
The great dreamer (#litres_trial_promo)
PART V: ORIGINS (#litres_trial_promo)
11: From Egg to Grave (#litres_trial_promo)
Screaming babies (#litres_trial_promo)
Bad children (#litres_trial_promo)
Yawning youth (#litres_trial_promo)
Old and grey and full of sleep (#litres_trial_promo)
12: The Reason of Sleep (#litres_trial_promo)
The evolution of sleep (#litres_trial_promo)
What is sleep for? (#litres_trial_promo)
What is REM sleep for? (#litres_trial_promo)
Reverse learning (#litres_trial_promo)
To sleep, perchance to learn (#litres_trial_promo)
Should machines sleep? (#litres_trial_promo)
PART VI: PROBLEMS (#litres_trial_promo)
13: Bad Sleepers (#litres_trial_promo)
An intolerable lucidity (#litres_trial_promo)
Why can’t you sleep? (#litres_trial_promo)
Storm and stress and sleep (#litres_trial_promo)
What to do? (#litres_trial_promo)
Staying awake (#litres_trial_promo)
14: Dark Night (#litres_trial_promo)
Walking and talking (#litres_trial_promo)
Nightmares, night terrors, sleep paralysis and the Old Hag (#litres_trial_promo)
Moving sleep (#litres_trial_promo)
Midnight feasting (#litres_trial_promo)
Soggy sheets (#litres_trial_promo)
Aching heads (#litres_trial_promo)
Troubled guts (#litres_trial_promo)
Troubled minds (#litres_trial_promo)
Sudden nocturnal death (#litres_trial_promo)
Narcolepsy (#litres_trial_promo)
15: Pickwickian Problems (#litres_trial_promo)
The wonderful world of snoring (#litres_trial_promo)
Silence is golden (#litres_trial_promo)
Breathless in bed (#litres_trial_promo)
Consequences – mostly dire (#litres_trial_promo)
Unblocking those tubes (#litres_trial_promo)
PART VII: PLEASURES (#litres_trial_promo)
16: And So to Bed (#litres_trial_promo)
A brief history of beds (#litres_trial_promo)
Sleeping partners (#litres_trial_promo)
17: An Excellent Thing (#litres_trial_promo)
Puritans and hypocrites (#litres_trial_promo)
Naps, nappers and napping (#litres_trial_promo)
Sweet dreams (#litres_trial_promo)
Blessed oblivion (#litres_trial_promo)
Give sleep a chance (#litres_trial_promo)
In praise of horizontalism (#litres_trial_promo)
Keep Reading (#litres_trial_promo)
References (#litres_trial_promo)
Index (#litres_trial_promo)
Acknowledgements (#litres_trial_promo)
About the Author (#litres_trial_promo)
Praise (#litres_trial_promo)
Also by the Author (#litres_trial_promo)
About the Publisher (#litres_trial_promo)
PART I Preliminaries (#ulink_d19660b1-89c0-5a86-8526-91b26e8f214f)
1 A Third of Life (#ulink_31cf6e27-a8e6-5a49-86cd-f1af9fe822b4)
Man … consumes more than one third of his life in this his irrational situation.
Erasmus Darwin, Zoonomia (1801)
Sleep: a state so familiar yet so strange. It is the single most common form of human behaviour and you will spend a third of your life doing it – 25 years or more, all being well. When you die, a bigger slice of your existence will have passed in that state than in making love, raising children, eating, playing games, listening to music, or any of those other activities that humanity values so highly.
Sleep is a form of behaviour, just as eating or socialising or fighting or copulating are forms of behaviour, even if it is not the most gripping to observe. Most of the action goes on inside the brain. It is also a uniquely private experience, even when sharing a bed. When we are awake we all inhabit a common world, but when we sleep each of us occupies a world of our own. Most of us, however, have precious little awareness of what we experience in that state. Our memories of sleeping and dreaming mostly evaporate when we awake, erasing the record every morning.
Many of us do not get enough sleep and we suffer the consequences, often without realising what we are doing to ourselves. The demands of the 24-hour society are marginalising sleep, yet it is not an optional activity. Nature imposes it upon us. We can survive for longer without food. When our sleep falls short in quantity or quality we pay a heavy price in depressed mood, impaired performance, damaged social relationships and poorer health. But we usually blame something else.
Sleep is an active state, generated within the brain, not a mere absence of consciousness. You are physiologically capable of sleeping with your eyelids held open by sticking plaster, bright lights flashing in your eyes and loud music playing in your ears. We shall later see how science has revealed the ferment of electrical and chemical activity that goes on inside the brain during sleep, and how the sleeping brain operates in a quite different mode from waking consciousness. We shall see too how lack of sleep erodes our quality of life and performance while simultaneously making us more vulnerable to injuries and illness. Science amply supports William Shakespeare’s view that sleep is the ‘chief nourisher in life’s feast’.
What is sleep and what is it for? Why do so many people have such problems with it? Why do we dream? Although sleep forms a central strand of human and animal life it is still poorly understood and widely neglected. It is an inglorious example of familiarity breeding contempt. Sleep is so much a part of our everyday existence that we take it for granted. We are ignorant even of our ignorance. In 1758, Doctor Samuel Johnson summed it up like this:
Among the innumerable mortifications that waylay human arrogance on every side may well be reckoned our ignorance of the most common objects and effects … Vulgar and inactive minds confound familiarity with knowledge, and conceive themselves informed of the whole nature of things when they are shown their form or told their use … Sleep is a state in which a great part of every life is passed. No animal has been yet discovered whose existence is not varied with intervals of insensibility. Yet of this change so frequent, so great, so general, and so necessary, no searcher has yet found either the efficient or final cause; or can tell by what power the mind and body are thus chained down in irresistible stupefaction; or what benefits the animal receives from this alternate suspension of its active powers.
The scientists who do know something about sleep often bemoan society’s ignorance of it. They point to the vast gap between current scientific understanding of sleep, patchy though it is, and the practical benefits it could bring if that knowledge were absorbed and acted upon by society. Our collective indifference towards sleep has enormous and largely avoidable costs.
A sleep-sick society? (#ulink_2011d958-bc4c-5573-9ede-d62f2c781ff1)
The mere presence of an alarm clock implies sleep deprivation, and what bedroom lacks an alarm clock?
James Gleick, Faster (1999)
All is not well with the state of sleep. Many of us depend on an alarm clock to prise us out of bed each morning, and children’s bedrooms increasingly resemble places of entertainment rather than places of sleep. When given the opportunity, we sleep in at the weekends and feel only half awake when we do get up. On that long-awaited holiday we find the change of scenery (or is it the air?) makes us even sleepier. We are told that lying around and sleeping too much will only make us sleepier. But in truth we feel sleepy at weekends and on holidays not because we are sleeping too much, but because we have slept too little the rest of the time.
A century ago the majority toiled long hours while the affluent few idled away their time. Today, however, the more conventionally successful you are, the less free time you will probably have. Having nothing to do is seen as a sign of worthlessness, while ceaseless activity signifies status and success. Supposedly unproductive activities are deprioritised or delegated. And according to prevailing cultural attitudes, sleeping is one of the least productive of all human activities – more worthwhile perhaps than sitting around picking your nose, but not much. In their ceaseless pursuit of work and pleasure the cash-rich buy time from others, hiring them to clean their houses, look after their children and cook their food. But one of the activities you simply cannot delegate to anyone else is sleeping.
Evolution equipped humans, in common with all other animals, with biological mechanisms to make us sleep at roughly the same time every day. However, those mechanisms evolved to cope with a pre-industrial world that was vastly different from the one we now inhabit.
Our daily cycles of sleep and activity are no longer driven by dawn and dusk, but by clocks, electric lighting and work schedules. Sleep has become increasingly devalued in the 24-hour society. Many regard sleep as wasted time and would prefer to sacrifice less of their busy lives to it. We live in a world where there are too many tired, sleep-deprived people. Think of those pinched, yawning faces you can see every day on the trains and in buses and in cars crawling through jams. They look as if they have been brainwashed, but they are just tired.
We pay a steep price for neglecting sleep, in our ignorance and indifference. The scientific evidence tells us that far too many people in industrialised societies are chronically sleep-deprived, with damaging consequences for their mental and physical health, performance at work, quality of life and personal relationships. William Dement, a pioneering scientist in the field, believes that we now live in a ‘sleep-sick society’. Scientists have not yet reached a consensus about the precise extent of sleep deprivation in society, but they do all agree that sleepiness is a major cause of accidents and injuries. In fact, sleepiness is responsible for far more deaths on the roads than alcohol or drugs.
Everyone has heard about the need for a balanced diet and physical exercise, even if many of us fail to follow the advice. But sleep is lost in a deep well of ignorance and apathy. Even the medical profession pays it scant regard. Sleep and its disorders barely feature in the teaching of medicine, and few physicians are fully equipped to deal with the sleep problems they regularly encounter. When researchers from Oxford University investigated British medical education in the late 1990s, they discovered that the average amount of time devoted to sleep and sleep disorders in undergraduate teaching was five minutes, rising to a princely peak of 15 minutes in preclinical training. Your doctor is therefore unlikely to be an expert on the subject.
The general public and the medical profession are not the only ones to display a remarkable indifference to sleep. So too do most contemporary writers. Considering that sleep accounts for a third of human existence, it features remarkably rarely in novels, biographies, social histories or learned texts on neurobiology, psychology and medicine. And the few accounts that have made it into print are mostly concerned with what happens when it goes wrong. Insomnia and nightmares loom large in the tiny literature of sleep.
Few biographies mention the sleep behaviour or dreams of their subjects. That part of their story is almost invariably missing, as if somehow we all cease to exist at night. And most of those scholarly books that set out to explain how the human mind works say little or nothing about what goes on during the several hours of every day when the mind is sleeping and dreaming. They are really just books about how the brain works when it is awake. Our neglect of sleep is underlined by its absence from our literature.
Vladimir Nabokov once said that all the great writers have good eyes. What has happened to the eyes of writers as far as sleep and dreams are concerned? It was not always so. Older literature is distinctly richer in references to sleeping and dreaming, perhaps because darkness and sleep and dreams were much more prominent aspects of everyday life before the invention of the electric light bulb and the advent of the 24-hour society. Shakespeare’s works are thick with allusions to sleep and dreams, as are Dickens’s. We shall encounter some of them later. Meanwhile, to set the right tone, here is Sancho Panza’s eulogy to sleep from Don Quixote:
God bless the inventor of sleep, the cloak that covers all man’s thoughts, the food that cures all hunger, the water that quenches all thirst, the fire that warms the cold, the cold that cools the heat; the common coin, in short, that can purchase all things, the balancing weight that levels the shepherd with the king and the simple with the wise.
The universal imperative (#ulink_3acf04c4-0b0c-541e-974a-051f57e446a0)
Almost all other animals are observed to partake of sleep, aquatic, winged, and terrestrial creatures alike. For every kind of fish and the soft-shelled species have been seen sleeping, as has every other creature that has eyes.
Aristotle (384–322 BC), On Sleep and Waking
Sleep is a universal human characteristic, like eating and drinking. Absolutely everybody does it. Sleep occupies about one third of each human life, and up to two thirds of a baby’s time. (According to Groucho Marx, the proportion rises to three thirds if you live in Peoria.) It is a common bond that ties us all together. We have no choice: the longer we go without sleep, the stronger our desire for it grows. Tiredness, like hunger and thirst, will eventually force us to do the right thing whether we want to or not.
The dreams that accompany sleep are equally ubiquitous features of human life, even if many of us retain little memory of them after we awake. Dreaming is a classless activity that unites monarchs and paupers, a thought that Charles Dickens mused upon in one of his essays:
Here, for example, is her Majesty Queen Victoria in her palace, this present blessed night, and here is Winking Charley, a sturdy vagrant, in one of her Majesty’s jails … It is probable that we have all three committed murders and hidden bodies. It is pretty certain that we have all desperately wanted to cry out, and have had no voice; that we have all gone to the play and not been able to get in; that we have all dreamed much more of our youth than of our later lives.
Sleep is not a specifically human trait, of course. On the contrary, it is a universal characteristic of complex living organisms, as Aristotle deduced more than 23 centuries ago. Sleep is observed in animals of every sort, including insects, molluscs, fish, amphibians, birds and mammals. Within the animal world, sleep does vary enormously in quantity, quality and timing, accounting for anything up to 80 per cent of some animals’ lifespans. But they all do it, one way or another. Some species, especially predators, spend more of their lives asleep than they do awake, a fact that TV documentaries and natural-history books seldom mention.
How do we know that an animal is sleeping? It is hard enough sometimes to be sure that a human is asleep, let alone a fish or a fly. The ultimate indicator of whether an animal or person is asleep is the distinctive pattern of electrical activity in its brain. During deep sleep the billions of individual nerve cells in the brain synchronise their electrical activity to some extent, generating characteristic waves of tiny voltage changes that can be detected by electrodes placed on the scalp. We shall be exploring the nature and internal structure of sleep later. The easiest way to recognise sleep, however, is from overt behaviour.
Sleep has several rather obvious distinguishing characteristics. A sleeping person or animal will generally remain in the same place for a prolonged period, perhaps several hours. There will be a certain amount of twitching, shifting of posture and fidgeting. Young animals will suckle while they sleep and ruminants will carry on chewing the cud. But sleepers normally do not get up and change their location. (When they do, we recognise it as a curious phenomenon and call it sleepwalking.)
Sleeping organisms also adopt a characteristic posture. Sloths and bats, for example, sleep hanging upside down from a branch. The Mediterranean flour moth sleeps with its antennae swivelled backwards and the tips tucked under its wings. If you are careful, you can gently lift the sleeping moth’s wing without disturbing it – a trick that will definitely not work when it is awake. A lizard will settle on a branch during the hours before sunset, curl up its tail, close its eyelids, retract its eyeballs and remain in that distinctly sleep-like posture all night unless it is disturbed. A partridge, like many birds, will rest its weight on one leg while it sleeps. It is said that some gourmets can tell which leg, from its taste.
Monkeys and apes, including humans, usually sleep lying down. Indeed, we are built in such a way that we find it difficult to sleep properly unless we are lying down. People can and sometimes do sleep after a fashion while sitting, notably in aeroplanes, business meetings and school classrooms. If you are really exhausted, you might even manage to snatch some sleep standing up. But sleep taken while standing or sitting upright is generally fitful, shallow and unrefreshing. The non-horizontal sleeper may repeatedly nod off, but as soon as they descend beyond the shallowest stages of sleep their muscles relax, they begin to sway and their brain wakes them up again. That is why we ‘nod off’. If you travel frequently on trains or buses, you might have had the dubious pleasure of sitting next to a weary commuter who has nodded off all over your shoulder. Recordings of brain-wave patterns show that people sleeping in an upright sitting position achieve only the initial stages of light sleep, not the sustained, deep sleep we require to wake up feeling truly refreshed. The reason is simple. Our muscles relax when we are fully asleep and we would fall over if we were not already lying down. Our brains therefore do not permit us to enter sustained, deep sleep unless we are in a physically stable, horizontal (or near-horizontal) posture.
Despite the virtual impossibility of sleeping deeply while sitting upright, we are sometimes forced to try. In Down and Out in Paris and London, George Orwell describes a particularly unwelcoming form of overnight accommodation that was known to the homeless of prewar London as the Twopenny Hangover. At the Twopenny Hangover the night’s residents would sit in a row along a bench. In front of them was a rope, and the would-be sleepers would lean on this rope as though leaning over a fence. In that posture they were supposed to sleep. At five o’clock the next morning an official, wittily known as the valet, would cut the rope so that the residents could begin another day of wandering the streets.
Nowadays, tourist-class airline passengers travelling long distances can enjoy an experience similar to the Twopenny Hangover, albeit at vastly greater expense. George Orwell’s autobiographical account of grinding poverty in the late 1920s is also a sharp reminder that lack of money is often accompanied by lack of decent sleep. Rough sleepers rarely get a good night’s sleep.
Sleep has several other distinctive characteristics besides immobility and posture. In many species, including humans, individuals return to the same place each night (or each day, if they are nocturnal) in order to sleep. More generally, all members of a given species will tend to choose the same sorts of sleeping places. The distinctive feature of those places is often their security. Birds usually sleep on inaccessible branches or ledges. Many small mammals sleep in underground burrows where they are safer from predators. Fishes lie on the bottom, or wedge themselves into a crevice or against the underside of a rock. We humans prefer to sleep in relatively private and secure places. Given the choice, we rarely opt to sleep on busy streets or in crowded restaurants.
One obvious feature of sleep is a marked reduction in responsiveness to sights, sounds and other sensory stimuli. To provoke a response from a sleeping organism, stimuli have to be more intense or more relevant to the individual. For example, the reef fish known as the slippery dick sleeps during the hours of darkness, partly buried in the sand. While it is in this state, the sleeping slippery dick can be gently lifted to the surface by hand without it waking up and swimming off.
A sort of perceptual wall is erected during sleep, insulating the mind from the outside world. You would still be able to sleep if you had no eyelids, because your sleeping brain would not register what your eyes could see. This sensory isolation is highly selective, however. You can sleep through relatively loud noises from traffic or a radio, but a quiet mention of your name can rouse you immediately. Your brain is not simply blocked off during sleep. Moreover, this reduced responsiveness is rapidly reversible – a characteristic that distinguishes sleep from states such as unconsciousness, coma, anaesthesia and hibernation. A suitable stimulus, particularly one signifying immediate danger, can snap a sleeping person into staring-eyed alertness in an instant.
Another diagnostic feature of sleep is its regular cycle of waxing and waning. Living organisms sleep and wake according to a regular 24-hour cycle, or circadian rhythm. All members of a given species tend to sleep during the same part of the 24-hour cycle, when their environment is least favourable for other activities such as looking for food. For most species this means sleeping during the hours of darkness, but some species do the reverse. Many small mammals, which would be more vulnerable to predators during daylight, sleep by day and forage at night. Aside from a few nocturnal specialists such as owls, birds cannot easily fly in the dark, and most reptiles find it hard to maintain a sufficiently high body temperature to be active during the cool of night. Most birds and reptiles therefore sleep at night. Predators tend to sleep when their prey are asleep and hunt when their prey are up and about.
Sleep, then, is characterised by a special sleeping place and posture, prolonged immobility, a selective and rapidly reversible reduction in responsiveness to stimuli, and a 24-hour cycle. According to these and other criteria, all mammals, birds, fish, amphibians, reptiles and insects that have been inspected have been found to sleep.
Take the humble fruit fly, Drosophila melanogaster, for example. This small insect displays all the key features of sleep, and more. Fruit flies alternate between periods of activity and rest according to a 24-hour cycle. They go to sleep in a preferred location where they remain immobile for two hours or more at a time, usually at around the same time of day. While they are asleep, they are much less reactive to sights, sounds and other sensory stimuli. If they are prevented from sleeping they show an increasing propensity to sleep. And when they do sleep after a period of deprivation, they are harder to wake up and they sleep for longer, as if catching up. Young fruit flies sleep more than old fruit flies, just as babies sleep more than adult humans. And, also like humans, their sleep is assisted by sleep-inducing drugs and disrupted by stimulants such as caffeine.
Many small mammals spend more than half their lives asleep. Think of the dormouse, for example. Lewis Carroll’s description in Alice’s Adventures in Wonderland is biologically authentic, apart from the animals’ ability to talk grammatical English:
There was a table set out under a tree in front of the house, and the March Hare and the Hatter were having tea at it: a Dormouse was sitting between them, fast asleep, and the other two were resting their elbows on it, and talking over its head. ‘Very uncomfortable for the Dormouse,’ thought Alice; ‘only, as it’s asleep, I suppose it doesn’t mind’…
‘You might just as well say that “I see what I eat” is the same thing as “I eat what I see”!’
‘You might just as well say,’ added the March Hare, that “I like what I get” is the same thing as “I get what I like”!’
‘You might just as well say,’ added the Dormouse, who seemed to be talking in his sleep, ‘that “I breathe when I sleep” is the same thing as “I sleep when I breathe”!’
‘It is the same thing with you,’ said the Hatter.
Dormice (which actually comprise 20 different species of nocturnal rodents) really do spend most of their time asleep, as do many other species of small mammals. The volcano mouse spends more than 17 hours a day asleep. Even the naked mole rat devotes 12 hours a day to sleep, despite the fact that it lives underground and has become so adapted to subterranean life that it has lost the power of sight.
The champion sleepers are two-toed sloths, which dedicate an average of 20 hours a day, or more than 80 per cent of their entire lives, to sleep. (Whereas three-toed sloths are much livelier, sleeping for a mere 17 hours a day.) Close behind come armadillos, opossums and some species of bats, which sleep for 18–19 hours a day. Many lizards spend more than 16 hours a day in sleep. Nearer to home, cats, rats, mice and hamsters sleep for 13–14 hours a day. Birds too can be great sleepers, although their sleep is less obvious to the casual observer because it is fragmented into short episodes. Starlings, which are fairly typical, spend a total of more than nine hours a day asleep, but this is split into many short bouts, each lasting on average only seven minutes. At the other end of the sleep spectrum lurk the wakeful grazers – cows, goats, elephants, donkeys, horses, sheep, deer and giraffes – all surviving on a meagre ration of three or four hours a day. But that is the minimum.
We humans occupy the low-to-middle ground of the zoological sleep spectrum, along with moles – or, at least, we do if we assign ourselves the proverbial eight hours a night. In reality, most people get substantially less than eight hours – a theme we shall be exploring in the next three chapters. On that same theme, it is notable that our closest biological relatives, the apes and monkeys, sleep more than us. Chimpanzees, rhesus monkeys, squirrel monkeys, vervets, patas monkeys and baboons sleep nine or ten hours a night, while the gorilla averages 12 hours. The sleepiest primate is the owl monkey, which clocks up 17 hours a day of sleep, accounting for more than 70 per cent of its life.
Do plants sleep? This is almost, but not quite, as stupid a question as it may seem. In one loose and misleading sense plants do display some behavioural characteristics of sleep. Many plants alter their shape each night, as though curling up to go to sleep. Some species furl their leaves like an umbrella, some allow their leaves to droop as if they need watering, while others, including lettuces and radishes, point their leaves vertically upwards. They all display a distinct 24-hour circadian rhythm.
Pliny the Elder noted this ‘sleep of plants’ in the first century AD. Eighteen centuries later, Charles Darwin investigated the ‘sleep of plants’ with a series of ingenious experiments in the garden of his home at Down House in Kent. Darwin was confident that the phenomenon was not true sleep. ‘Hardly any one,’ he wrote, ‘supposes that there is really any analogy between the sleep of animals and that of plants.’ As usual, Darwin was right. His experiments demonstrated that plants alter their shape at night to protect themselves from their physical environment. He found, for example, that if he left a plant outside at night, with its leaves tied up to prevent them from drooping, the result was a blackened, shrivelled and dead plant the next morning. Darwin also discovered that a plant will not ‘sleep’ if it is shaken violently.
Half asleep (#ulink_f6c0db3f-e53f-5b4f-8023-863d7fec0ad1)
And the small fowl are making melody
That sleep away the night with open eye
Geoffrey Chaucer, Prologue to The Canterbury Tales (c. 1387)
Sleep is such an overriding biological imperative that evolution has found ingenious ways of enabling animals to do it in the face of formidable obstacles. Nature, it seems, will do almost anything to ensure that animals sleep.
Consider dolphins, for example. They are air-breathing mammals like us, so they must swim to the surface each time they want to take a breath. They would drown if they fell into deep sleep while deep underwater. One possible solution to this biological design conundrum would be to wake up each time a breath of air was required. However, evolution has produced a more elegant solution: only one half of the dolphin’s brain goes to sleep at a time.
Dolphins are capable of what is known as unihemispheric sleep, in which one hemisphere of the brain submerges into deep sleep while the other hemisphere remains awake. The two halves of the brain take it in turns to sleep, swapping at intervals of between one and three hours. This cerebral juggling trick enables dolphins to sleep underwater without drowning, which is just as well considering that they spend a good third of their lives asleep. Unihemispheric sleep has been recorded in several species of dolphins, porpoises and whales, including bottlenosed and Amazonian dolphins, Black Sea porpoises and white whales.
Despite the apparent convenience of being able to sleep and stay awake simultaneously, very few mammals are capable of unihemispheric sleep. The biological benefits of sleeping with only half of the brain at a time presumably outweigh the disadvantages only under unusual conditions, such as those encountered by air-breathing mammals living in the deep oceans.
Unihemispheric sleep is widespread in birds, however. They do it for a. different biological reason. Sleeping with half the brain awake and one eye open allows them to sleep while simultaneously remaining vigilant for predators. In birds, each eye exclusively feeds the visual processing areas in the opposite half of the brain: thus, all the nerve fibres coming from the right eye connect to the left hemisphere of the brain and vice versa. When a bird is in unihemispheric sleep its open eye is the one corresponding to the waking half of the brain, while the closed eye is connected to the sleeping half. If a bird feels relatively safe, it closes both eyes, and both sides of its brain go to sleep.
An experiment with mallard ducks demonstrated how unihemispheric sleep helps birds to stay safe from predators. Four ducks were placed in a row along a perch, the idea being that the ducks at either end of the row would feel more vulnerable to predators than the two in the middle. In the natural world it is generally a bad idea to be on the edge of a group if you might end up as some other animal’s dinner. As predicted, video recordings showed that the outer two birds were much more likely to sleep with one eye open than the two on the inside; their unihemispheric sleep increased by 150 per cent. The amount of unihemispheric sleep rose further when the ducks were shown frightening video images of an approaching predator.
The relationship between unihemispheric sleep and vigilance was finely controlled. The exposed birds on the ends of the row preferentially opened their outward-facing eye – the one directed towards potential danger. From time to time, a bird would turn round and switch eyes, so that the open eye was still the one facing out. Simultaneous recordings of brain activity confirmed that the brain hemisphere corresponding to the open eye was always awake, while the hemisphere corresponding to the closed eye was the one in deep sleep.
The one-eyed tactic was effective: when an attacking predator was simulated on a video screen, the birds sleeping with one eye open were able to react in a fraction of a second – far faster than if they had been in deep sleep with both eyes shut.
Humans are not capable of unihemispheric sleep, although at least one writer has played with the fantasy. Damon Runyon wrote of how he once played cards with a fading champion card player who now lacked the stamina to stay awake during marathon games of gin rummy lasting eight or ten hours. When the man lost a game after making a bad play, the punters betting on him to win clamoured to remove their bets from the next game, on the grounds that he was asleep. Then someone pointed out that the allegedly sleeping player’s eyes were open, so he must be awake. ‘The one on your side is’, retorted one of the backers, ‘but the one on the other side is closed. He is sleeping one-eye.’
Nice, not naughty (#ulink_f454c206-f464-5b51-a885-99cef8a7c075)
Like all other forms of pleasure, sleep may become a passion.
Jean-Anthelme Brillat-Savarin, The Physiology of Taste (1825)
Sleep is far more than just a biological necessity. It is also a neglected source of pleasure. Consider this. Activities that are biologically important for survival and reproduction tend to be enjoyable: think of sex, or eating, or drinking, or being successful. Pleasure is one of nature’s ways of ensuring that animals do enough of the right things. Whatever happened to sleep? It is clearly essential for survival, and yet for many people it is merely a maintenance activity that brings little positive enjoyment. They sleep because they have to rather than because they want to.
In some respects, sleep has acquired the dismal status that eating had in post-war Britain, where austerity and a cultural blind spot reduced the culinary arts to a joyless act of refuelling. Bland, fatty food was daily shovelled in to keep the boilers stoked, with scant attention paid to its preparation or enjoyment. Fortunately, Britain has since developed more enlightened (if not self-indulgent) attitudes to food, and recent decades have witnessed cooking and eating emerge as pleasurable activities in their own right. For some people in wealthy nations, cooking and eating have become more a form of entertainment than a biological function.
Meanwhile, sleep is mired in the cultural equivalent of a 1950s British canteen meal: an inadequate and faintly unhealthy affair, indifferently concocted and consumed with more haste than enjoyment. Too many people regard sleep as the brain’s equivalent of fast food or overboiled cabbage. If gastronomy is ‘the reasoned comprehension of everything connected with the nourishment of man’, as it was originally defined, then should we not start thinking about sleep in the same way? I hope that by the end of this book you will be pondering the gourmet delights of sleeping, napping and dreaming, and starting to savour more of their lost pleasures for yourself.
PART II Insufficiencies (#ulink_330b3f66-5320-565b-852f-411cb70abccd)
2 Sleepy People (#ulink_e05442f8-5755-5aba-af92-a246577561ed)
She looked a little worn out, a little tired, but, then again, didn’t everybody? We all look a bit tired, these days, some more than others.
William Boyd, Armadillo (1998)
Many of us in our everyday lives are getting sleep of inadequate quantity and quality, and this is bad for our mental and physical health. Lack of sleep makes us inefficient at work, dangerous behind the wheel of a car and unattractive to be with; it lowers the quality of our lives, causes accidents and makes us more vulnerable to illness. And it is unpleasant.
I am not referring here to the acute sleep deprivation that comes from occasionally staying up all night, although that is common enough in professions such as medicine, the military and politics. Rather, I am talking about the chronic sleep deprivation that accumulates as we continually stint ourselves of sleep, day in and day out, because of the conflicting demands of work and leisure, or because of a sleep disorder, or just because we do not think sleep is important. So, what are the reasons for believing that sleep deprivation is a real problem?
Are we sleep-deprived? (#ulink_d2dc7e05-d856-5dd1-a091-37a92322eef6)
Eight hours they give to sleep.
Sir Thomas More, Utopia (1551)
The evidence that chronic sleep deprivation is a common feature of contemporary life comes in several interlinked strands. We will start with perhaps the most obvious one of all: the observation that many people feel sleepy when they are awake.
Assessing the extent of daytime tiredness in society is tricky, not least because so many people have come to regard feeling tired as normal. Nonetheless, numerous scientific studies have unearthed evidence that the problem is real and widespread. For example, a 2001 poll of Americans’ sleeping habits found that 22 per cent of adults felt so sleepy during the day that it interfered with their activities. A 1994 survey found that 5 per cent of the British population were experiencing severe daytime sleepiness, while a further 15 per cent felt moderately sleepy during the day. It also found that the people suffering from daytime sleepiness were twice as likely to have a vehicle accident.
A similar picture has emerged from other countries. For instance, a recent study discovered that 10 per cent of middle-aged Finns were excessively tired and tended to fall asleep unintentionally during the day. Their sleepiness was statistically associated with an array of nasty things, including a heightened risk of traffic accidents, premature retirement, depression and anxiety. In Sweden, 9 per cent of adults were found to be suffering from daytime sleepiness, while a survey in Warsaw recorded that 21 per cent of adults felt moderately sleepy during the day. Australian researchers detected excessive daytime sleepiness in 11 per cent of adults. You get the picture. Not even the youngest and healthiest are immune. A French investigation of 58,000 army conscripts discovered that 5 per cent of these fit young men were affected by excessive daytime sleepiness and 14 per cent of them were sufficiently tired to sleep during the day.
Overall, it is safe to conclude that at least one in ten adults in the general population (you, me and the people next door) are currently affected by moderate or severe daytime sleepiness. Some scientists believe the situation is much worse, with up to one in three adults suffering from significant sleepiness. A major review undertaken by the US National Commission on Sleep Disorders Research estimated that as many as 70 million Americans – more than a quarter of the population – were suffering from sleep deprivation or some form of sleep problem, at a direct cost to the national health care bill of about 16 billion dollars a year. The Commission’s report concluded that:
A convincing body of scientific evidence and witness testimony indicates that many Americans are severely sleep-deprived and, therefore, dangerously sleepy during the day … By any measuring stick, the deaths, illness, and damage due to sleep deprivation and sleep disorders represents a substantial problem for American society.
The problem appears to have deepened over time. Objective evidence about historical changes in sleepiness is hard to find, but there is some. A standard psychological test of personality, which has been regularly administered to large numbers of Americans since the 1930s, revealed that the proportion of men who felt tired during the day was significantly higher in the 1980s than it had been in the 1930s. And the average amount of sleep American students get has fallen by more than one hour over the past three decades. We seem to be a generally wearier bunch than our forebears.
Tired people are certainly common enough in the doctor’s waiting room. Physicians frequently encounter patients complaining of feeling tired all the time. The condition even has its own acronym, TATT. Of course not everyone who feels tired all the time is suffering from a lack of sleep. Chronic fatigue can result from anaemia, diabetes, cancer, depression and a whole host of other medical disorders. The distressing condition known as chronic fatigue syndrome (CFS), also referred to as myalgic encephalomyelitis (ME), is characterised by debilitating fatigue, pain in the muscles and joints, impairments in thinking and a general, horrible malaise. CFS is a distinct medical condition that cannot be attributed simply to lack of sleep. The origins of CFS remain controversial, but current theories focus on a combination of malfunctioning immune reactions and psychological factors.
CFS and other medical conditions undoubtedly account for some of the tiredness in society, but not much. The fact is that most people who feel tired during the day are just that – tired. They are tired because they have not been getting enough sleep. This explanation is so simple and so blindingly obvious that it is frequently overlooked.
Ordinary, everyday tiredness does not always require a medical explanation, but one is often sought nonetheless. ‘Exhaustion’ has become a voguish affliction of actors, pop stars and other celebrities. From time to time, a distraught and haggard celeb will flee to a clinic feeling, well, exhausted. The clinic duly subjects them to a battery of medical tests to establish whether they have diabetes, anaemia, ME or a thyroid disorder, while the media throb with stories about personal relationship problems, nervous breakdowns, exotic diets, exotic drugs, professional insecurities and emotional crises – just about everything, in fact, apart from plain tiredness. But given the long hours they are sometimes expected to work, plus the jet lag-inducing international travelling, it would be surprising if our stars of stage and screen did not occasionally feel very tired.
Another reason for believing that sleep deprivation is a common problem is that many of us get less sleep than we want or need, and considerably less than the proverbial eight hours we all supposedly aspire to. The evidence on this point is clear. For example, research found that in the 1990s young American adults were sleeping for an average of 7.3 hours a night. However, even this modest figure was inflated by weekend lie-ins: on weekday nights, Americans slept for an average of only 6.7 hours. A more recent study, which assessed the sleep patterns of middle-aged adults, found an average of only 6.2 hours. Similar conclusions have emerged from other countries. To give just a few illustrations, a survey in Poland found that adults there slept for 7.1 hours on workday nights, while Korean university students averaged 6.7 hours. When the Japanese Ministry of Health conducted a large survey they discovered that almost two thirds normally slept less than seven hours a night, and more than a quarter slept less than six hours. Worse still, half of Japanese high school students reported sleeping six hours or less on weekdays.
The research leaves little doubt that most adults in the USA, UK and other industrialised nations get substantially less than eight hours’ sleep most nights of the week, and many get less than seven. But does that matter? How much should we sleep?
The mythical inhabitants of Sir Thomas More’s idyllic island state of Utopia accorded sleep the priority it truly deserves. They slept for eight solid hours each night. Of the remaining 16 hours, work accounted for only six. (Sensible people.) The Utopians worked for three hours before noon then ate lunch; after lunch they rested for two hours, worked for another three hours then ate supper. They went to bed at about eight in the evening and slept for eight hours. The rest of each day they did as they pleased. Not quite the urban chic lifestyle, perhaps, but a refreshingly different perspective on life.
Conventional wisdom still holds that we need about eight hours of sleep a night. For most of us, however, the reality falls far short of the Utopian ideal, except perhaps at weekends and when we are on holiday. But is an average of, say, six or seven hours a night enough? Obviously, we cannot use Thomas More’s sixteenth-century fantasy as a scientific yardstick. So how do we judge the adequacy of sleep?
One approach is to ask people whether they think they are getting enough sleep. A recent study of more than twelve thousand adults did just that, and found that 20 per cent of them felt they were not getting sufficient sleep. Unsurprisingly, one of the factors most strongly associated with insufficient sleep was working long hours. Further evidence came from the Planet Project, said to be the largest opinion poll ever carried out. In 2000, an Internet-based survey was conducted with 1.26 million people in 251 countries. When asked how much sleep they needed in order to feel rested, 47 per cent of people replied eight hours or more. But when asked how much sleep they actually got, only 15 per cent reported sleeping eight hours or more, while 8 per cent said they got less than five hours a night. Many respondents reported having gone without sleep for long periods, whereas a mere 6 per cent said they had never missed a night’s sleep.
Six or seven hours of sleep a night is probably not enough for many people on a long-term basis. The experimental evidence suggests that the underlying sleep tendency for a typical healthy adult – that is, the amount of sleep they would take if completely liberated from work schedules and other constraints – is more like eight or eight and a half hours a night. This implies a shortfall of around an hour and a half each night. A shortfall of this size almost certainly matters. Restricting someone’s sleep by an hour and a half for just one night will measurably reduce their daytime alertness. The cumulative effects, when sleep is short-changed night after night, are far more pervasive. We shall be looking at the psychological and physical consequences of chronic sleep deprivation in the next two chapters.
A substantial nightly shortfall in sleep is difficult to sustain for more than five or six days in succession without sleepiness seriously impairing daytime alertness, mood and performance. This aspect of human biology might conceivably have contributed to the establishment of the seven-day week, comprising five or six days of work followed by one or two days of legitimised rest, as a standard unit of time. Most humans have been following the seven-day pattern for thousands of years. The seven-day week dates back to the pre-Biblical Sumerian and Babylonian civilisations. Right from the outset, one day of the week was deemed to be a day of rest and recreation. The Babylonians originally named their seven days after the five visible planets plus the Sun and the Moon, but the choice of seven otherwise has no objective basis in astronomy or any obvious feature of the physical environment. The Romans later adopted the seven-day week, dabbled with eight, then reverted to seven. The seven-day week appeared in the Bible, again with the inherent concept of a day of rest. According to the Biblical account of the Creation, God laboured for six days and rested on the seventh. Nowadays, people who work long hours and sleep for only six or seven hours a night really do need that extra time in bed at weekends to stave off sleep deprivation.
The thesis that many people are chronically sleep-deprived is not without its sceptics, however. Yvonne Harrison and Jim Horne at Loughborough University have argued that we all have the capacity to sleep more than we usually do, but only in the way that we can carry on eating after our physiological need for food has been satisfied. In support of their sceptical position, Harrison and Horne have cited, for example, an experiment in which healthy young adults slept for up to ten hours a night for two weeks, getting an extra hour or so of sleep each night. This additional sleep produced some improvements in their reaction times and a slight reduction in daytime sleepiness. However, there were no significant improvements in the volunteers’ subjective ratings of their own mood or sleepiness.
Scientists are paid to be sceptical, and counterblasts are an essential part of scientific debate. Nonetheless, such arguments must be set against all the other strands of evidence showing that chronic sleep deprivation is a real and widespread phenomenon. We have considered some of that evidence and there is more to come. First, though, what about you?
Are you sleep-deprived? (#ulink_5bc6e4af-67d9-577d-8861-8e93fe9ae0f7)
‘… Are you going to bed, Holmes?’
‘No: I am not tired. I have a curious constitution. I never remember feeling tired by work, though idleness exhausts me completely.’
Sir Arthur Conan Doyle, The Sign of Four (1890)
There is no universal, one-size-fits-all figure for the right amount of sleep. Individuals differ considerably in their sleep requirements. The conventional standard of eight hours a night is somewhat arbitrary, though not far off the mark for most people. But the best yardstick for you is your own preferred sleep duration. You can measure this by conducting a simple, if time-consuming, experiment on yourself. You will need two weeks of complete freedom from the tyranny of work schedules and alarm clocks, which means you will probably have to wait until your next long holiday (and possibly much longer if you have small children).
What you do is this. Every night for about two weeks, go to bed at approximately the same time. Make a note of the exact time just before you turn off the light to go to sleep. Then sleep to your heart’s content until you wake spontaneously the next morning – not with the aid of an alarm clock. Note down the time when you woke up and, ideally, a more precise time for when you think you fell asleep the night before. (All being well, this should have been within 10–20 minutes of turning out the light.) Your time of waking should be when you first became fully conscious, not when you eventually stumbled out of bed. Then calculate how long you spent sleeping. The experiment will work much better if you do not roll over after waking and doze for a further hour or two before getting up.
Ignore the figures for the first few days, because you will probably be sleeping longer to compensate for your prior sleep deficit. We tend to feel sleepy on relaxing holidays and at weekends because reality has finally caught up with us; when the usual pressures and stimulation that keep us going through the working week are suddenly removed, we sleep more to catch up on the backlog. This extra sleeping is only transitory, however. Once you have caught up and reached equilibrium you should start to feel livelier and more energetic during the day. Unfortunately, by that time the holiday has usually ended and the normal regime of late nights and early mornings resumes.
After a few days, your nightly sleep duration should settle down to a stable figure. Take the average over the final few days: this represents your preferred sleep duration. It should be somewhere between seven and nine hours, although not everyone fits this pattern. Unless you are elderly or have an unusually relaxed lifestyle, your preferred sleep duration will probably be longer than the time you normally spend sleeping. If the difference is very large – say, two or three hours a night – you could be storing up serious trouble for yourself.
Reasons for not sleeping (#ulink_b0ddfa16-24ea-5a90-9bba-8db66077f2c0)
Why all this sleep? – seven, eight, nine, ten hours perhaps – with a living to make, work to be done, thoughts to be thought, obligations to keep, a soul to save, friends to refrain from losing, pleasure to seek, and that prodigious host of activities known as life?
Walter de la Mare, Behold, This Dreamer. (1939)
Another reason for believing that sleep deprivation is widespread is that we sleep less nowadays than our ancestors did. There has been a major shift in sleep patterns in industrialised nations over the past century, the net result of which is less sleep.
William Dement of Stanford University has argued that humanity is in the midst of a ‘pandemic of fatigue’. Dement estimates that people in industrialised countries now sleep on average an hour and a half less each night than they would have done a century ago, and that most of us consequently walk around with an accumulated sleep deficit of 25–30 hours. If true, this means we would have to sleep for an extra two hours a night for two weeks to clear the backlog and return to equilibrium. Some of us come close to doing just that when we take a two-week holiday.
Lifestyles in industrialised societies have altered radically over the past century in ways that have consistently eroded the status of sleep and dreaming, leaving many of us now probably sleeping less than at any other period in human history. We live in an era when many people work long hours, where we have vastly more opportunities for entertainment and leisure, and where sleep is widely regarded as the poor relation to other pursuits. Humanity has inadvertently created lots of reasons for not sleeping.
One reason for not sleeping is that there is always so much work to do. Many sectors of society now work longer hours, on more days, than ever before. In early nineteenth-century Britain there were some 40 days in the year when the Bank of England shut its doors to observe saints’ days and anniversaries. By 1830 the number of such holidays had dropped to 18 days a year, and nowadays there are fewer than ten. Not only do we spend longer at work, we also spend longer getting to and from work, as commutes have grown both in distance and duration. Time spent stuck in a car or public transport is time that cannot be spent in bed. Ironically, the technological revolution has failed to free us from the shackles of paid work. Quite the reverse, in fact – it has given us the wherewithal to work more productively all day, every day. James Gleick made the point beautifully in Faster, his glorious exposé of our no-time-to-lose society:
Marketers and technologists anticipate your desires with fast ovens, quick playback, quick freezing, and fast credit. We bank the extra minutes that flow from these innovations, yet we feel impoverished and we cut back – on breakfast, on lunch, on sleep, on daydreams.
Cheap mobile communications enable us to stay in touch wherever we are, 24 hours a day. Copious amounts of caffeine, the world’s most popular psychoactive drug, help to keep us awake as we squeeze ever more into the day. The puritan work ethic and the cult of time management nag us to do a little bit more at the beginning and end of each day. So we get less sleep. But that is stupid, because people who cut back on their sleep achieve less and feel bad into the bargain. They end up stumbling through the day, fatigued and underperforming, without even realising what they are doing to themselves. They become, to quote one scientific paper, borderline retarded.
The idea of being able to get by on little or no sleep might appeal to some driven souls who would rather use the extra time for other things. (Some people seem to find being at work easier than living a real life.) In J. G. Ballard’s short story ‘Manhole 69’, a scientist who has entirely expunged the need to sleep from three human volunteers sneeringly declares that:
For the first time Man will be living a full twenty-four hour day, not spending a third of it as an invalid, snoring his way through an eight-hour peepshow of infantile erotica.
(Ballard’s sleepless volunteers, needless to say, meet a grisly fate.) If the fantasy of doing with less sleep ever became a reality – which, mercifully, it cannot – those extra hours of wakefulness would just be absorbed by more work. If we could all survive working 20 hours a day then the 20-hour day would become the norm. And we would still feel there were not enough hours in the day.
Fortunately, not everyone aspires to a sleepless world. A few highly successful businessmen have come out of the closet in recent years and openly admitted to sleeping for eight hours or more a night (although some cynics have pointed out that these captains of industry can only afford to have all that sleep because they are amply supported by minions working ridiculously long hours).
Britain is rapidly following the USA in becoming a fully-fledged 24/7 society where the consumer is king and nothing ever closes. Consumers really do want the freedom and flexibility to shop, bank or be entertained at any hour of the day or night, and governments are having to respond to their demands for public services to be continuously on tap, providing 24/7 facilities to the taxpayers who fund them. In 2001 the British government published a report called ‘Open All Hours’, explaining how public services were raising their game to meet the requirements of the 24-hour society. The report highlighted examples of how public services had responded to demands for extended opening hours. In his foreword, the Prime Minister wrote that ‘people living busy working lives … should be able to access services how and when they want’. The idea of modernising services to suit the needs and convenience of the public is surely laudable and uncontroversial. But there is something crucial missing from the cost-benefit analysis: the impact the 24-hour society is having on the ability of the people who are providing and consuming those services to get enough sleep.
Whatever happened to the technology-enabled revolution in leisure, which the future-watchers so confidently predicted in the 1960s? The main concern in those days was that we would all have too much free time on our hands, not too little. Sebastian de Grazia, one of the more thoughtful advocates from that era, argued for a return to the inner peace that can only come from a capacity for true idleness, combined with an escape from the constant stimulation that prevents people from ever being alone with themselves:
Perhaps you can judge the inner health of a land by the capacity of its people to do nothing – to lie abed musing, to amble about aimlessly, to sit having coffee – because whoever can do nothing, letting his thoughts go where they may, must be at peace with himself.
If the work ethic does not keep us from our beds, then our insatiable lust for entertainment and amusement surely will. As the Irish poet Thomas Moore put it, we are inclined to steal a few hours from the night:
’Tis never too late for delight, my dear;
And the best of all ways
To lengthen our days
Is to steal a few hours from the night, my dear!
In Shakespeare’s Twelfth Night the reprobates Sir Toby Belch and Sir Andrew Aguecheek have been up drinking all night. ‘I know to be up late is to be up late,’ contests Sir Andrew. ‘A false conclusion!’ avers Sir Toby: ‘To be up after midnight and to go to bed then, is early.’
The range of distractions and temptations to seduce us away from our beds has mushroomed since Shakespeare’s day. There is so much more to do in developed nations, and so much more wealth to do it with. The only quantity that has remained doggedly constant is the amount of time we have. There are still only 1,440 minutes in a day. So, we opt for the immediate fix of pleasure and stay up late. We know deep down that we will suffer the next day in mood, alertness and performance, but the lures are too appealing and their pleasures are instant.
Psychologists have a technical term – delayed gratification – to describe an individual’s ability to forgo an immediate reward in return for a bigger reward later on. It so happens that a capacity for delayed gratification is correlated with intelligence and attainment in life. Most of us, however, display a lamentable lack of delayed gratification when it comes to sleep. William Dement coined another term, ‘hedomasochism’, to describe the irrational belief that we can do it all, achieving ever more in our work, in our family lives and in our. leisure time, all at the expense of sleep. We cannot.
Ancient and modern (#ulink_f3cad88c-4ae4-5cd1-aa99-49261645811e)
We rise with the lark and go to bed with the lamb.
Nicholas Breton, The Court and Country (1618)
The current predilection for staying awake all hours is very recent in historical terms, let alone when measured against the span of biological evolution. It really took root following the invention of the electric filament light bulb by Thomas Edison in 1879, a negligible fraction of an instant ago in evolutionary terms. Of course, people did stay up after dark in the days before cheap electric lighting – just much less.
There have only ever been two ways for humans to deal with the night: to sleep and doze through it or to light it artificially. Until the nineteenth century the only practical source of artificial light was fire in one form or another. When humans depended on expensive candles or oil for artificial light they went to bed earlier and stayed there longer, unless they were in the wealthy minority. Few people did much work after dark. And when they did use artificial lighting, the fires and candles (and later, the gas mantles) generated light of insufficient intensity to reset their internal biological clocks in the way that much brighter electric lighting can. One electric light bulb produces as much light as a hundred candles and for only a tiny fraction of the cost. Unlike our ancestors, we no longer have to sleep, doze or stay in bed just because it is dark.
To appreciate how different life was for the majority of people living in temperate or northern climates, we need only wind the clock back to the eighteenth century. For most working folk, especially in winter, the sun provided the only serious illumination. The Natural History of Selborne, which was written by an English country clergyman called Gilbert White and published in 1788, describes life in a small village in rural England. White’s parochial history is said to be the fourth most published book in the English language. In one of his glimpses into the lives of Selborne’s human inhabitants, White reminds us that in the days before electric lighting, few people could afford the luxury of routinely staying awake for long during the hours of darkness. The villagers burned rushes to produce light, and even rushes cost money:
Working people burn no candle in the long days, because they rise and go to bed by daylight. Little farmers use rushes much in the short days, both morning and evening in the dairy and kitchen; but the very poor, who are always the worst economists, and therefore must continue very poor, buy an halfpenny candle every evening, which, in their blowing open rooms, does not burn much more than two hours. Thus have they only two hours’ light for their money instead of eleven.
In rural northern Europe of the Middle Ages it was pointless or impossible to work the fields during the dark days of winter, and too costly to heat and light the home all day. Whole families would therefore take to their beds for days at a time. You might not relish the prospect of spending days in bed with nothing to do. (Or perhaps you would?) Boredom would be the big enemy. Boredom, however, is a modern concept. Being alone with our thoughts and dreams is no longer enough for us.
Cold weather was another good reason for staying in bed, as Samuel Pepys recorded in this entry from his diary, written in December 1661:
All the morning at home, lying abed with my wife till 11 a-clock – such a habit we have got this winter, of lying long abed.
But even in warm, sunny climates, our ancestors probably spent more of their time in bed, especially in civilisations that practised the siesta.
In modern industrialised societies we are exposed to an artificial day that is extended by electric lighting and typically lasts for at least 16 hours, regardless of season. The marked seasonal fluctuations in the conception rate, which were once associated with the long winter nights, have almost disappeared now. Moreover, we now pack all of our sleep into a single block of time during the remaining seven or eight hours of darkness. This pattern of sleeping is biologically unusual: in most other species, sleep is split into two or more separate episodes in each 24-hour period. As we shall see, there are reasons for supposing that humans have not always slept in a single, compressed block.
Our daily cycle of sleep and wakefulness is largely determined for us by clocks rather than tiredness. Many of us go to bed when it is time to go to bed, not when we are tired, and wake when we have to wake, not when we choose to. Clocks with minute hands did not become available until the seventeenth century. Until quite recently in history, the majority of people relied on the sun for their timekeeping and lived in a world where the light intensity changed gradually at dawn and dusk, not instantaneously with the flick of a light switch. Moreover, they did not work in offices, factories or shops where they were required to be present at a certain time early every day.
How do humans sleep when left to their own devices in a world where it is dark for more than half the day – as would have been the case in pre-industrial northern countries during winter? To find out, Thomas Wehr at the National Institute of Mental Health in Maryland exposed volunteers to an experimental environment where it was dark for 14 hours a day and they could sleep freely. To begin with, the volunteers slept a lot (some more than 12 hours a day) as they caught up on their backlog. On average, they clocked up an additional 17 hours of sleep during the initial adjustment period. After their sleep deficits had been paid off, they settled down to an average sleep duration of eight and a quarter hours a day. Their mood and energy levels during the day improved consistently over the course of the experiment. When they were awake, they felt more awake and were more awake.
As well as sleeping longer, Wehr’s subjects also slept differently. Under these conditions of long, dark days and with nothing much to do, their sleep spontaneously divided into two distinct blocks. Typically, they would lie in a state of quiet rest each evening for about two hours before falling asleep. Then they would sleep for about four hours, usually waking at the end of an episode of dreaming. After another couple of hours of quiet rest they slept for a further four hours. On waking in the early morning they would lie in quiet rest for another couple of hours before rising.
Under these pseudoprimitive conditions, then, sleep was preceded, punctuated and terminated by long periods of quiet restfulness. This pattern of sleeping in two distinct blocks of time is known as biphasic sleep. It is typical of many mammals living in the wild and was probably the natural sleep pattern of our ancestors. We all retain the biological capacity for biphasic sleep, despite the profound changes in humanity’s environment since the advent of artificial lighting and the 24-hour society. A group of thoroughly modern Americans reverted to biphasic sleep within days of being given the opportunity. The nearest contemporary equivalent is the afternoon sleep of the siesta, a custom that still survives in some countries.
The predominant lifestyles of artificially-lit industrialised societies have led us to compress our sleep into a single block of seven or eight hours, as though we were living permanently in midsummer (but usually without the siesta). We have jettisoned the additional hours of quiet rest and the seasonal variations that once accompanied human sleep. We have also lost the main channel that once existed to our dreams. During the 14-hour nights, as they alternated between sleep and quiet rest, Wehr’s volunteers usually awoke from dreaming, giving them ample opportunity to lie quietly in the dark and contemplate their dreams. In later chapters we shall consider why dreaming evolved and what it does for us.
A quite different reason for believing that many people nowadays are chronically sleep-deprived is the mass of evidence that sleepiness is a major cause of accidental injuries and deaths. We shall now look at how sleepiness jeopardises safety-critical activities such as driving a car, flying an aeroplane, being a doctor, running a country and operating a nuclear power plant.
Sleepy drivers (#ulink_46e0c30e-4abe-5fe4-b6e1-a242f0727cef)
Till o’er their brows death-counterfeiting sleep
With leaden legs and batty wings doth creep.
William Shakespeare, A Midsummer Night’s Dream (1595–6)
Accidents are one of the leading causes of death in developed nations, and sleepy people are responsible for many of them. A remarkably large proportion of vehicle accidents are the direct or indirect result of tired drivers losing concentration or falling asleep at the wheel. A few examples may give a flavour of the carnage they cause. In March 1994 near Barstow in California, a pickup truck carrying 20 people veered off the road and crashed into a culvert after the driver apparently fell asleep at the wheel. The driver survived but 12 passengers died. In July 1995 near Roquemaure in France the driver of a bus carrying Spanish students from Amsterdam to Barcelona seemed to nod off then wake abruptly as his bus scraped a passing truck. He lost control and the bus swerved wildly before rolling over several times. The accident caused 22 deaths and 32 injuries. In February 2001 a sleep-deprived driver caused the Selby rail disaster in the UK, after he fell asleep at the wheel and his vehicle crashed onto a railway line. Ten train passengers died. The driver, Gary Hart, admitted getting no sleep the night before the crash, but claimed he could still drive safely. He was sent to prison.
Scientists have judged that sleepiness is a factor in at least 10 per cent of fatal car crashes in the USA and more than 50 per cent of fatal crashes in which a truck driver is killed. A 1994 report by the US National Commission on Sleep Disorders concluded that driver fatigue contributed to 54 per cent of all vehicle accidents in the USA. A comparable situation applies in the UK and elsewhere. Research concluded that at least 10 per cent of vehicle accidents in the UK are related to sleepiness, though some experts have put the figure much higher. Two large surveys in England found that sleepiness was a causal factor in 16 per cent of accidents to which the police were summoned and at least 20 per cent of accidents on motorways. Driving on a motorway is generally more monotonous than driving on a minor road, and monotony heightens the risk that a tired driver will fall asleep at the wheel. Half the drivers involved in these sleep-related accidents were men under the age of 30 and many of the accidents involved truck drivers, company cars or workers returning home from night shifts.
For every sleepy driver who actually crashes there are uncounted numbers who have had near misses. A large survey by the British Transport Research Laboratory found that 29 per cent of drivers had come close to falling asleep at the wheel within the previous year, while other research established that at least 5 per cent of middle-aged male drivers had actually fallen asleep while driving on several occasions. Not surprisingly, drivers suffering from moderate or severe daytime sleepiness are at least twice as likely to have a vehicle accident.
The official statistics tend to underestimate the true extent of the sleepiness problem, and it is easy to see why. Drivers who survive crashes are naturally reluctant to admit that they dozed off at the wheel, even if they recollect doing it. And it is difficult to prove legally that sleepiness caused a crash (especially if the driver is dead). Unlike alcohol, drugs or mechanical defects in a vehicle, sleepiness leaves few evidential traces. You can easily measure how drunk someone is at the roadside immediately after an accident. But measuring sleepiness is neither quick nor easy, and in practice it is simply not done.
The systematic under-reporting of fatigue was highlighted by accident statistics for Italian highways. Over the period from 1993 to 1997 the Italian authorities officially ascribed the cause as sleep in only 3 per cent of accidents. However, by analysing the data in more depth, researchers were able to estimate that sleepiness had probably contributed to about 22 per cent of accidents. If true, this means that the official statistics had underestimated the hazard of driver sleepiness by a factor of seven.
The time of day is a major element in the relationship between sleepiness and accidents. Thanks to our natural circadian rhythms, we all feel sleepier at certain times in the 24-hour cycle (usually in the early hours of the morning and again in the afternoon) regardless of how much sleep we have had. As expected, sleepiness-related vehicle accidents occur most often in the early hours of the morning and in the afternoon, during these natural peaks in sleepiness. Older drivers are particularly susceptible to afternoon sleepiness, whereas younger drivers are more prone to crashing late at night or in the early hours. When researchers analysed the data for accidents in which the driver had been injured or killed (excluding those involving alcohol) they found that young drivers were between five and ten times more likely to crash late at night than during the morning.
Driving late at night poses a risk for train drivers as well. In one study, scientists monitored train drivers while they drove the same route, both by day and at night. The train drivers felt much sleepier when driving at night, and physiological measurements mirrored their subjective feelings. Their brain waves, heart rates and eye movements at night were all characteristic of sleepy people. Four of the 11 drivers who were monitored admitted to dozing off during the night journey and two of them failed to respond to signals. Sleepiness has almost certainly caused numerous rail crashes over the years, but again the official statistics have systematically underestimated its importance.
The sleepiness experienced by many drivers is partly a product of natural cìrcadian variations in wakefulness. But much of the blame rests with simple lack of sleep. And when lack of sleep is combined with driving at odd hours, the effect can be lethal. Prevailing social attitudes towards this issue are frankly perverse. Many parents think nothing of packing their family into a car and then driving long distances to a holiday destination while they are seriously tired. They would be horrified at the thought of doing this while drunk, but the effects of tiredness and alcohol on their ability to drive safely are strikingly similar, as we shall see in the next chapter. The number of drivers involved is large. In August 1996 French researchers assessed the extent of sleep deprivation among drivers during the holiday season, by randomly stopping two thousand cars at tollbooths and interviewing the drivers. It transpired that half of them had slept less than they would normally have done during the previous 24 hours. On average, these happy holidaymaking drivers had slept for 3.4 hours less than normal.
Many long-haul truck drivers get insufficient sleep, with potentially serious consequences for their performance and safety. When investigators studied truck drivers working in the USA and Canada they found that the drivers spent on average slightly more than five hours a day in bed and got slightly less than five hours’ sleep. This was much less than their self-reported ideal of more than seven hours a day. Nearly half the truck drivers augmented their sleep by napping, but the naps were not sufficient to compensate. Video and EEG brainwave recordings revealed that more than half the drivers had at least one period of drowsiness while they were driving, and two actually fell asleep at the wheel.
Even changing the clocks can be dangerous. The switch to daylight-saving time each spring reduces the length of one night by one hour, which slightly disrupts sleep routines for the next few nights. The extra sleepiness caused by even this apparently trivial disturbance is enough to generate a statistically significant seasonal rise in traffic accidents. Fatal accidents peak on the day immediately following the changeover. Alcohol-related accidents also rise during the week after the clocks change, probably because the effects of alcohol and sleepiness reinforce each other.
You might think that changing clocks in the opposite direction each autumn would have the reverse effect, but you would be wrong. When researchers analysed 21 years of US vehicle accident statistics, they found that the switch back from daylight-saving time each autumn was also accompanied by an increase in fatal accidents – despite the fact that in this case everyone got an extra hour in bed. The likely explanation is that many people anticipated the extra hour in bed by staying up even later the night before. This was borne out by the fact that the rise in fatal accidents around the autumn changeover was most marked just before the clocks changed, and especially in the early hours of the morning.
One of the most alarming aspects of daytime sleepiness is that we can fall asleep briefly without even noticing. You are unlikely to be aware that you have slept unless your sleep has lasted for at least a couple of minutes. Tired people can therefore fall asleep at the wheel of a speeding vehicle for tens of seconds at a time and never even know. Researchers measured this phenomenon by waking volunteers after daytime naps of varying durations and asking them if they had been asleep. (Their sleep was confirmed by objective physiological measures.) After one minute of sleep only 15 per cent of subjects had any awareness that they had been asleep, and only 35 per cent were aware even after five minutes of sleep. The upshot is that so-called microsleeps, lasting anything up to a minute, often go unnoticed. Suppose a sleepy driver lapses into a microsleep for only ten seconds while driving on a motorway at 70 miles an hour. During that brief, unnoticed lapse in waking consciousness the vehicle will cover about 70 car lengths. It is virtually certain that while you are reading these words someone, somewhere is microsleeping at the wheel of a speeding vehicle.
One apparent obstacle to prosecuting drivers who fall asleep at the wheel is proving that they were aware of their dangerous state and are therefore legally responsible for their actions. No one could reasonably claim to have been completely unaware that they were dangerously drunk, but a driver might conceivably claim to have been oblivious of being sleepy before crashing. However, the experimental evidence suggests otherwise. Sleep does not occur spontaneously without prior warning in the form of sleepiness.
Drivers who fall asleep at the wheel may not recall the actual moment of falling asleep, but they will almost certainly remember feeling sleepy beforehand. Scientists established this by monitoring sleep-deprived volunteers while they drove a simulator. The sleepier the drivers felt, the more mistakes they made. Serious errors, of the type that might have caused a crash in real life, were always preceded by prolonged feelings of sleepiness. By the time an ‘accident’ took place the tired driver had invariably been consciously fighting sleepiness for some time. The strong implication is that drivers who fall asleep at the wheel in real life will almost certainly have felt noticeably sleepy beforehand. The problem is that so many sleepy drivers press on regardless, fighting their sleepiness and risking lives. Many drivers harbour the illusion that they will not fall asleep at the wheel provided they fight hard enough. What they fail to appreciate is that if you are sufficiently sleepy you will eventually fall asleep, no matter how hard you resist.
Not all sleepy drivers are sleepy because of sleep-deprived lifestyles. Some are sleepy because they have a medical sleep disorder, often undiagnosed. The most common of these, called sleep apnoea, involves the repeated interruption of breathing during sleep. We shall be taking a closer look at sleep apnoea in chapter 15. Individuals who suffer from this disorder can become severely sleep-deprived, although they rarely know why. The daytime sleepiness caused by the repeated disruption of their sleep every night can severely impair their driving performance.
Sleepy drivers not only have more accidents, they also have worse accidents. The hallmark of an accident caused by a driver falling asleep at the wheel is the absence of skidmarks. Of all the crashes that are attributed to drivers falling asleep, more than three quarters involve the car driving off the road and more than half involve high speeds.
Car and truck manufacturers have done little to tackle the safety hazard created by sleepy drivers. Driver fatigue remains one of the biggest weak spots in vehicle safety, perhaps because it is much easier to modify the design of a vehicle than to modify the behaviour of humans. However, some promising technology is being developed that may show the way. One system uses cameras mounted in the dashboard to track the driver’s eye movements. It exploits the fact that people blink in a characteristic way when they are about to fall asleep. The device warns the driver if the blink frequency indicates a risk of nodding off at the wheel. IBM is developing an even more sophisticated system, known as the Artificial Passenger. An intelligent computer, which knows the driver’s personal profile and interests, holds a conversation with the driver. It asks questions and even tells jokes (though humour is reportedly not yet one of its strengths). If the driver’s responses are slow, flat in intonation and fail to make sense, the Artificial Passenger may judge that the driver is sleepy and urgently needs to be revived. If so, it will automatically open one of the car’s windows, sound an alarm or even activate a device that sprays cold water in the dozing driver’s face.
Governments are only just beginning to wake up to the carnage caused on our roads by sleepiness, having focused for so long on the dangers of alcohol. And yet sleepiness accounts for far more road deaths than alcohol, let alone drugs.
Sleepy pilots (#ulink_dc39c136-f720-5caf-bff8-d732597e2a37)
My spirits grow dull, and fain I would beguile
The tedious day with sleep.
William Shakespeare, Hamlet (1601)
Fatigue and chronic sleep deprivation are obviously of crucial relevance to aviation safety. Tired pilots are bad pilots, for all the reasons that tired drivers are bad drivers. How big is the problem in practice?
Historically, severe fatigue among aircrews has sometimes been a major problem during crises where huge demands have been placed on precious personnel. Take, for example, the Berlin airlift of 1948–9. In June 1948 the forces of the former Soviet Union occupying eastern Germany began a blockade of road, rail and other communications between Berlin and the West. An international crisis ensued. The USA and UK mounted a huge airlift operation to supply West Berlin with food and other essential supplies. The airlift continued for 11 months until the Soviets eventually withdrew their blockade. During that time Allied planes delivered more than two million tons of food, fuel and other supplies to the beleaguered residents of West Berlin. To sustain this huge effort, the aircrews worked punishing schedules with grossly inadequate sleep. There were many accidents, some of them the result of fatigue. A special investigation during the crisis led to immediate improvements in the aircrews’ working conditions and sleeping quarters, which probably made a material contribution to the ultimate success of the whole operation.
Even in peacetime, tiredness is not unknown on the flight deck. Most airline flight crews experience some sleepiness and impairment in their performance, especially during long-haul and overnight flights. In one recent study, scientists from the British Defence Evaluation and Research Agency monitored 12 airline pilots during routine nine-hour flights between London and Miami. Recordings of their EEG brain-wave activity and eye movements revealed that 10 of the 12 pilots either slept or displayed signs of significant sleepiness during the flights. These episodes were often brief, lasting less than 20 seconds. Microsleeps of this brevity generally go unnoticed, and the pilots would probably have been unaware of drifting off.
Scientists from the NASA Ames Research Center in California also detected fatigue among flight crews on commercial long-haul flights. The crews on these flights, which crossed up to eight time zones, became measurably sleep-deprived. They felt more fatigued than normal, consumed more caffeine, ate more snacks and reported more minor health problems such as headaches, nasal congestion and back pain. Their sleep loss was made worse by the fact that their circadian rhythms did not have time to synchronise with local times. Their natural low points in alertness therefore often occurred while they were on duty, amplifying their sleepiness.
Jet lag is not just unpleasant and stressful – it also has physical effects on the brain. Researchers compared two groups of female flight attendants who had all been working on long-haul flights for at least five years. Half the women were in jobs that allowed them two weeks to recover between long-distance flights, while the other half usually had only a few days’ rest in between. The women who had little time between flights performed significantly worse on tests of learning and memory; their reactions were slower and they made more mistakes. More significantly, brain scans revealed distinct physical changes in their brains. A region of the brain known as the right temporal lobe had shrunk significantly. The women with the most shrunken right temporal lobes also had the highest levels of cortisol, a stress hormone that is known to affect the structure of the brain and the functioning of the immune system.
The implication of this research is that people who regularly fly long distances, crossing more than six or seven time zones, should ideally allow at least ten days to recover before doing it again. The research also raises questions about the policies of airlines that require their flight crews to fly long haul without adequate rest periods in between. The thought of sleepy, jet-lagged pilots with wizened right temporal lobes and impaired mental abilities slumped behind the controls of jumbo jets is mildly alarming.
Flying for a living can be tiring even when it does not involve crossing multiple time zones and becoming jet-lagged. Like workers in many other industries, flight crew are often required to start work early in the morning, and this alone can starve them of sleep. Researchers who monitored the sleep of female cabin crew found that when the women worked early mornings their sleep was reduced to an average of just over five hours. This is not enough sleep for the vast majority of people. Early-morning working was also unpleasant and mildly stressful for these women. They reported feeling apprehensive about having to rise early, they felt sleepy during the day and they complained more about their sleep being unrefreshing.
The only cure in situations like these is getting enough sleep, and at the right time of day. But that is not always possible on long-haul flights. Napping can provide a short-term palliative. If all else fails, a British firm has patented a technological aid to keep airline pilots awake. Worn like a wristwatch, it uses a motion sensor to monitor the pilot’s movements. A loud alarm sounds if there has been no movement for a few minutes. Personally, I would prefer not to find myself on a plane flown by a pilot who needs one of these devices. But if I do, I hope it works.
Space flight is even less conducive to sleep than air travel. Astronauts can and do sleep in space, but not very well. Space flight confuses the body’s internal clock and reduces both the quantity and quality of sleep. Astronauts on the Space Shuttle were typically getting only five or six hours of poor quality sleep a night, and often resorted to sleeping pills. More than 40 per cent of Space Shuttle astronauts took medication for sleep disturbances – about the same proportion as took drugs for motion sickness.
In recent years, NASA has been giving its astronauts doses of the ‘sleep hormone’ melatonin to help them sleep. (We shall see what melatonin does in chapter 6.) However, research by Charles Czeisler at Harvard Medical School found that melatonin actually had little beneficial effect on astronauts’ sleep. What did work, however, was covering the astronauts in electrodes to monitor their sleep. Czeisler discovered that Space Shuttle astronauts slept better when they were festooned with electrodes and physiological monitoring equipment. The most likely explanation is simple and psychological. The astronauts had probably been sleeping badly because they were so focused on performing their many duties. Swathing them in sleep-monitoring electrodes convinced them that sleep was also a legitimate and important part of their duties, and they consequently relaxed and slept better despite the marginal discomfort.
Sleepy doctors (#ulink_4696b113-aab3-5fcc-b50a-d8a6f9cdbc08)
Think not, is my eleventh commandment; and sleep when you can, is my twelfth.
Herman Melville, Moby-Dick (1851)
To find the prime example of skilled professionals who routinely perform demanding, safety-critical tasks while severely sleep-deprived we need look no further than medicine. Chronic sleep deprivation is rife among hospital doctors, who are not superhuman enough to be immune from its consequences. Lack of sleep impairs their mood, judgment, decision making, thinking abilities and communication skills just like anyone else. One commentator recently described medical training in the USA as ‘a gruelling endurance test in which patients are often those most at risk’. The situation in the UK is no better.
Just how tired are doctors? According to the research data, some of them are very tired indeed. A study of American physicians undergoing postgraduate medical training illustrates the problem. During a typical 36-hour period of on-call duty, the interns spent less than five hours in bed and slept for an average of less than four hours. That is not enough. Another American study found that three out of four residents in obstetrics and gynaecology were working between 61 and 100 hours a week, and more than two thirds reported getting less than three hours’ sleep while on night call. Perhaps unsurprisingly, a large majority wanted limits placed on their work hours, despite concerns that this might restrict their professional experience. Much the same is true for doctors in other countries. For instance, house officers in Stockholm hospitals were found to sleep for an average of only four hours when on night call.
Three or four hours’ sleep is not enough for most people. Research has shown that doctors who have slept for less than five hours in the previous 24 display significant deteriorations in their memory, intellectual skills, language and numeracy. Doctors working night shifts get less sleep than those on day duty, and their performance is consequently worse. A study at Stanford University found that emergency physicians slept for an average of 6.3 hours after working day shifts, but only 5.2 hours after night shifts. Their performance and mood suffered accordingly: those working nights had slower reaction times and took one third longer to perform a standard medical procedure. Their performance deteriorated during the course of a night shift and they became progressively more likely to make mistakes. They also felt less alert, less motivated, less happy and less clear-thinking than when they were on day shift. Given the choice, any sane patient would want to be treated by a doctor working day shifts.
As we shall see in the next chapter, sleep deprivation has a big impact on tasks requiring sustained concentration and effort. But tired people are often able to perform simple or engaging tasks in short bursts. Sleep-deprived doctors usually cope surprisingly well with brief but invigorating crises. Problems are more likely to arise with routine, repetitive tasks requiring prolonged attention. It might be relevant that the impact of sleep deprivation is found to vary somewhat between the different medical specialities, with surgeons being the least affected.
We will also see in the next chapter that sleep deprivation erodes our mood, motivation, social skills, communication skills, creativity and lateral thinking. Again, doctors are no exception. Psychologists who assessed junior doctors after a night of dealing with emergency admissions found deteriorations in their mood and motivation, as well as the usual impairment in short-term memory. Sleep-deprived doctors also perform significantly worse on measures of creative thinking and originality. They are less capable of solving complex problems that require originality and non-linear thinking, such as diagnosing an unusual condition.
To put icing on the cake, sleep-deprived doctors have an alarming tendency to fall asleep when driving their cars. An American study of paediatricians found that half of them admitted to having fallen asleep while driving, almost always after a night on duty. The on-call doctors notched up substantially more traffic accidents and traffic citations than their faculty colleagues. Their propensity to fall asleep at the wheel was unsurprising, considering they got less than three hours of sleep during on-call nights. So, after unintentionally jeopardising their patients’ lives while on duty in the hospital, sleep-deprived doctors put themselves and other road users at risk while driving home.
The madness of politicians (#ulink_70d805b8-dea4-5f00-9651-d4c1102fa389)
I have noted as something quite rare the sight of great persons who remain so utterly unmoved when engaged in high enterprises and in affairs of some moment that they do not even cut short their sleep.
Michel de Montaigne, ‘On Sleep’, Essays (1580)
Long hours and inadequate sleep are standard features of political life. Those highly motivated, hardy individuals who survive the fierce competition and reach the top must have an above-average capacity for coping with little sleep. Having got to the top, they then set a bad example to the rest of us by projecting an image of tireless and unceasing industry. To accuse a politician of looking tired is frankly insulting. But they are only human, and inside that aura of sleeplessness there often lurks a tired person who secretly wants to spend more time asleep in their own bed.
Mythology and image-making abound when politics meets sleep. During Margaret Thatcher’s tenure as prime minister an absurd myth was fostered that it is both feasible and admirable for people routinely to sleep for only four hours a night and work hard for the remaining twenty. Hogwash. With the possible exception of a tiny minority of extraordinary individuals, humans simply do not thrive or perform well for long on four hours’ sleep a night.
Negotiators sometimes deliberately exploit the debilitating effects of acute sleep deprivation to achieve their aims. People who have hardly slept for two or three days will agree to almost anything at four o’clock in the morning. Dragging out negotiations over several days may be irksome, but it can work if you make sure your side gets more sleep than the opposition. But more often than not, tiredness just gets in the way of rational politics. In 1997, after a sleep-deprived marathon of negotiation, representatives of 160 nations agreed the Kyoto Protocol, aimed at reducing global emissions of greenhouse gases. Three years later, fatigue helped to set back the environmental cause. In November 2000 an international summit convened in The Hague to thrash out unresolved problems left hanging by the Kyoto treaty. The negotiations ground on for 12 long days, leaving the delegates exhausted. In the early hours of the morning on the final day the British deputy prime minister, John Prescott, proposed a deal that he thought would break the logjam. But the deal collapsed, reportedly because the French delegate refused to make a difficult decision. A furious Prescott laid the blame squarely on the French environment minister. He told journalists: ‘She got cold feet, felt she could not explain it, said she was exhausted and tired and could not understand the detail and then refused to accept it. That is how the deal fell.’ The summit ended without reaching agreement.
The burden of work on the politicians and officials who run our nations has grown inexorably over the years. The number of decisions they must take has mushroomed, as the world has become an ever more complex, law-bound and media-scrutinised place. The insatiable demands of the 24-hour news media add greatly to the load. Political leaders are frequently overloaded, with insufficient time to think and formulate policy, let alone get enough sleep.
Academic observers of the British government scene calculated that between the 1960s and the 1990s the average working day for government ministers grew from 14 hours to 18 hours. The eminent political historian Peter Hennessy described the job of a British cabinet minister as ‘a conveyor belt to exhaustion and underachievement all round’, while a former senior adviser to the prime minister wrote that ‘Ministers are governed by diaries which seem designed to break them in physique or spirit in the shortest possible time.’
The diaries of the late Alan Clark, who served as a government minister in the 1980s and early 1990s, give illuminating glimpses into the sheer grind of ministerial life. Clark observed colleagues who were ‘boss-eyed’ with fatigue after working past midnight. One diary entry from 1984 describes how the civil servants would always find more work for him to do, no matter how little sleep he had had:
Today has been vilely full. Went early to Leicester after a late, late vote and impossible to drowse in the train as officials were watching me beadily in case (their excuse) anything in the brief ‘needed explaining’. I dropped off, as good as, several times during monologues at the various offices.
To add to the hazards of politics, Clark’s life was occasionally jeopardised by an exhausted government driver who had a tendency to nod off while conveying the minister along motorways at antisocial hours. Alan Clark’s experiences were by no means unusual. Geoffrey Howe, who was Foreign Secretary in the 1980s and who, like Alan Clark, worked under the notoriously unsleeping eye of Margaret Thatcher, described his gruelling work regime like this:
During six years at the Foreign Office I took home, to work through overnight while others slept, no less than 24 tonnes of paper … Six o’clock was my normal time for getting up. My average bedtime was about four hours earlier.
The long-hours culture affects not only the elected politicians but also the officials who serve them (and, some would claim, run the country). Sir John Coles, who was head of the British Diplomatic Service from 1994 to 1997, described the problem like this:
Long working hours, pressure and flurry were part of Foreign Office culture. We liked to feel busy and under pressure … But it became necessary to question some of this culture. These things did not necessarily lead to good policy. Tired, pressurised officials were liable to make mistakes.
The demands now are, if anything, even greater. In December 2000 Tony Blair was asked, during an Internet chat forum with members of the public, what he remembered dreaming about on the night after his first general election victory in 1997, and what was the last dream he remembered. The prime minister’s answer was revealing about the punishing lifestyle that goes with his job:
I don’t remember getting much sleep at all that night … After a couple of hours’ sleep, we were up early to prepare for going to Buckingham Palace. As for dreams, I’ve not had much chance for sleep over the past few days, let alone dreams.
Jet lag caused by frequent international travelling adds to the problem. In the immediate aftermath of the terrorist attacks in the USA on September 11, 2001, Tony Blair engaged in a gruelling programme of shuttle diplomacy that saw him travel more than 40,000 miles on 31 international flights in the space of a few weeks. And the fact that he then looked tired made the front pages of the newspapers.
British Members of Parliament work some of the strangest, if not the longest, hours of any legislature in the world. In October 2000 The Times published the results of one of the most detailed surveys ever carried out into MPs’ lifestyles. The survey revealed a nightmarish world of long hours and chronic sleep deprivation. Most MPs said they worked between 71 and 80 hours a week, with one in six working up to 90 hours a week. One government minister logged a working week of 91 hours in Westminster followed by 20 hours at the weekend, leaving an average of eight hours a day for everything else including travelling, family life and a little sleep.
The response from one MP was illustrative. The constituency he represented, and where his family still lived, was a long way from London. He would leave home at five a.m. on a Monday morning and return in the small hours of the following Friday morning. His weekend at home would be spent on constituency business, and then there were the occasional foreign trips with a parliamentary committee. He and his partner planned to go out together on Saturday nights but he was usually so tired by then he would fall asleep. Once, while driving home from London, he had almost fallen asleep at the wheel and crashed. There has been some modernisation of parliamentary schedules, in response to pressure from MPs, but the long-hours culture remains deeply embedded.
Some politicians cope with the long hours with the assistance of drugs of various kinds. In the USA, coke is a favourite – particularly the diet cola variety. During the US presidential election campaign in 2000, candidate Al Gore engaged in an electioneering programme of awesome intensity, involving 19-hour days and an itinerary that criss-crossed the continent. ‘Our campaign consists of a lot of long days and a lot of short nights,’ said Gore’s spokesman. ‘While some candidates may look for their feather pillows, Al Gore is looking for every single undecided voter he can find.’ To help him remain awake and vaguely sentient, Gore reportedly drank copious amounts of Diet Coke. One of his aides was explicit about the reason: ‘These are high-caffeine days. He needs his fuel to get through them.’ Sadly for Gore, the caffeine was not enough.
George W. Bush, who beat Al Gore by the slimmest of slim margins, became notorious during the election campaign for his verbal fluffs and tortured syntax. Whole books have been dedicated to Bush’s gaffes, malapropisms and garbled sentences. One American psychologist even suggested that Bush’s difficulties with the spoken word resulted from a lack of sleep in someone who apparently needed a lot of it.
Perhaps the defeated Al Gore could draw a minuscule crumb of comfort from an informal survey, which was conducted several months after the presidential election and reported to the International Conference for the Study of Dreams in July 2001. This survey found that conservative Republican supporters were nearly three times more likely to experience nightmares than their less conservative Democrat opponents. Half of the dreams recalled by Republicans were nightmares, compared with fewer than one in five of Democrats’ dreams. Moreover, the conservatives’ dreams were generally more frightening and more aggressive in content.
When the next big crisis erupts on the world stage, remember this. The politicians and officials who will be handling that crisis will be getting little sleep, perhaps for days at a time, and they will consequently become even more sleep-deprived than they already were. Their reactions, judgment, rationality, mood, memory, creativity and social skills will deteriorate, and they will become more prone to taking inappropriate risks. You might conclude that the world would be a safer and saner place if our leaders and their officials spent more time in bed (asleep).
Truly, madly, sleepily (#ulink_066d4b93-ca47-5819-88e3-8f715972c0e7)
I have an exposition of sleep come upon me.
William Shakespeare, A Midsummer Night’s Dream (1595–6)
The human errors caused by tiredness sometimes have truly catastrophic consequences, and there have been plenty of man-made disasters to prove it.
Tiredness lay behind the environmental disaster that occurred when the supertanker Exxon Valdez ran aground in Prince William Sound, Alaska, spilling 11 million gallons of crude oil into the pristine waters and polluting thousands of miles of shoreline. The official investigation by the US National Transportation Safety Board concluded that sleep deprivation was a direct cause. The accident took place just after midnight on 24 March 1989, when the Exxon Valdez was under the control of the third officer. He had slept for only six hours during the preceding 48 hours and was therefore substantially sleep-deprived. It appears that he fell asleep on duty. Media reporting at the time suggested that alcohol was to blame for the accident, but the real culprit was fatigue. In addition to the appalling environmental damage, one man’s tiredness cost his employer more than five billion dollars in punitive damages.
Tiredness contributed to the US Space Shuttle Challenger disaster. On a freezing cold morning in January 1986 the Challenger ascended for ten miles and then exploded, killing the crew of seven astronauts. It later emerged that crucial rubber O-ring seals had failed catastrophically at the low temperatures prevailing that morning. The US Presidential Commission that investigated the disaster concluded that there had been serious flaws in the decision-making processes leading up to the launch. The danger had been foreseeable, but tiredness had contributed to the bad decision to launch despite the icy conditions. Key managers had slept for less than two hours the night before and had been on duty since the early hours of the morning. They were at a dangerously low ebb when the fateful decision to launch was taken. The official report noted that ‘fatigue is not what caused the accident, but it didn’t help the decision-making process’. It also commented that ‘working excessive hours, while admirable, raises serious questions when it jeopardises job performance, particularly when critical management decisions are at stake’. Bear in mind that when official investigations search for the causes of disasters they instinctively focus on tangible, physical causes like rubber O-rings and air temperatures; intangible human factors like fatigue are seldom in the forefronts of investigators’ minds.
Lack of sleep has contributed to, if not caused, a string of disasters and near disasters in nuclear power plants. Many of them occurred in the early hours of the morning – a common feature of sleep-related accidents – and stemmed from failures by human operators to make sensible decisions when faced with the relevant information. Research has confirmed that nuclear power-plant operators who work night shifts experience real problems with sleepiness, distractibility and poor alertness. Even if they are not particularly sleep-deprived, they are unlikely to perform well in the early hours of the morning. And that is when the accidents happen.
The worst nuclear incident so far in the USA took place in March 1979, when the reactor at the Three Mile Island power station near Harrisburg in Pennsylvania came close to meltdown. The near-disaster at Three Mile Island arose in the early hours of the morning, after operators failed to recognise what their instruments were plainly telling them – namely, that an automatic valve had closed, cutting off the water supply to the coolant system. The reactor shut itself down automatically, as it was designed to do when a malfunction like that occurred. But a series of errors by the human operators led to a dangerous loss of coolant from the reactor core and almost turned an incident into a catastrophe. Radioactive gases were released from the partially exposed reactor core, but the containment vessel fortunately prevented them from escaping into the environment. Although no one died as a direct result of the Three Mile Island accident, it had a massive impact on the American nuclear industry. The damaged reactor took ten years to decontaminate and remained unusable. Fatigue is believed to have contributed to the operators’ repeated failures to handle the incident correctly.
The worst nuclear accident thus far in history occurred at the Chernobyl nuclear power station in April 1986. It too was sleep-related, and started in the early hours of the morning when the operators were at their lowest ebb. The disaster happened when the engineers operating one of the station’s four nuclear reactors made a series of irrational judgments. They attempted an ill-conceived experiment that involved shutting down the reactor’s regulatory and emergency safety systems and withdrawing most of the control rods from the core, while allowing the reactor to continue running. The operators exhibited the alarming propensity to take inappropriate risks that is characteristic of tired people. As a later report put it, they behaved ‘like intelligent idiots’.
The reckless behaviour of Chernobyl’s operators caused a chain reaction. At 1:23 a.m. on the morning of 26 April a series of explosions blew the reactor apart. There was a partial meltdown of the reactor’s graphite core and it caught fire. Large amounts of radioactive material were released into the environment – several times the amount created by the atom bombs dropped on Japan in World War Two. Some of it was carried by winds and contaminated several western European countries, including France and the UK. Thirty-two people at the Chernobyl plant died at the time of the accident and several more died soon after from severe radiation exposure. The long-term damage to the health of populations living in affected areas remains a matter of controversy, but it is undoubtedly huge. Several thousand people have died, or will die, as a result.
Over and over again, man-made disasters like Chernobyl and Exxon Valdez have occurred at night or in the early hours of the morning, when people’s reactions and judgment are at their weakest. We saw earlier that drivers are much more likely to have a serious crash late at night than in the middle of the morning. Almost everyone who works night shifts displays signs of sleepiness and impaired performance, and it is not difficult to see why. Working at night forces people to perform at a time when their biological clocks are telling them to sleep, and to sleep when their biological clocks are telling them they should be awake. They perform worse when they are at work, and they are less able to sleep when they go home, as a result of which they become tired and accident-prone. Add chronic sleep deprivation to the brew and you have a potentially lethal concoction. And we all have to live with the consequences.
The price of eternal vigilance is liberty (#ulink_2e1871fd-95d6-5a4a-840f-c5b271f36faa)
Care is heavy, therefore sleep you.
Thomas Dekker, Patient Grissil (1603)
If society were to recognise the true importance of sleep, then attitudes towards tiredness on the roads and in the workplace might become more enlightened. In a more sleep-conscious world it would no longer be socially acceptable, let alone admirable, for people to drive or turn up for work suffering from severe fatigue, any more than it is now acceptable to be drunk in the workplace or behind the wheel of a car. Napping during working hours would be tolerated and even encouraged, rather than stigmatised as a sign of sloth, drunkenness or illness. Meanwhile, society continues to turn a blind eye to people driving cars, flying aeroplanes, practising medicine, operating safety-critical machinery and running nations when they are mentally and physically impaired by lack of sleep.
In the next chapter we shall see that sleep-deprived people are bad at making decisions and communicating those decisions to others. Their judgment is impaired, they are easily distracted, they respond poorly to unexpected information, they lack flexibility, they persist with inappropriate solutions to problems and they are prone to taking foolish risks. These are not the characteristics any of us would wish to see in the people who make life-and-death decisions in the corridors of power, hospitals, flight decks or nuclear power stations.
3 Dead Tired (#ulink_d0cf0e7a-1da5-5fa3-893d-dcbfe8fec2a7)
You lack the season of all natures, sleep.
William Shakespeare, Macbeth (1606)
Does it really matter that many people in industrialised countries no longer get enough sleep of sufficient quality at the right times? We have seen one reason: the fact that sleepiness causes accidents. But far more than that, inadequate sleep matters because of what it does to our minds and our bodies each and every day.
Sleep is eloquent in its absence. We know that if we miss a night’s sleep we will feel bad the next day. But the unpleasant sensations of acute fatigue evaporate after a good night’s sleep and we soon forget. Far less obvious are the insidious, cumulative consequences of seldom getting quite enough sleep, night after night, week after week. Chronic sleep deprivation creeps up on us. It has pervasive effects on our mood, social skills and mental abilities – especially judgment, creative thinking and problem solving. It can also impair our physical health and make us more vulnerable to disease, as we shall see in the next chapter. However, the first and most obvious symptom of insufficient sleep is sleepiness, and that is where we shall start.
Sleepiness (#ulink_5308485c-ae0c-57db-bf98-8a1a2a23d417)
Life is one long process of getting tired.
Samuel Butler, Notebooks (1912)
The longer you go without sleep, the sleepier you feel. Objective measurements prove that there is indeed a close relationship between sleep deprivation and sleepiness. That relationship is ‘dose-dependent’, which means that the longer you have been deprived of sleep, the faster you will fall asleep when given the opportunity. Really tired people can fall asleep almost anywhere, as William Shakespeare observed:
Weariness
Can snore upon the flint, when resty sloth
Finds the down pillow hard.
If you are able to lie on a hard floor and go to sleep immediately during the middle of the day, you are probably sleep-deprived. (An obvious point, but no less true for that.)
Sleep will eventually force itself upon you if you go long enough without it. When scientists carry out sleep-deprivation experiments with human volunteers they often have to work quite hard to keep their subjects awake. Someone who has been deprived of sleep for two or three days requires stimulation, activity and variety to stop them falling asleep, no matter how well motivated they are to stay awake. Ian Oswald, a British scientist who conducted sleep-deprivation experiments in the 1960s, recalled walking the streets of Edinburgh flanked by exhausted volunteers whom he was working hard to keep awake. Even then, he would often see their eyelids closing as they walked along in a twilight state somewhere between waking and sleep.
Sleepiness and its flip side wakefulness determine how alive you feel and how well you perform every day of your life. But until the late 1970s there was no standard tool for measuring sleepiness. Then Mary Carskadon of Brown University in the USA invented a simple technique called the multiple sleep latency test (MSLT). It measures sleepiness like this. The subject is invited to go into a dark, quiet room in a sleep laboratory, to relax and fall asleep. Sensors detect the physiological signs of sleep (of which more later). As soon as the subject falls asleep, he or she is woken up. The key measurement is the time taken to fall asleep. The purpose of the MSLT is to measure daytime sleepiness, so the tests are generally carried out between ten in the morning and eight in the evening. The procedure is usually repeated four or five times during the course of a day.
The length of time between lying down and falling asleep is called the sleep latency. A daytime sleep latency of 15–25 minutes is generally interpreted as a reassuring sign of normality. Someone who is sleep-deprived will fall asleep faster. A sleep latency of less than ten minutes raises questions; there is a good chance that the person concerned will be experiencing intrusive daytime sleepiness, especially during the normal afternoon dip in wakefulness or when bored. A daytime sleep latency of less than five minutes usually signifies excessive tiredness, implying that the individual is substantially sleep-deprived or suffering from a sleep disorder.
Not everyone who falls asleep quickly in the MSLT is sleep-deprived, however. There are a few healthy people who can fall asleep in a trice, given the opportunity and the will. These individuals have the ability to go out like a light even after they have had unlimited amounts of sleep and without displaying any other signs of sleep deprivation. They just seem to be unusually good at relaxing and going to sleep during the day, regardless of their need for sleep. An unusually short sleep latency should therefore be viewed as strong evidence of sleep deprivation, but not conclusive proof.
The MSLT is conducted in a sleep laboratory, using electronic sensors to determine the onset of sleep objectively. There is, however, a crude, do-it-yourself version of the MSLT. This entails lying on a bed under sleep-friendly conditions – lights off, shoes off, TV off, no noises off, and so on – with one hand dangling over the edge of the bed and holding a metal object such as a spoon. Under the dangling hand rests a plate or some other hard surface. When you fall asleep your muscles relax and the spoon drops onto the plate with a loud clatter. All being well, you should then wake up, check your stopwatch and write down your sleep latency. If, on the other hand, you wake up several hours later to find your spoon lying on the plate, it may be that you are sleep-deprived. An even simpler way of assessing your own subjective sense of sleepiness is with a self-rating method called the Stanford Sleepiness Scale. This is a seven-point scale, ranging from 1 (defined as feeling active, vital, alert, wide awake), through 2 (functioning at a high level, not at peak), 3 (relaxed, not full alertness, responsive), 4 (a little foggy, not at peak, let down), 5 (tired, losing interest, slowed down), and 6 (drowsy, prefer to be lying down), to 7 (almost in a reverie, hard to stay awake).
Sleepiness is affected by many other factors besides the length of time since you last slept. Foremost among these is the time of day. Other things being equal, it is easier to fall asleep at certain times of the day and harder at other times. Wakefulness fluctuates naturally over the 24-hour cycle, with low points occurring in the early hours of the morning and again in the afternoon. This daily rhythm in wakefulness is mirrored by fluctuations in performance, which manifest themselves in many ways. For instance, you are more likely to crash your car or make a mistake when performing a difficult task in the early hours of the morning or in the afternoon. Sleep deprivation amplifies the effects of time of day, so the more sleep-deprived someone becomes, the deeper their daily troughs in wakefulness.
Stimulation and activity can mask sleepiness, at least for a while. Busy people often fail to notice how tired they really are until they relax at the weekend or on holiday. Their true state then becomes apparent. Sleepiness is even influenced to some extent by the nature of your previous activity. Experiments have confirmed, for example, that people feel sleepier and fall asleep more quickly after watching television than after taking a walk.
Fighting the beast (#ulink_5606a271-0a1e-5188-9fbc-1b32ee472e7b)
Thou art inclined to sleep; ’tis a good dullness,
And give it way: I know thou canst not choose.
William Shakespeare, The Tempest (1611)
What does it feel like to be seriously tired? For most of us real exhaustion is thankfully a rare experience. But for some, it is all too real. One of the most graphic accounts ever written about crushing fatigue can be found in the autobiography of the American aviator Charles Lindbergh. In 1927 Lindbergh made the first solo non-stop flight across the Atlantic in his single-engine plane The Spirit of St Louis. It lasted 33.5 hours. In his 1953 Pulitzer Prize-winning autobiography, Lindbergh described how his flight from New York to Paris came close to disaster – not because of mechanical failure or bad weather, but because of simple lack of sleep.
Before his marathon flight Lindbergh was told that it would be impossible for one man to fly an aeroplane alone for 30 or 40 hours without sleep. Lindbergh disagreed: he had worked for more than 40 hours at a time without sleep, so he did not see why he should be incapable of flying for that long sitting down. He was almost proved wrong.
The timing of Lindbergh’s departure remained uncertain until the last moment. It all depended on the weather. When an opportunity suddenly arose to take off the following morning at daybreak, Lindbergh went back to his hotel to cram in a few hours’ sleep. As a professional pilot he had learned from experience that every little bit of sleep helps. Even so, it was close to midnight before he reached his room, leaving barely three hours if he was to be ready to fly at dawn. As he eventually lay down to sleep, Lindbergh regretted the flawed planning that would force him to set off in a state of sleep deprivation. He knew he would have been better off starting his marathon fully rested – not just because that would make him a better pilot, but also because tiredness would prevent him from fully appreciating the experience. Lindbergh wanted to enjoy his flight. Even then, in those precious few hours, his sleep was further eroded when someone woke him to ask a stupid question. By three o’clock that morning Lindbergh was at the airfield preparing to take off. And so began his epic, sleepless flight across the Atlantic.
After only a few hours in the air, Lindbergh felt tiredness creeping up on him. How pleasant it would be, he mused, to doze off for a few seconds. He shook himself. He could not afford to feel like that so early in the trip. Later that day, and still less than nine hours into the flight, fatigue hit him again:
My eyes feel dry and hard as stones. The lids pull down with pounds of weight against their muscles. Keeping them open is like holding arms outstretched without support. After a minute or two of effort, I have to let them close … My mind clicks on and off, as though attached to an electric switch with which some outside force is tampering. I try letting one eyelid close at a time while I prop the other open with my will. But the effort’s too much. Sleep is winning. My whole body argues dully that nothing, nothing life can attain, is quite so desirable as sleep.
If sleepiness weighed so heavily upon him now, how could he get through the night, to say nothing of the dawn and another day and its night and possibly even the dawn after that? Lindbergh was ashamed. How could he let something as trifling as sleep ruin the record-breaking flight he had spent so many months planning? How could he face his sponsors and admit he had failed to reach Paris because he was sleepy? This must be how an exhausted sentry feels, he thought: unable to stay awake, yet knowing he will be shot if he is caught napping. He had no choice but to battle against his fatigue, minute by minute. In the end, it would all come down to sheer will power.
As the first traces of dawn began to appear on the second morning, Lindbergh felt the overwhelming desire to sleep falling over him like a quilt. Dawn was the time he had dreaded most:
Like salt in wounds, the light of day brings back my pains. Every cell of my being is on strike, sulking in protest, claiming that nothing, nothing in the world, could be worth such an effort; that man’s tissue was never made for such abuse. My back is stiff; my shoulders ache; my face burns; my eyes smart. It seems impossible to go on longer. All I want in life is to throw myself down flat, stretch out – and sleep.
Lindbergh searched for some way to stay alert. Shaking his body and stamping his feet no longer did any good. He had no coffee with him, but consoled himself with the thought that he had long since passed the stage when coffee could have helped. He pushed the stick forward and dived down into a ridge of cloud, pulling up sharply again after clipping through its summit. That woke him up a little, but not for long. He was thankful that The Spirit of St Louis had not been designed to be a stable aeroplane. The very instability that made it difficult to fly now guarded him against catastrophic errors. The slightest relaxation of pressure on stick or rudder would start a climbing or a diving turn, hauling him back from the borderland of sleep.
In the twentieth hour sleepiness temporarily gained the upper hand. Lindbergh suddenly awoke to find the plane diving and turning: he had been asleep with his eyes open. The realisation that he had lost control of himself and the plane was like an electric shock, and within seconds he was back in command. But as time passed, and no new emergencies occurred, he lapsed back into a dreamlike state, unsure whether he was dreaming through life or living through a dream. Over and over again he fell asleep with his eyes open, knowing he was falling asleep and unable to prevent it. Extreme measures were needed. He struck his face sharply with his hand, but felt hardly any sensation. He hit his face again, this time with all his strength. All he felt was numbness. Not even pain would come to his rescue. He broke open a capsule of ammonia and inhaled, but smelt nothing. Lindbergh realised how deadened his senses had become.
After 24 hours in the air and with more than a thousand miles still to go, Lindbergh seriously doubted whether he could stay awake long enough to avoid crashing into the Atlantic. But just as he felt death and failure staring him in the face, he began to turn the corner. The seriousness of his crisis had at last broken the spell of sleep and summoned up his last reserves of mental strength. He felt as though he was recuperating from a severe illness. And, as the history books relate, Charles A. Lindbergh made it to Paris and became an international hero. His remarkable last-minute rally was almost certainly a reflection of his circadian rhythm. His next peak of alertness came just in time. If his flight had continued much longer, he would inevitably have plunged back down into another circadian trough of fatigue from which he might never have ascended.
Lack of sleep has always been one of the least glamorous aspects of life at sea. In 1938 the 18-year-old Eric Newby signed on as an apprentice aboard one of the last square-rigger sailing ships. Newby’s autobiographical account of his voyage, The Last Grain Race, charts his experiences as he made the round trip from Belfast to Australia and back again via Cape Horn. The ship had a minimal crew, so each man worked hard and slept little. ‘I had never been so tired in my whole life,’ wrote Newby, ‘far too exhausted to appreciate the beautiful pyramids of sail towering above me.’ After coming off watch he would fall into a dreamless sleep, so deep that when he awoke and went up on deck again he felt like a sleepwalker. On the return voyage his ship was hit by an awe-inspiring storm that soon had the crew’s compartment awash in six inches of water. But the sailors who were not on duty snored through it all, so great was their appetite for sleep. Like soldiers preparing for the next battle, they lay ‘absorbing sleep greedily like medicine’.
The writer C. S. Forester charted the sleepiness of the long-distance mariner in his Hornblower novels, which relate the fictional Royal Navy career and Napoleonic War adventures of Horatio Hornblower, a character partly modelled on Admiral Horatio Nelson. In one story, the gallant Hornblower is exhausted from lack of sleep after a daring escape from France and a prolonged battle with pursuing enemy ships. Like Charles Lindbergh, Hornblower experiences the disturbing sensation that his mind has become disconnected from his body:
His voice sounded strange and distant in his own ears, like that of a stranger speaking from another room, as he issued his orders; the very hands with which he held the ropes seemed not to belong to him. It was as if there was a cleavage between the brain with which he was trying to think and the body which condescended to obey him.
Sleep deprivation was a fact of life for Hornblower’s real-life counterpart as well. When Horatio Nelson was commanding a Royal Navy warship he seldom had more than two hours of uninterrupted sleep and sometimes stayed on deck all night. However, like many leaders famed for coping with little sleep, Nelson had a well-developed ability to take catnaps during the day. He would nap in his cabin in a black leather armchair, his feet up on a chair. As we shall see later, a faculty for napping has enabled many high achievers to cope with meagre rations of night-time sleep.
Even in the twenty-first century, napping is a crucial skill for sailors – especially when sailing single-handed. In February 2001 the British yachtswoman Ellen MacArthur crossed the finishing line of the Vendée Globe boat race after 94 days alone at sea. She had travelled 24,000 miles across three oceans to become the fastest woman to sail single-handedly around the globe. For 13 weeks she had managed her 18-metre yacht in some of the world’s roughest seas by herself. The only way Ellen MacArthur could survive was to become a past master of napping, and divide her sleep into multiple brief naps. During the 94-day voyage she took 891 naps, each lasting on average 36 minutes, giving her a total of about five and a half hours of sleep a day. Even sleeping in such short bursts, MacArthur frequently had to rely on what she called her ‘sixth sense’ to wake her when something urgently required her attention.
A soil for peevishness (#ulink_31da901f-b36f-5d30-93c2-10b97a1ef0e7)
He that sleeps feels not the toothache.
William Shakespeare, Cymbeline (1609–10)
Lack of sleep does far more than just make us feel sleepy, however: its tentacles reach out and twist our emotional, cognitive and physical states. One of the first casualties is mood. Tired people are emotionally less resilient and more prone to irritation or sadness. Tiredness also impairs our social and emotional skills, with potentially damaging consequences for personal relationships. A tired person can be physically present but psychologically and emotionally absent. In The Screw-tape Letters, C. S. Lewis imagines an experienced devil instructing his neophyte nephew on how to corrupt a young human. The best way, he advises, is through fatigue:
The paradoxical thing is that moderate fatigue is a better soil for peevishness than absolute exhaustion … It is not fatigue simply as such that produces the anger, but unexpected demands on a man already tired.
After a night without sleep, healthy people exhibit clear disturbances in mood, which are characterised by irritability, tension and reduced vigour. These symptoms normally evaporate after a good night’s slumber. Sleep-deprived people, like drunks, lose their social inhibitions and behave in inappropriate ways; they are prone to outbursts of childish humour, which others around them do not always find hilarious. (And strangely, for reasons that remain unclear, acute sleep deprivation can also have the counterintuitive effect of stimulating the libido.)
Severe sleep deprivation can induce feelings of persecution and mild paranoia. It is well known among sleep scientists that the volunteers who take part in their sleep-deprivation experiments often become irritable and impatient. Some subjects become slightly paranoid, convinced that the researchers and fellow volunteers are plotting against them. In rare instances, exhaustion can provoke more dramatic changes. In one documented case, a previously healthy man became psychotic after four nights of badly disrupted sleep and believed he was the Messiah.
Chronic sleep deprivation – that state of never getting quite enough sleep, day in day out, over a prolonged period – is far more common in everyday life than the acute deprivation that comes from having no sleep at all for one or two nights. And chronic sleep deprivation can have just as much cumulative impact, leaving even the saintliest person with a shorter fuse. The writer John Seabrook described the debilitating fatigue that goes with having a small baby like this:
The burning eyes; the band of fatigue that tightens around the skull, a sensation some liken to the feeling that you’re always wearing a hat; the irritation – at each other, at friends, at the cat’s water bowl, which I kept kicking by accident …
Lack of sleep and tiredness are obviously not wholly responsible for the tetchiness, aggression and petty violence of everyday life, but it is a racing certainty that they contribute towards making the world a nastier place. Conversely, there is little doubt that good sleep makes us feel better. In one study, researchers issued volunteers with pocket computers on which they logged their sleep patterns, moods and social interactions over a two-week period. The results showed that going to sleep earlier in the evening was consistently associated with better mood and better social interactions the following day.
Tired people are stupid and reckless (#ulink_bbd9505f-01f8-5e16-b9e2-966c10e0ea01)
Fatigue makes women talk more and men talk less.
C. S. Lewis, The Screwtape Letters (1942)
Besides making us grumpy and poor company, sleep deprivation impairs our mental abilities in many subtle and not-so-subtle ways. In brief, tired people are stupid and reckless. Sleep deprivation damages our ability to perform tasks that require attention, thought, judgment, memory, social skills or communication skills – which covers the ground fairly comprehensively. Tired people also seem to lose sight of the consequences of their actions, liberating them to do silly and sometimes catastrophic things: the Chernobyl and Exxon Valdez disasters were just two examples.
Even modest sleep loss will measurably reduce your mental performance. After one night without sleep, you will have slower reactions, make more mistakes and find it harder to maintain attention. Unsurprisingly, two or three days of sleep deprivation produce even bigger impairments. Young adults are no more resistant than older people. If anything, they are more vulnerable. When researchers compared the consequences of one night of total sleep deprivation on healthy 80-year-olds and 20-year-olds, they recorded larger disturbances in the mood and cognitive performance of the younger subjects.
Reducing someone’s sleep for several nights in a row can undermine their performance just as much as completely depriving them of sleep for one or two nights. When scientists limited healthy young adults to an average of only five hours’ sleep a night for a week, the subjects became progressively sleepier and their performance deteriorated significantly. Two full nights of catch-up sleep (equivalent to a restful weekend) were needed to reverse the decline.
The armed forces have understandably maintained a long-standing interest in how well people hold up when they are deprived of sleep, as often happens in conflict. Experience shows that soldiers can continue to perform reasonably well after days of sleep deprivation under combat conditions, buoyed up by adrenaline, physical exertion and strong motivation. With sufficient stimulation and will power, military personnel can usually keep going without sleep for three or four days before they keel over. In one study, for example, men were assessed throughout a strenuous combat training course lasting several days. Some of the trainees were allowed no sleep at all, while others were permitted a few hours in the middle of the course. All the men displayed a substantial deterioration on measures of mood, vigilance and reaction time, with those who got no sleep performing even worse than those who got some. By the end, the trainees who had not slept at all were suffering from clinical symptoms including sensory disturbances.
Sleep-deprived people can often perform certain tasks reasonably well in short bursts, despite their fatigue. The real problems arise if they have to sustain their effort for any length of time. This lack of staying power was highlighted by experiments conducted in the 1950s at the Walter Reed Army Institute of Research in the USA. Sleep-deprived volunteers scored well in tests of reaction times when they were only required to react a few times over a period of one minute. But when they had to make lots of rapid responses spread irregularly over a period of 15 minutes, their performance fell apart. Sometimes they reacted quickly and sometimes they reacted very slowly or not at all. The more sleep-deprived they were, the more their responses varied. That experiment illustrates a general pattern that has emerged from studies of sleep deprivation – namely, that the performance of tired people becomes much more variable and inconsistent. Their accuracy and speed can fluctuate wildly over periods of a few minutes. In one study, for example, scientists monitored the performance of volunteers throughout an 88-hour period of total sleep deprivation. The subjects’ performance on a task requiring vigilance and coordination was much more variable (as well as just plain worse) than a comparison group, and the longer they went without sleep the more variable their performance became. These wild fluctuations in performance probably arose because their attention was repeatedly blotted out by microsleeps. As we saw earlier, someone who is very tired can lurch from wakefulness to sleep and back again in a matter of seconds without even noticing.
Much of the research on sleep deprivation has focused on how it impairs people’s ability to perform tasks requiring rapid but relatively simple decisions, involving very basic skills such as the ability to maintain attention under monotonous conditions. These skills are sensitive to sleep deprivation (which is partly why they have been so frequently measured) but they also have only a tenuous bearing on what happens in reality. The sorts of judgments and decisions we all have to make in real life usually demand far more than just the ability to stay awake and press buttons. Real decisions require us to assimilate and process complex, incomplete and often contradictory information, to keep track of our actions, assign priorities, ignore distractions and communicate with other people. The truly frightening aspect of sleep deprivation is the way it erodes all of these capacities.
Sleep-deprived people are bad at making complex decisions that require them to revise their plans in the light of unexpected news, to ignore irrelevant information and to communicate effectively. These are precisely the capabilities that we all need most when dealing with the vagaries of normal life – as do politicians, managers, doctors, military commanders and other key decision makers.
Even a single night without sleep will impair your ability to think flexibly and creatively. Sleep-deprived people perform badly on all aspects of creative thinking, including originality, flexibility, generating unusual ideas, being able to change strategy, word fluency and nonverbal planning. Tired people tend to persist with their current activity regardless of whether it is appropriate – a characteristic that psychologists call perseveration. In one cleverly revealing experiment, sleep-deprived volunteers played a realistic marketing game that required them to make complex decisions and then continually update those decisions in the light of new information. After 36 hours without sleep, the well-motivated subjects were still able to read and absorb written information. But their ability to make sound decisions based on that information deteriorated markedly. As they became more sleep-deprived they found it increasingly difficult to recognise when to change tactics in light of changed circumstances. Their thinking became rigid and they tended to persist with incorrect responses. Eventually, after 36 hours without sleep (the equivalent of losing just one night’s sleep) their ability to play the game collapsed.
Sleep-deprived people reveal their blunted creativity and mental inflexibility through alterations in their spoken language. After 36 hours of sustained wakefulness, people display a marked deterioration in verbal fluency and inventiveness. They are more reliant on routine responses and tend to become fixated with a particular category of words. They also start using inappropriate, monotonous or flattened intonation when reading out loud. Think about how people talk when they are drunk and you will get the picture. Tired people are bad at finding the right words. Their language becomes less spontaneous and expressive, and they are less willing to volunteer information that others might need to know. All in all, they are worse at communicating their thoughts, feelings, decisions and actions. Being a poor communicator is unhelpful, whether you are a head of state trying to deal with a crisis or simply someone who values their social life.
The supposedly robust adolescent is, if anything, even more vulnerable than older people. One study found that when youths aged 10–14 years were restricted to only five hours in bed for one night, their verbal creativity, verbal fluency and ability to learn new abstract concepts were all impaired. Less complex mental functions, such as rote learning, were unaffected by this modest degree of sleep restriction. So the sleep-deprived adolescent would still be able to go through the basic motions at school the next day, but would be unable to perform to anything like their true potential. And it is not entirely unknown for adolescents to go to school after getting less than a full night’s sleep.
As well as sapping our ability to perform, sleep deprivation also impairs our motivation. Tired people just can’t be bothered. In one experiment, researchers persuaded a group of male students to work continuously for 20 hours without sleep and then observed them in various social settings. Sleep deprivation diminished everyone’s performance, but the students who were working in groups performed even worse than those who were working individually. This was because working in a group gave them the opportunity to loaf – and they did.
Another alarming characteristic of sleep-deprived people, and something else they have in common with drunks, is their propensity to take risks. Experiments have shown that as people become more fatigued, they are more attracted by actions that might bring big rewards and less worried by the possible negative consequences of those actions. For instance, French scientists assessed the risk-taking propensities of military pilots who were involved in a maritime counter-terrorism exercise. This required them to make strenuous night flights, depriving them of sleep. The data showed that as the exercise progressed, the pilots became more impulsive. In effect, sleep-deprived people become more reckless and foolhardy. This is yet another characteristic that you would not wish to encounter in someone who is in charge of a hospital ward or a political crisis or a nuclear power station, or the family car for that matter.
Alcohol, beauty and old age (#ulink_8d776144-d30e-54b5-947b-b8ff5d5a1bc6)
It provokes the desire, but it takes away the performance.
William Shakespeare, Macbeth (1606)
Tired people resemble drunk people in several respects. Most obviously, tiredness and alcohol both hamper our ability to perform tasks that require judgment, attention, quick reactions and coordination – such as driving a car, for example. Missing a night’s sleep has an impact on driving skills comparable to drinking a substantial amount of alcohol. In both cases safe driving is no longer possible; in one case, however, it is both legal and socially acceptable.
To compare the effects of sleep deprivation and alcohol, researchers persuaded healthy young men to drive a simulator while under the influence of varying degrees of sleepiness and with varying blood-alcohol levels of up to 0.08 per cent. (For comparison, the legal limit for driving in most countries is 0.08 per cent blood alcohol and in Scandinavian countries it is 0.05 per cent.) Alcohol undermined their ability to maintain a suitable speed and road position, and so did sleep deprivation. Drivers who had been awake for 21 hours (hardly a remarkable feat) performed as badly as drivers with a blood-alcohol level of 0.08 per cent. So, next time you miss a night’s sleep, try to remember (if you can) that your driving ability will be as bad as if you had a blood-alcohol level that would be illegal in most countries.
Recent research has underlined the parallel between tiredness and alcohol. Scientists assessed volunteers driving on a closed course, both after drinking alcohol and after sleep deprivation. Detailed comparisons showed that both acute sleep deprivation (one night with no sleep) and chronic sleep deprivation (two hours less sleep than normal each night for a week) caused impairments in performance and reactions that were almost indistinguishable from those caused by illegally high blood-alcohol levels. The inescapable conclusion is that even relatively modest sleep deprivation, of the sort that many people experience in everyday life, has potentially dangerous consequences. Shaving a couple of hours off your sleep each night for a week can make you as incapable behind the wheel as a drunk driver.
Another striking similarity between sleep deprivation and alcohol is that as well as impairing our performance, sleep deprivation also undermines our ability to realise that our performance has been impaired, as we shall shortly see. (Try saying that sentence quickly when you are tired or drunk.) Tired people, like drunk people, have a misplaced confidence in their own abilities. This dangerous trait was highlighted in an experiment in which students took cognitive tests after they had been deprived of sleep for 24 hours. Predictably, they performed worse than subjects who had slept well the night before. However, when asked to assess their own performance, the sleep-deprived subjects awarded themselves higher ratings than did the non-deprived subjects. Tiredness had marred their ability to appreciate their own inability.
Cultural attitudes towards being tired or drunk behind the wheel of a car are very different, despite the fact that the net outcomes are remarkably similar and sometimes fatal. Driving when drunk is illegal and (nowadays) socially unacceptable, whereas driving when tired is neither. People still boast about their feats of sleep-deprived driving, in the way that people once boasted of their ability to drive after downing stupefying quantities of booze. Of course, one big difference between drinking alcohol and going without sleep is that drinking alcohol is enjoyable. Sleep deprivation has only the bad bits to offer, including the hangover.
Being tired and drinking alcohol are obviously not mutually exclusive. Indeed, the two often go hand in hand. A night on the town is often a night of little sleep. What is more, they reinforce each other. Tiredness amplifies the effects of alcohol and vice versa. It is a common experience (except presumably among lifelong teetotallers) that alcohol packs a heftier punch when we are tired – say, at the end of a hectic working week. Even moderate amounts of alcohol produce a big sedative effect after insufficient sleep. Conversely, the effects of alcohol are somewhat blunted if you are well rested. Experiments have found that alcohol reduces the alertness of people who have had less than eight hours’ sleep the previous night, whereas the same amount of alcohol makes no difference if they have had unlimited sleep. If you want to enjoy a few drinks without wilting, make sure you sleep properly the night before.
Another common experience is that the effects of alcohol vary according to the time of day when it is drunk. This happens because alcohol reinforces our natural circadian rhythm in sleepiness, exaggerating the troughs in alertness that normally occur in the early hours of the morning and again in the afternoon. Alcohol consumed at lunchtime or in the early afternoon therefore tends to have a bigger impact than the same amount consumed in the early evening, when alertness is normally higher. Lunchtime boozing really is more likely to make you fall asleep at your desk or crash your car than those pre-dinner ‘sharpeners’.
Scientists have also uncovered some intriguing parallels between sleep deprivation and the normal ageing process. As we grow older, our performance declines on many psychological and neurological measures. A similar pattern of deterioration is observed in young people after sleep deprivation. One experiment found that after 36 hours without sleep, adults in their twenties had a performance profile similar to that of non-sleep-deprived people aged about 60. So, if you are in your twenties and you want to know how it feels to have the brain of a healthy 60-year-old, just stay up all night. Then you will know. The reason why ageing and sleep deprivation exert similar effects may be because they both impair the functioning of the prefrontal cortex, a region of your brain that is extremely active when you are awake.
To complete the three-way permutation, alcohol and old age make an unpleasant cocktail. Being old is generally bad for sleep, and so is being an alcoholic. Being old and alcoholic is even worse. The elderly are more prone to insomnia, as we shall see in a later chapter. Alcoholism is also accompanied by sleep problems. And when old age and alcoholism combine within the same person they reinforce their malign influences on sleep. Researchers have found that older alcoholics have significantly worse sleep problems than younger alcoholics.
Sleep, or lack of it, can also affect physical appearance – a belief encapsulated in the term ‘beauty sleep’. Although sleeping all hours will not necessarily make you more beautiful, prolonged lack of sleep will detract from your physical charms. Animals that have been experimentally deprived of sleep for long periods develop unsightly skin disorders. Lack of sleep in humans, especially adolescents and young adults, might exacerbate skin problems such as acne. Sleep deprivation weakens the ability of the skin to maintain its normal protective functions as a barrier against dirt and microbes. That said, the scientific evidence for a direct causal link between sleep and an unblemished complexion remains sparse, Sleeping Beauty notwithstanding.
Lack of sleep probably does contribute to the depressing tendency of men to become pot-bellied and flabby in middle age. In men (but not women) almost the entire day’s production of growth hormone within the body occurs during sleep. The less sleep a man gets, the less growth hormone his body produces. As part of the normal ageing process, the total amount of sleep and the production of growth hormone both decline in parallel. Scientists have suggested that this age-related fall in growth-hormone production could be responsible for the systematic replacement of muscle by flab, better known as middle-aged spread. If so, dwindling sleep might be an important ingredient in the expanding waistline, double chins and spindly legs that help to make male middle age such a joy.
Champion wakers (#ulink_e5fc89c1-0fd4-554b-af1b-e1faafe93630)
I’ll wake mine eyeballs out.
William Shakespeare, Cymbeline (1609–10)
What happens to people if they get no sleep at all for a long time? One of the first scientific experiments on sleep deprivation dates from 1896, when Professor G. T. W. Patrick and his colleague Dr Allen Gilbert of the Iowa University Psychological Laboratory kept three volunteers awake for 90 hours. Patrick and Gilbert charted the now classic signs of prolonged sleep deprivation, including progressive deteriorations in reactions, memory and sensory acuity, together with a decline in body temperature.
Their first experimental subject, an assistant professor at the university, suffered his worst fatigue during the second night. Like Charles Lindbergh, he found that dawn was the cruellest time. He experienced visual hallucinations in which the air seemed full of red, purple and black dancing particles like gnats. All three subjects gained weight during the experiment, but their muscular strength diminished as they became more fatigued. The most noticeable effects were on mental performance: their memory became highly defective and they lost their ability to pay attention. One subject failed to memorise in 20 minutes material that he would normally have committed to memory in two minutes. In all cases, the symptoms disappeared after the experiment.
The first person to become internationally famous for self-imposed sleep deprivation was an American disc jockey called Peter Tripp, whose other claim to fame was inventing the Top 40. In 1959, Tripp managed the feat of staying awake under supervision for more than eight days and nights, a total of 201 hours. He did it to raise money for charity. Tripp even managed to broadcast live during his marathon, from a booth in Times Square, New York.
Peter Tripp suffered. As time went on, his friends and invigilators found it harder and harder to keep him awake. Constant vigilance was required to prevent him from lapsing into microsleeps. Three days into the experiment, Tripp became abusive and unpleasant. After the fifth day he progressively lost his grip on reality and started to experience visual and auditory hallucinations. His dreams broke through into his waking thoughts and he began seeing spiders in his shoes. He became paranoid and thought people were drugging his food. At one point he ran into the street and was nearly knocked down. These disturbing psychological symptoms were accompanied by physical changes, including a continuous decline in body temperature. By the last evening, Tripp’s brain-wave patterns were virtually indistinguishable from those of a sleeping person, even though he was apparently still awake.
After 201 hours of continuous wakefulness Tripp had broken the record and halted the experiment. He immediately fell into a deep sleep that lasted 24 hours. When he finally did awake, his hallucinations had gone and he felt relatively normal. But something seemed to have changed within him. Those close to Peter Tripp felt his personality had altered permanently, and for the worse. His wife left him, Tripp lost his job and he became a drifter. Tripp’s marathon of sleep deprivation certainly did him no good, but it was probably not the sole cause of his subsequent decline and fall. Tripp was taking large doses of Ritalin, an amphetamine-like stimulant drug, to keep himself awake during the marathon, and it is possible that the drug, combined with the sleep deprivation, helped to stimulate his paranoid delusions and hallucinations.
A few years later, Tripp’s record was broken by a 17-year-old high-school student from San Diego called Randy Gardner. In 1965 Gardner stayed awake for 264 hours (or 11 days) in a successful attempt to break into The Guinness Book of Records. Scientists from Stanford University monitored most of his marathon. During the first two days Gardner’s friends helped keep him awake and he did not use caffeine or other stimulants. By the end of the second day he was suffering from blurred vision, making it difficult for him to read or watch TV. By the third day he was irritable and wanted to be left on his own. His speech became slurred and his movements uncoordinated. On the fourth day he experienced memory lapses and mild hallucinations. After nine days without sleep he was unable to complete sentences and had lost the ability to concentrate. On the eleventh and final evening he had double vision.
Despite these temporary but unpleasant symptoms, Randy Gardner suffered remarkably few ill effects. Having stayed awake for 11 days and nights, he went to bed and slept for nearly 15 hours. When he awoke he felt fine. The following night he slept only slightly longer than usual, and within a few days his sleep had returned to normal. He did not go mad and, except for mild hallucinations, he never displayed any psychotic symptoms during the experiment. The experiences of Randy Gardner and others have demonstrated that going without sleep for several days does not generally result in mental illness or other long-term damage.
Some feats of self-imposed sleep deprivation have been endured for purely financial reasons, with not a single scientist in sight. In the depression-era USA of the 1920s and 1930s, a bizarre fad developed for dance marathons, in which people would compete for money. The rules were simple: keep dancing until you drop. This grisly social phenomenon was portrayed in the 1969 film They Shoot Horses, Don’t They? The dance-marathon competitors were supposed not to sleep, although some competitions permitted one dancer to sleep provided their partner held them upright and both kept moving. They must have slept while dancing, since it was not uncommon for these nightmarish marathons to last for weeks. The world record was set by a couple in Chicago, who danced from 29 August 1930 until 1 April 1931 – a total of almost 215 days. The rules allowed them to close their eyes for no more than 15 seconds at a time, so they must have been adept at sleeping with their eyes open. Their reward for this outlandish spectacle of public torture was a paltry $2,000. These dance marathons were eventually made illegal. And talking of torture, let us turn to that uncomfortable subject.
Uses and abuses (#ulink_0b8fe922-fa98-5f44-9299-cafadeada523)
It was always at night – the arrests invariably happened at night. The sudden jerk out of sleep, the rough hand shaking your shoulder, the lights glaring in your eyes, the ring of hard faces round the bed. In the vast majority of cases there was no trial, no report of the arrest. People simply disappeared, always during the night.
George Orwell, Nineteen Eighty-Four (1949)
Sleep deprivation is unpleasant and debilitating. Someone who has not slept for two or three days can feel as if they are losing their mind. That is why, throughout history, sleep deprivation has been exploited as a form of torture and coercion. Fatigue can bring people to their knees, both metaphorically and literally, without leaving a mark on them. It can even be fatal.
According to legend, King Perseus of Macedonia was put to death by being prevented from sleeping when held prisoner in Rome. Sleep deprivation is also said to have been a form of capital punishment in China in times past. The American writer and insomniac Bill Hayes cites a nineteenth-century account of a Chinese merchant who was sentenced to death for murdering his wife. Sleep deprivation was deliberately chosen as the method of execution, on the grounds that it would cause the maximum amount of suffering and would therefore serve as the greatest deterrent to other potential murderers. According to the account, which was written by an American physician, the prisoner eventually died on the nineteenth day, having suffered appalling torment.
Sleep deprivation has been employed for many centuries to soften up prisoners and make them talk. And it still is. Amnesty International found that more than half the torture victims they interviewed had been deprived of sleep for at least 24 hours. The secret police notoriously prefer to make their arrests in the small hours of the morningbecause that is when people are at their weakest and most confused.
When applied patiently and systematically, sleep deprivation is said to be the single most effective form of coercion. The victim is repeatedly woken at odd hours, allowing them little or no sleep. The pattern of awakenings is randomised, so the victim loses all control over when they sleep (an extreme version of what happens to parents of small babies). This unpredictability makes it impossible for the body’s internal clocks to readjust. The circadian rhythms become disrupted, leaving the victim fatigued and in a state akin to severe jet lag. All sense of time and place depart. Even the strongest person can be reduced in this way to a state of helpless and tearful disorientation.
Exhausted people are very poor at making sound judgments based on complex information, including information derived from their own knowledge, beliefs and experience. Sleep-deprived prisoners are therefore much more susceptible to persuasion that their actions or beliefs are wrong. Herein lies the secret of ‘brainwashing’.
In the Korean War of 1950–53, the Communists tortured American and Allied prisoners of war by systematically depriving them of sleep. A constant succession of guards would interrogate a prisoner at random times throughout the day and night, subjecting him to a constant barrage of questions and arguments. The effects on prisoners’ behaviour and beliefs were often profound. Sixty per cent of the US airmen who were captured in the Korean War either confessed to imaginary crimes, such as using biological weapons, or collaborated with the enemy in condemning the USA. When the prisoners were eventually returned to the USA, the US government appointed a panel of experts to discover what had happened. The assumption at the time was that the Communists must have subjected the Allied prisoners to some mysterious and sophisticated form of mind control. Either that, or the men must be traitors and cowards. But the evidence uncovered by the review panel ruled out drugs, hypnosis or other forms of novel trickery. The truth was more prosaic. Just one device had been used to confuse and torment the prisoners until they were ready to confess to anything. That device was prolonged sleep deprivation. A combination of fatigue, confusion, fear and loss of control had produced profound changes in the men.
The practice of sleep-depriving military prisoners continues to this day. In April 2001 a US military surveillance aircraft collided in midair with a Chinese fighter. The American plane was forced to make an emergency landing in China. Meanwhile, the Chinese plane crashed, killing the pilot. The Chinese authorities were not happy: they impounded the American plane along with its crew of 24, sparking a diplomatic row between the two nations. The crew were eventually released after being detained and questioned for 11 days. They later revealed that the Chinese had used sleep deprivation as part of the interrogation process. The American pilot reported that the Chinese had questioned him for several hours on the first night, and thereafter had repeatedly woken him at various times of the night and day, forcing him to snatch a little sleep whenever he could.
Prolonged sleep deprivation lay behind many of the psychiatric casualties of World War One. Thousands of men had to be withdrawn from the horrific conditions of the front line with what was referred to then as shell shock. (Nowadays we would call it post-traumatic stress disorder.) Continuous shelling was undoubtedly a cause of severe stress. For hours or days at a time, men crouched defenceless in muddy trenches, constantly exposed to the threat of instant death or injury but powerless to do anything about it. Even the hardiest of minds could crack. But the shelling broke men for another reason as well: it prevented them from sleeping. Doctors often found that when a man with disabling shell shock was granted respite from the front line, he would rapidly recover and be able to return to his unit within days. Getting a few nights’ sleep in the hospital probably did more good than the psychotherapy that went with it.
When we starve ourselves of sleep in the name of work or play, we go partway down a path that leads eventually to something horrific.
4 The Golden Chain (#ulink_81a2ff50-c972-55a6-b9fe-5b3aa2d2ff90)
Sleep is that golden chain that ties health and our bodies together.
Thomas Dekker, The Guls Horn Book (1609)
We have seen some of the bad things that sleep deprivation does to our minds. What does it do to our bodies? Sleep and physical health are intimately intertwined, which means that inadequate sleep can cause all sorts of physical problems. When sleep deprivation is taken to the extreme, death ensues. Some scientists have argued that many of us neglect or mismanage our sleep to the extent that it damages our health, and that large numbers of people around the world die prematurely every year because of undiagnosed and untreated sleep disorders.
What, then, is the scientific evidence that sleep impinges on our physical health? Some (admittedly crude) indicators point towards a link between poor sleep and poor physical health. For instance, people who are sleepy during the day are more likely to use healthcare. And older people who complain of poor sleep are at greater risk of a heart attack. One American study that tracked thousands of elderly people discovered that individuals with sleep problems were more likely to suffer a heart attack over the following three years.
Lack of sleep and the resulting daytime tiredness are associated with greater sickness absence from work. An investigation of absenteeism among French employees found that those who reported feeling very sleepy at least three days a week were more than twice as likely to take sick leave as their less sleepy colleagues. Sleep problems are also predictive of long-term work disability. Norwegian research found that adults who were experiencing mediocre or poor sleep were more than twice as likely to face long-term work disability a few years later. People who sleep badly also tend to eat badly, which may contribute to their health problems.
Good sleep, on the other hand, fosters mental and physical health. Psychological wellbeing, physical health and longevity are all statistically associated with healthy lifestyle practices, one of which is good sleep. The lifestyle factors associated with a lower risk of dying prematurely include taking physical exercise, not smoking and getting seven or eight hours of sleep a night. For example, recent research that investigated longevity in Japanese people uncovered three important factors, each of which was independently linked with a reduced risk of dying. These factors were walking for at least one hour a day, ikigai (a sense that your life is meaningful), and sleeping for at least seven hours a night. There is even some tentative evidence that people who habitually go to bed early live longer. A study of people aged over 80 found that these long-lived individuals all reported having gone to bed early throughout their lives. However, retrospective evidence of this sort must always be taken with a large pinch of salt. (But not too much salt, because that would be unhealthy.)
At the other extreme, excessive sleep is also linked statistically with poor health – probably because sleeping for unusually long periods is often a sign of illness. Scientists discovered in the 1970s that people whose normal nightly sleep duration was either unusually short (less than four hours) or unusually long (more than nine or ten hours) had a higher than average risk of dying prematurely. Similarly, a study of elderly British people found that those who spent 12 or more hours a day in bed had a significantly higher mortality rate, while those who spent the proverbial eight hours a day in bed had the lowest mortality rate.
Excessively long sleep is often a consequence of heart disease or other medical conditions, so it would be a mistake to generalise this finding very far. There is no reason to suppose, for example, that sleep-deprived teenagers or exhausted adults who lie in bed at the weekends will die younger as a consequence of snatching a few extra hours of rest. Too much sleep can make you feel temporarily below par, however. Experiments have confirmed that healthy people who normally feel refreshed after eight hours of sleep tend to feel groggy and perform badly after they have slept (on request) for 10 or 11 hours. On the other hand, how many healthy adults routinely sleep for 10 or 11 hours at a time? Few of us have any reason to fret about the dangers of sleeping too much.
A waking death (#ulink_ea5ea79a-df58-5457-ae6f-14f5b69f2eaa)
We term sleep a death, and yet it is waking that kills us, and destroys those spirits that are the house of life.
Sir Thomas Browne, Religio Medici (1642)
What happens when sleep deprivation is taken to the extreme? If a slight insufficiency of sleep makes us feel unwell, would a prolonged absence kill us? Setting aside purely anecdotal accounts, science has unsurprisingly not investigated whether forcibly depriving humans of sleep is fatal. Ethical committees would tend to frown upon applications from scientists proposing to test this experimentally. But the evidence from other species is clear. Animals that have been experimentally deprived of sleep for long enough invariably die. There is no reason to suppose that humans are fundamentally different.
Some of the earliest experiments on extreme sleep deprivation were performed in the late nineteenth century by a Russian scientist called Marie de Manacéïne. She deprived puppies of sleep by keeping them constantly active. They all died within four or five days, despite every effort to keep them alive. The younger the puppy, the more rapidly it succumbed. Marie de Manacéïne also noticed a progressive decline in the body temperature of the sleep-deprived animals, a phenomenon that is now known to be a standard symptom of prolonged sleep deprivation in humans and other species. She concluded that sleep was even more crucial for survival than food:
As a rule, the puppy deprived of sleep for three or four days presents a more pitiful appearance than one which has passed ten or fifteen days without food. I can speak from observation, as I was obliged to make experiments on the results of want of food as well as of sleep, and I became firmly convinced that sleep is more necessary to animals endowed with consciousness than even food.
Italian scientists working at the end of the nineteenth century kept adult dogs awake by making them walk. The sleep-deprived dogs all died after 9–17 days, regardless of how much food they ate.
One objection to experiments such as these (apart from the obvious ethical one) is that the scientists had to use increasingly stressful methods to keep the animals awake, so perhaps it was the stress that killed them rather than the sleep deprivation itself. Prolonged stress can impair the immune system and make an animal more vulnerable to infection. However, more recent research has managed to sidestep this methodological problem.
In a long series of experiments, Alan Rechtschaffen and colleagues at the University of Chicago systematically investigated how prolonged sleep deprivation affects rats. They used an experimental procedure known as the disc-over-water method, which works like this. Two rats – the experimental subject and the ‘yoked control’ – are placed on a turntable mounted over a shallow bath of water. The brain-wave patterns of both animals are continuously monitored to detect the onset of sleep. When the experimental rat’s brain waves indicate that it is falling asleep, the turntable automatically revolves slowly, waking the unfortunate rat and forcing it to walk in the opposite direction to avoid being pitched into the water. The control animal, which is on the other side of the turntable and separated by a partition, receives precisely the same treatment at precisely the same times. The crucial difference is that the turntable movements are unaffected by its sleep. The control animal is therefore able to get some sleep when the experimental animal is awake. This cunning technique has the advantage – from the human experimenter’s point of view – of preventing the experimental subject from sleeping without having to subject it to other noxious stimuli.
Rats that are prevented in this way from sleeping invariably die after two or three weeks. The control animals, which experience the same stimuli but not the complete loss of sleep, survive and display relatively few symptoms. Before they die, the sleep-deprived rats all exhibit the same horrible syndrome. This is characterised by a debilitated appearance, skin lesions, increased food intake, weight loss, increased metabolic rate, increased levels of the hormone noradrenaline, and declining body temperature. Some of these changes are symptomatic of excessive heat loss from the body, which has led some scientists to suggest that sleep is crucial, among other things, for the regulation of body temperature.
A progressive rise in metabolic rate (the rate at which the body consumes energy) is an early symptom of sleep deprivation. Sleep-deprived rats eat more to compensate for their rising energy expenditure, but their weight and body temperature nonetheless continue to fall. Feeding them an easily digestible diet helps to slow this process somewhat, but it does not prevent them from dying. An increase in appetite is one of the less obvious effects of sleep deprivation in humans as well. Might it be that chronic sleep deprivation is one of the factors helping to fuel the epidemic of obesity that is currently sweeping the USA, UK and other industrialised nations?
Body and soul (#ulink_056f000a-6d8d-504c-a021-e7d92fc8b9f5)
Health may be as much injured by interrupted and insufficient sleep as by luxurious indulgence.
William Kitchiner, The Art of Invigorating and Prolonging Life (1822)
What of people? Research on humans has stopped short of the lethal sleep deprivation imposed on rats and puppies, but it has delved systematically into the consequences of a few days’ sleep loss. The results consistently show that moderate sleep deprivation has pervasive effects on the human body as well as the human mind. Sleep loss impairs vision, for example, causing blurring and errors in judging distances. It also triggers the familiar decline in body temperature that Marie de Manacéïine observed in her puppies, together with a reduction in blood glucose levels and changes in various hormones.
Set against this, sleep loss has surprisingly little impact on our ability to keep moving around and doing physical work. Moderate sleep deprivation does not greatly diminish our capacity for labour. Physically fit young adults can withstand several days of sleep deprivation without a substantial deterioration in their muscle strength, muscle endurance or cardiovascular responses to exercise. In one experiment, for example, the exercise capacity of young women was assessed following 60 hours without sleep. The sleep deprivation had no significant effect on their aerobic capacity or their endurance for exhausting exercise. In another study, researchers monitored two men while they played a marathon tennis match lasting a week, during which time the players got very little sleep. Although their mental performance deteriorated during the match, the players were able to sustain a high level of physical work. Our muscles can mostly keep going even when our brains are flagging.
Sleep deprivation does disturb many aspects of physiological functioning, however. Breathing is one example. A single night of sleep loss impairs breathing in healthy people, provoking a small but significant reduction in the maximum amount of air that can be exhaled after maximum inhalation. Sleep loss also leads to a substantial blunting of the normal respiratory responses to reduced blood-oxygen levels. After 30 hours without sleep there are marked deteriorations in the strength and endurance of the muscles used for breathing – as revealed, for example, by a reduction in the time for which people can breathe in against a sustained pressure. Such changes could be important in patients with respiratory diseases, who often suffer from chronic sleep loss. Sleep deprivation also slows the rate of cardiovascular recovery from intense exercise. When someone has been deprived of sleep for 24 hours, their breathing rate and oxygen uptake after a burst of intense exercise remain higher for longer.
Sleep loss is accompanied by many changes in body chemistry. People who have been kept awake for more than three days have altered liver functions, marked by large increases in the levels of key liver enzymes, changes in various types of fat and a rise in the amount of phosphorus circulating in the blood. Thyroid hormone levels are affected and biochemical changes can be detected at the level of gene activity.
Glucose metabolism is particularly perturbed by sleep loss. Healthy young men whose sleep was experimentally restricted to four hours a night for six nights became less tolerant to glucose. They took 40 per cent longer than normal to regulate their blood-sugar levels after eating high-carbohydrate food, and their ability to produce insulin fell by nearly a third – a condition resembling the early signs of diabetes. These abnormalities vanished after the men had slept for 12 hours. Fatigue-induced physiological changes like these could contribute to the development of chronic conditions such as diabetes, obesity and high blood pressure, all of which are associated with a shortened lifespan.
Sleep, immunity and health (#ulink_1f2df845-d1fc-5f97-86ab-ea2ec9fcf366)
Our foster-nurse of nature is repose.
William Shakespeare, King Lear (1605–6)
Some of the most interesting, least well understood, and potentially important consequences of sleep deprivation are found within the immune system. In short, lack of sleep can impair the body’s immune defences and thereby make us more susceptible to infection by bacteria, viruses and parasites.
The evidence comes mostly from research with other species. In one experiment, for example, mice that were immunised against the influenza virus were resistant to infection if they were exposed again to the virus a week later. But if the immunised mice were deprived of sleep for seven hours immediately after being exposed to the virus, they were no more resistant to infection than mice that had not been immunised at all. A mere seven hours of sleep deprivation disturbed their immune response enough to erase the benefits of immunisation.
Some scientists have suggested that one reason why prolonged sleep deprivation is ultimately fatal is that it breaks down the animal’s immune defences, making it vulnerable to infection by any opportunistic bacteria and viruses that happen to be in the vicinity. Experiments with rats have shown that following severe sleep deprivation, the lymph nodes and other organs are invaded by potentially dangerous bacteria, which appear to have migrated there from the intestines. However, the role of infection in killing sleep-deprived animals remains a controversial issue.
Sleep loss impairs the human immune system as well. Even modest sleep deprivation evokes measurable changes. One night of sleep loss lowers the activity of natural killer cells and reduces the numbers of several different types of white blood cells circulating in the bloodstream. (Natural killer cells are a special type of lymphocyte, or white blood cell, that attack virus-infected cells and certain types of cancer cells.) Depriving healthy adults of sleep for seven hours on one night suppressed their natural killer-cell activity by 28 per cent. It bounced back to normal after a night of uninterrupted sleep. Moderate sleep loss will also reduce the body’s production of interleukin-2, a chemical messenger substance that plays an important role in regulating immune responses. After two or three days of sleep deprivation there is a marked decline in the responsiveness of lymphocytes and an even bigger fall in the activity of natural killer cells.
Sleep loss might play a role in the well-established connection between severe depression and impaired immune function. Depressed people generally sleep badly and have poorer immune responses. The more disrupted their sleep, the bigger the decline in their immune function. One study, for example, found that people who were suffering from depression following bereavement had fewer natural killer cells. The bereaved subjects were troubled by intrusive thoughts that often woke them or kept them awake during the night. The extent of the reduction in their natural killer-cell numbers was correlated with the amount of time they spent awake during the night: the more troubled someone was by their loss, the more disrupted their sleep and the fewer natural killer cells circulating in their blood. Sleep deprivation could be one of the mechanisms by which depression makes people more vulnerable to illness.
The relationship between sleep and immunity works in both directions. Not only does sleep affect the immune system, but the immune system also affects sleep. The immune reactions triggered by infection and illness can elicit alterations in sleep patterns. That is why infections are often accompanied by lethargy, loss of appetite, depressed mood and general malaise. Animals infected with influenza virus display a large increase in sleep about 24 hours after exposure to the virus. These changes in wakefulness are part of the body’s defence mechanisms and assist the recovery process. Human experiments, in which noble volunteers were injected with bacterial toxins, found that sleep is highly sensitive to the activation of the immune defences. Low-level infection tends to promote deep sleep. However, a full-blown infection accompanied by fever induces lethargy but typically disrupts sleep. You might have noticed that you sleep more deeply for a night or two when your body is fending off a potential infection, whereas when you are in the throes of a galloping illness you feel exhausted but lie for hours without sleeping.
The immune response to infection stimulates the release of chemical messenger substances that act on the brain to induce malaise, drowsiness, loss of appetite and sleep. During infection, a substance known as interleukin-1 stimulates the brain to induce deep sleep, while other interleukins trigger the fever that often accompanies infections. They do this by adjusting the brain’s temperature control centres – in effect, putting the body’s thermostat on a higher setting. That is why we feel hot and sleepy when we have a bad infection. The fever response is a defence mechanism found in all animals: the rise in body temperature makes life harder for the offending bacteria or viruses, and the lethargy forces the infected organism to curl up in a dark corner and sleep until it has recovered. It all makes good biological sense.
The brain and the immune system are interconnected through an elaborate network of chemical and neural communication channels. One important link between sleep, immune function and psychological stress is the steroid hormone cortisol. Sleep deprivation and prolonged stress both provoke an increase in the level of cortisol. After one night of sleep loss, your cortisol levels would typically be raised by about 45 per cent the next evening. It is not good to have elevated cortisol levels for too long, since cortisol has a powerful suppressive effect on the immune system. The functioning of the immune system is also intimately bound up with the 24-hour sleep – wake cycle and the circadian rhythms in hormone levels. Various aspects of immune function fluctuate in tune with the circadian cycle. Anything that disrupts the normal cycle of sleep and wakefulness therefore tends to disturb the immune system, with potential consequences for the body’s ability to defend itself against infection and disease.
The intimate relationship between sleep and immune function takes on a potentially huge practical significance when you consider how widespread sleep deprivation has become in society. Tired people are more likely to become sick people.
The Battle of Stalingrad (#ulink_9b00653d-4c92-584b-bd9a-f2e3f6199cb4)
O, I have passed a miserable night,
So full of fearful dreams, of ugly sights
William Shakespeare, Richard III (1591)
Prolonged sleep deprivation, uncontrollable stress and starvation make a lethal cocktail, as Hitler’s troops found to their cost during the Battle of Stalingrad in World War Two. In June 1941 German forces invaded the Soviet Union and were soon threatening Moscow. The capture of Stalingrad on the River Volga became a key strategic objective. Stalin decreed that the city must be defended to the bitter end. The titanic struggle that ensued cost the lives of at least 800,000 Axis soldiers and 1.1 million Soviet soldiers.
The fight for Stalingrad (now renamed Volgograd) began in earnest in the summer of 1942, as the Germans advanced rapidly towards its suburbs. There was fierce Soviet resistance and the fighting dragged on into the harsh Russian winter. By September 1942 the battle was being waged at close quarters among the buildings, cellars, sewers and bunkers of ‘the Stalingrad Academy of street-fighting’.
To increase the pressure on their opponents, the Soviet commanders ordered continual raids to be carried out by night. They did this partly because the Germans lacked protection from their air force at night, but mainly to induce exhaustion among the enemy. To augment the night raids, the Soviets fired flares indicating that an attack was imminent even when it was not. Their air force also attacked German positions every night. The Soviets kept up the psychological pressure throughout the night, with loudspeakers blaring out propaganda broadcasts, surreal tango music, or the sound of a ticking clock. The strategy was highly effective. ‘We lie exhausted in our holes waiting for them,’ wrote one German soldier. The German commanders begged for air support, citing their men’s exhaustion.
The German troops’ health started to deteriorate badly even before the dreadful Russian winter had begun to bite. There was a sharp rise in deaths from infectious diseases including dysentery, typhus and paratyphus. The actual prevalence of these diseases was not much worse than it had been a year earlier, but the numbers of infected men who were dying from them increased fivefold. It was as though the German soldiers had lost their capacity to resist infection. The Russians noticed this phenomenon, which they referred to as ‘the German sickness’.
In November 1942 the Russians launched a huge and ultimately successful counteroffensive that soon had the Germans encircled within the ruined city. But the Germans were under orders from Hitler not to surrender, and so they fought on through December while the Russians gradually tightened the noose. Conditions for the German troops became appalling as their supply lines were cut off and the Russian winter froze them. There was hardly any food and little or no medical care.
In mid-December 1942 the German military doctors in Stalingrad noticed a new phenomenon: more and more apparently healthy troops were suddenly dying for no obvious reason. The Germans were unsure whether the deaths were the result of starvation, exposure, exhaustion or an unidentified disease. A German army pathologist named Girgensohn, who was sent to Stalingrad to investigate the problem, became convinced that a combination of exhaustion, stress, cold and lack of food was responsible for the much higher death rate. The Russian night attacks and round-the-clock activity had caused severe sleep deprivation, and Girgensohn concluded that this had amplified the effects of the food shortage by ‘upsetting the metabolism’ of the exhausted Germans. We know now that one symptom of prolonged sleep deprivation is a marked increase in metabolic rate and hence the requirement for food. Whatever the precise explanation, the pressure was too much for the Germans. In February 1943 the Battle of Stalingrad finally ground to a halt, as the crushed and starving remnants of the German army surrendered.
Sleepless in hospital (#ulink_970a2ca6-868e-5135-aa5d-1fce1f4248e3)
I have the feeling that once I am at home again I shall need to sleep three weeks on end to get rested from the rest I have had.
Thomas Mann, The Magic Mountain (1924)
Sleep is good for you and lack of sleep is bad. It therefore seems odd that hospitals, which are supposed to promote recovery, are usually dreadful environments for sleeping. ‘The hospital bed,’ wrote one historian, ‘is one in which normal sleep is forbidden.’ A Punch cartoon of 1906 shows a patient being told to ‘wake up and take your sleeping-draught’. Things have improved since 1906, but not much.
Sick people really do benefit from sleep. We saw earlier how the brain and the immune system respond naturally to infection by inducing sleep. This helps the body cope with disease in several ways. The production of growth hormone occurs mainly during sleep, and growth hormone aids physical recovery by promoting the healing of mucous membranes and in other ways. The hormone melatonin, which is also produced at night, boosts immune responses, inhibits the growth of tumours and enhances resistance to viral infections. Conversely, sleep deprivation impairs immunity and slows the healing process. Given the importance of sleep for recovery, it is ironic that hospital patients are routinely subjected to conditions that make normal sleep almost impossible.
Sick people start with big disadvantages, of course. Pain is a powerful disrupter of sleep. Patients suffering from chronic, severe pain often become exhausted. Disrupted sleep is a common complication of burn injuries, for example. Studies have found that between half and three quarters of burns patients experience significant sleep disturbances. Sleep problems are common among cancer patients too. Fatigue can become one of the most distressing aspects of having cancer, severely reducing the quality of life. While medical treatments for cancer have advanced apace, efforts to improve patients’ quality of life by alleviating their fatigue have lagged behind.
To make matters worse, tired people are more sensitive to pain. Sleep deprivation lowers pain thresholds, generating a vicious cycle in which pain disrupts sleep, the resulting sleep loss makes the pain feel even worse, and so on. An investigation of patients with burns injuries uncovered a systematic link between the quality of their sleep and subsequent pain. Patients who slept poorly during the night experienced more intense pain the following day, because the fatigue intensified their perception of pain.
One of the worst places imaginable if you need a good night’s sleep is an intensive care unit (ICU). The combination of serious illness, serious drugs, constant monitoring, bright lighting and the aftereffects of surgery ensures that ICU patients are often subjected to severe sleep deprivation. And yet the ICU houses the sickest people in the hospital, with the greatest need for sleep. American researchers conducted an experiment to see if implementing regular ‘quiet times’ during the day would help ICU patients to get more sleep. Each day for two two-hour periods, lighting levels in the unit were reduced and the staff made a concerted effort to minimise noise. The ‘quiet-time’ regime worked: the patients were 60 per cent more likely to sleep during these quiet periods than at other times of the day. More flexibility over when patients are given their medication can also help them to get more sleep.
Sadly, the apparent neglect of sleep in hospitals is another reflection of the general disregard for sleep in medicine and society as a whole. Lack of sleep really does have very little to recommend it.
PART III Mechanisms (#ulink_be9ab661-a886-5eee-a451-329f6d4fd927)
5 The Shapes of Sleep (#ulink_70b8113c-3786-5379-a11c-7351d23b0377)
Sleep rock thy brain.
William Shakespeare, Hamlet (1601)
Now it is time to peer beneath the surface at the strange state of existence known as sleep – or, to be more precise, the two strange states of existence known as sleep.
All of human life is spent in one of three states. You are very familiar with one of them: it is called the waking state, or consciousness, and it forms the subject matter for almost everything that has ever been said, written, acted, painted or composed about humanity. When scientists analyse the mind, when novelists dissect the human condition and when biographers portray the lives of eminent individuals, it is the waking state they almost invariably describe. However, there are two other distinct states of existence that together account for at least a third of each life. They labour under the workaday names of Rapid Eye Movement (REM) sleep and Non-Rapid Eye Movement (NREM) sleep, and we are about to take a closer look at them.
A night’s sleep is a complex and cyclic process, comprising several distinct patterns of brain activity and behaviour, with alternating episodes of NREM sleep and REM sleep. We will follow the sleep cycle from the beginning, starting with the transition from the waking state. But before we do that, a quick word about how scientists know what is going on when we are asleep.
Measuring sleep (#ulink_1726e0c8-aadf-5969-b848-c38cd4d3615b)
Brains wave.
Owen Flanagan, Dreaming Souls (2000)
The sleeping brain reveals what is going on inside itself in various ways, both electrically and chemically. Since the middle of the twentieth century, the main tool for monitoring sleep has been the electroencephalograph. This machine exploits the fortunate fact that varying patterns of electrical activity within the brain manifest themselves as varying patterns of voltage changes on the surface of the scalp.
The brain comprises billions of nerve cells, or neurons, and although the electrical activity of an individual neuron is too faint to be detected outside the skull, it is possible to monitor the gross patterns generated collectively by large numbers of neurons. These show up as minute voltage changes, which can be detected by electrodes stuck onto the scalp. (The very first electrodes were small pins that were stuck into the scalps of stoical volunteers.) Thus, the brain emits electrical signals revealing information about its inner state. These tiny voltage patterns are amplified and displayed as the familiar ‘brain waves’ of the electroencephalogram, or EEG. (Confusingly, the machine is called an electroencephalograph, while the graph it produces is called an electroencephalogram, or EEG. To avoid nausea, I will use EEG to denote both the machine and its output.)
The EEG was invented in the 1920s by a psychiatrist named Hans Berger. It really came into its own in the 1950s when, as we shall see, it enabled the discovery of REM sleep. Before the invention of the EEG, scientists could only assess sleep by observing overt body movements, or the lack of them. Scientists still find it useful to record sleepers’ body movements, especially in studies of sleep patterns under natural conditions where the use of EEG would be too intrusive or too expensive. Nowadays, body movements are usually logged automatically, using a miniature recorder worn on the wrist.
Sleep laboratories use an extension of the EEG called the polysomnograph – a sort of somnolent variation on the polygraph. A polysomnograph records the EEG brain waves, together with other informative measures of the sleeper’s physiological state and behaviour. Electrodes placed near the corners of the eyes detect movements of the eyeballs, producing a trace known as the electro-oculogram, or EOG. Other electrodes placed on the chin and neck monitor the muscle tone (producing an electromyogram, or EMG) while electrodes on the chest record the heart rhythms (electrocardiogram, or ECG). Additional devices may record whole body movements, breathing, the flow of air through the nose and mouth, and the concentration of oxygen in the blood. In the early days of sleep science, these measurements were recorded as continuous pen traces on miles of rapidly unfurling paper, but nowadays the outputs are usually stored digitally.
In recent decades, brain scanning has become an increasingly important tool in sleep research. One of the main brain-scanning techniques is called positron emission tomography (PET). PET scans reveal the local patterns of blood flow and oxygen uptake within small areas of the brain by measuring how rapidly the tissue is using energy. Unlike some brain-scanning techniques, PET does not require the subject to sleep inside a large, claustrophobia-inducing scanning device. It therefore allows scientists to monitor sleep under conditions that are slightly closer to normality. Even so, the sleeping subject’s head needs to be kept absolutely still, which is usually achieved by pinning the head down with a special mask (the stuff of some people’s nightmares).
Most measurements of sleep are made in specialised sleep laboratories rather than people’s own homes. The underlying assumption is that the sleep patterns observed in the laboratory closely resemble the real thing. Fortunately, this turns out to be a broadly valid assumption. Comparisons have confirmed that for most people there is a reasonably good concordance between their sleep patterns at home and in the sleep laboratory. But there are some systematic differences. In particular, people tend to sleep for a slightly shorter period under laboratory conditions and to wake up slightly earlier than they would normally. They also have less bizarre dreams and fewer wet dreams. (Wouldn’t you?)
Falling asleep again, what am I to do? (#ulink_b330ab61-a9f6-5a33-a7d6-2ff7e618681b)
Warm beds: warm full blooded life.
James Joyce, Ulysses (1922)
Falling asleep is not an abrupt process, like turning off a light, although it can seem like that because you usually forget about it. Recordings of brain-wave activity and other physiological variables show that falling asleep is in fact a continuous process, which starts from a state of relaxed drowsiness and ends in the first or second stages of unequivocal sleep.
During that process of falling asleep you may find yourself temporarily suspended for several minutes between the worlds of waking consciousness and sleep. This transition phase is often accompanied by strange thoughts, dreamlike images and occasional hallucinations. In one of his short stories, Washington Irving described how the mind can roam far and wide while it is in this pre-sleep state:
My uncle lay with his eyes half closed, and his nightcap drawn almost down to his nose. His fancy was already wandering, and began to mingle up the present scene with the crater of Vesuvius, the French Opera, the Coliseum at Rome, Dolly’s Chop house in London, and all the farrago of noted places with which the brain of a traveller is crammed – in a word, he was just falling asleep.
These dreamlike experiences occur when we are in what is known as the hypnagogic state – a twilight zone partway between wakefulness and sleep. They are referred to as hypnagogic (or sleep-onset) dreams and they are distinct from ordinary dreams, which do not occur until much later in the sleep cycle. Hypnagogic dreams can contain all the basic elements of ordinary dreams, including bizarre plots, visual images and sounds, but there are fewer of these features in any one dream, suggesting that hypnagogic dreaming is a reduced version of normal dreaming. Similar dreamlike experiences can also occur at the other end of a night’s sleep, during the transition from sleep to wakefulness, when they are known as hypnopompic dreams.
The hypnagogic and hypnopompic states are strange and fascinating. In comparison with true sleep and ordinary dreams, they are also poorly researched and poorly understood. Indeed, the English language does not even have a decent name for them – unlike Italian, which has a single word for both (dormiveglia, or ‘sleep-waking’). In English, hypnagogic dreams are colloquially referred to by a variety of vague terms such as ‘faces in the dark’ or ‘visions of half-asleep’. As we shall see in a later chapter, many famous creative flashes and inspired thoughts have come to people while in the hypnagogic state.
During hypnagogic dreams we may see strange sights, hear strange sounds and think strange thoughts. As our wakefulness fluctuates, we may wake up again and consciously remember the strange things we have briefly been dreaming. This hypnagogic nonsense sometimes includes bizarre, invented words. The sleep researcher Ian Oswald recalled waking from one hypnagogic dream with the phrase ‘or squawns of medication allow me to ungather’ running through his mind. On another occasion he found himself musing on the hypnagogic thought that ‘it’s rather indoctrinecal’. A British magazine once printed a collection of hypnagogic ramblings sent in by readers. These included the immortal verse ‘Only God and Henry Ford have no umbilical cord.’
Hypnagogic thoughts and images can be more coherent, however. Charles Dickens often fell into a half-sleeping state while on one of his long nocturnal walks, and he could compose poetry while in this reverie. Dickens wrote of how, one night, he got out of bed at two in the morning and walked thirty miles into the countryside:
I fell asleep to the monotonous sound of my own feet, doing their regular four miles an hour. Mile after mile I walked, without the slightest sense of exertion, dozing heavily and dreaming constantly … It is a curiosity of broken sleep that I made immense quantities of verses on that pedestrian occasion (of course I never make any when I am in my right senses), and that I spoke a certain language once pretty familiar to me, but which I have nearly forgotten from disuse, with fluency. Of both these phenomena I have such frequent experience in the state between sleeping and waking, that I sometimes argue with myself that I know I cannot be awake, for, if I were, I should not be half so ready.
People who play lots of computer games sometimes experience ‘screen dreams’ as they fall asleep, in which they see vivid images of the game they have been playing. These screen dreams are also products of the hypnagogic state. The computer game Tetris, which requires the player to fit together coloured shapes as they cascade down the screen, is well known for provoking hypnagogic dreams. Scientists at Harvard Medical School investigated screen dreams by getting volunteers to play Tetris for several hours. Many of them experienced vivid dreams about Tetris as they fell asleep. Among the subjects in this experiment were five amnesiac patients who had extensive brain damage in their temporal medial lobes – brain regions crucial for conscious memory. Three of the five amnesiacs experienced hypnagogic dreams of Tetris even though they had no conscious memory of playing the game. This implies that the brain can generate hypnagogic dreams without input from conscious memory.
The length of time it takes you to fall asleep, once you have lain down and shut your eyes, is known as your sleep latency. It varies according to lots of factors. As we saw earlier, very short sleep latencies usually indicate sleep deprivation, whereas very long sleep latencies may signify other problems. A study of people living in rural Oxfordshire found that those with the longest sleep latencies typically described themselves as bored or mildly ill. You can make yourself fall asleep faster if you are minded to do so. Researchers proved this by giving volunteers a financial incentive to fall asleep quickly at various times during the day. The paid volunteers fell asleep faster than subjects who had no financial incentive.
Your body temperature has a big influence on how fast you fall asleep. A night’s sleep is normally preceded by a drop in core body temperature, and scientists have established that this drop in temperature actively facilitates the onset of sleep. Under normal conditions, the maximum rate of decrease in body temperature occurs about one hour before the onset of sleep. If the onset of sleep is artificially delayed, the drop in body temperature is attenuated – further evidence that the two are closely linked. The polymath Benjamin Franklin realised the importance of a falling body temperature in triggering sleep. He set out this practical advice in a 1786 essay called ‘The Art of Procuring Pleasant Dreams’:
Get out of bed, beat up and turn your pillow, shake the bedclothes well with at least twenty shakes, then throw the bed open and leave it to cool; in the meanwhile, continuing undressed, walk about your chamber. When you begin to feel the cold air unpleasant, then return to your bed, and you will soon fall asleep, and your sleep will be sweet and pleasant.
Benjamin Disraeli found that he was more comfortable when sleeping in hot weather if he used two beds, moving periodically from the hot, sweaty bed into the cooler one. Benjamin Franklin lit upon the same trick years earlier, but Franklin reckoned he needed four beds to be really cool. William Harvey, the seventeenth-century English physician who discovered the circulation of blood, similarly appreciated that cooling the body helps to induce sleep. According to his contemporary, the biographer John Aubrey, Harvey would tackle his insomnia by cooling himself down until he began to shiver:
He was hot-headed, and his thoughts working would many times keep him from sleeping. He told me that then his way was to rise out of his Bed, and walk about his Chamber in his Shirt, till he was pretty cool, i.e. till he began to have a horror [began to shiver], and then return to bed, and sleep very comfortably.
Another scholar who stumbled across the sleep-inducing properties of cool air was Lord Monboddo, an eccentric eighteenth-century Scottish nobleman and pioneering anthropologist. When Samuel Johnson and James Boswell visited Monboddo, the great sage and his biographer were surprised by their host’s behaviour. As Boswell recorded:
Lord Monboddo told me he awaked every morning at four, and then for his health got up and walked in his room naked, with the window open, which he called taking an air bath; after which he went to bed again, and slept two hours more. Johnson, who was always ready to beat down any thing that seemed to be exhibited with disproportionate importance, thus observed: ‘I suppose, Sir, there is no more in it than this, he awakes at four, and cannot sleep till he chills himself, and makes the warmth of the bed a grateful sensation.’
A less irksome way of achieving a similar effect is to take a hot bath an hour or two before bedtime. The bath will temporarily raise your body temperature. Over the following hours, your temperature will drop again and, all being well, this will help to trigger sleep. Experiments have confirmed that people do feel sleepier at bedtime after taking a hot bath. But the bath must not be too hot, too long or too close to bedtime, or it may have the reverse effect.
The fall in core body temperature that precedes sleep is accompanied by a small rise in the temperature of the hands, feet and other appendages. Blood vessels in your appendages dilate when you lie down to sleep at night, causing them to warm up. As they warm up so your body cools down, helping to send you off to sleep. Experiments have shown that warm feet assist the onset of sleep, bearing out another piece of folk wisdom. One of the best ways of predicting how quickly someone will fall asleep is to measure the temperature gradient across their body. The hands and feet are normally a degree or two cooler than core body temperature, but the temperature difference dwindles to nothing as sleep approaches.
A further demonstration of the linkage between warm appendages and the onset of sleep came from a study of people suffering from a disorder known as vasospastic syndrome. This condition is caused by faults in the physiological mechanisms controlling the peripheral blood vessels, which become less able to dilate. One of the main symptoms is cold hands and feet. As predicted, the cold-toed victims of vasospastic syndrome took longer than normal to fall asleep at night.
The importance of a declining body temperature means that artificial heat sources like electric blankets can disturb sleep. An electric blanket operating between the early hours of the morning and waking will typically increase your core body temperature by about 0.2 degrees Celsius. Even this small increase in body temperature is enough to disrupt sleep.
The sleep-inducing effect of a falling body temperature helps to explain why vigorous physical exercise, which raises body temperature, is not a good idea just before going to bed. It also reminds us why it is inadvisable to eat a large meal shortly before bedtime. The digestive processes that follow a large meal evoke a rise in metabolic rate, which in turn raises body temperature. In an ideal world, a large evening meal would be eaten at least three hours before bedtime. However, this helpful advice is of little use to the many people who work long hours and face long journeys to get home afterwards. They may have barely enough time to prepare and eat an evening meal before going to bed – another example of how lifestyles can conflict with good sleep.
One popular notion that reportedly fails to stand up to scientific scrutiny is that we fall asleep faster after orgasm. A group of enterprising researchers conducted an experiment in which they monitored the sleep of men and women under three different conditions: after the subjects had masturbated to orgasm, after they had masturbated without orgasm, and after they had simply read some nonsexual material. Recordings of their subsequent sleep yielded no evidence that masturbation, with or without orgasm, affected any aspects of sleep, implying that post-coital sleepiness has nothing to do with the attainment of orgasm. (You may find this hard to believe.) This is clearly an area crying out for more research.
The sleep cycle (#ulink_8aefcd07-4655-52e8-bff0-4d696acbd200)
Sleep flooded over him like a dark water.
Jorge Luis Borges, Labyrinths (1964)
Two broadly different states are conventionally bracketed together under the general heading of sleep: rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep. NREM sleep is further subdivided into four different stages, based on their characteristic EEG patterns. Each sleep stage has its own distinctive pattern of brain activity. The various stages and types of sleep alternate cyclically throughout a night’s sleep.
As you become sleepier, your EEG pattern changes. If you are tired enough, this can happen even when you are walking around and supposedly wide awake. The pre-sleep state of quiet restfulness is heralded by the appearance of brain waves of lower frequency and higher voltage, called alpha waves. If you are very sleepy, but still awake, your alpha waves will be accompanied by slow, rolling movements of your eyes. Nearly there. Then you are asleep.
The initial phase of sleep, which has the prosaic name of stage 1, typically lasts only a few minutes. Your muscles start to relax. If you are trying to sleep in a sitting position, the relaxation of your neck muscles will allow your head to slump forward, briefly waking you; your head straightens, you nod off again, and so on. hat is why you ‘nod off’. You can easily be roused into wakefulness from stage 1 sleep. If someone does wake you during stage 1 sleep you may be aware that you have been asleep, or you may be equally convinced that you have been awake the whole time. Stage 1 sleep is accompanied by a further slowing of the brain-wave patterns.
The next phase is known, predictably, as stage 2 sleep. This is signalled by the appearance on the EEG of two specific brain-wave patterns called K complexes and sleep spindles. The K complex is a single, strong wave that lasts less than a second. The sleep spindle is a brief burst of waves lasting less than a second. A sleep spindle on an EEG trace looks like a spindle moving along a loom, hence its name. During stage 2 sleep your eyes are still and your muscles are relaxed. You are less easily awoken by stimuli and you appear to an observer to be sound asleep. Altogether, stage 2 occupies about 45–50 per cent of a night’s sleep.
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Paul Martin
A brilliant overview of that most vital, most underrated and most elusive of human activities, sleep.Using the approach and skills he deployed to such successful effect on the relationship between mind and body in the prize-winning ‘The Sickening Mind’, likeable British popular science author Paul Martin here tackles the science of that most mysterious, elusive and alluring of human activities, sleeping, and draws on both cutting-edge neuroscience and classic literature to do so.We spend one third of our lives asleep, but know hardly anything about it, and can remember so little of it as we come out of it. Why?Are dreams the place we go to resolve our problems, emasculate our fears and rehearse our hopes? Why are we paralysed when we dream? Why did sleep evolve?And is anybody getting enough sleep?
COUNTING SHEEP
The Science and Pleasures of Sleep and Dreams
PAUL MARTIN
Copyright (#ulink_3520a952-75a8-598d-ac67-5a97b134707f)
William Collins
An imprint of HarperCollinsPublishers 1 London Bridge Street London SE1 9GF
www.harpercollins.co.uk (http://www.harpercollins.co.uk/)
Published by HarperPress 2003
First published in Great Britain by HarperCollinsPublishers 2002
Copyright © Paul Martin 2002
Paul Martin asserts the moral right to be identified as the author of this work
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Source ISBN: 9780006551720
Ebook Edition © MARCH 2016 ISBN: 9780007406784
Version: 2016-02-11
Contents
Cover (#ua80fc455-2f27-5d7c-9fca-eb9476ae9cb0)
Title Page (#u9107714d-ed60-510f-8976-9b68940ee021)
Copyright (#u8bab2137-8c70-51b4-aad3-c41332c36563)
PART I: PRELIMINARIES (#u534b858d-4b59-5aa3-ab51-070d7768eea6)
1: A Third of Life (#uc050b292-b7ef-520d-9723-b15099ecb4b3)
A sleep-sick society? (#ulink_e2384876-eacb-5ddd-8084-65fbf35183ed)
The universal imperative (#ulink_ed620ba9-9745-5479-9f07-85a8ec6715f3)
Half asleep (#ulink_08143b2d-cd18-50f8-ad75-388778404476)
Nice, not naughty (#ulink_c0444367-682c-53a6-89e9-a12457fba012)
PART II: INSUFFICIENCIES (#ub710fa96-b025-54af-bf3b-5b7d70b3a5a7)
2: Sleepy People (#u85dea0be-480b-570b-aad0-925a575e8049)
Are we sleep-deprived? (#ulink_fe5a0cad-4d97-5b63-a7bb-d9cf7daea491)
Are you sleep-deprived? (#ulink_4147fc1b-77dd-5d2f-9ba6-ab5571ad6dd1)
Reasons for not sleeping (#ulink_d08c104c-673c-54bf-87e4-56c1369891c4)
Ancient and modern (#ulink_e73b743e-63df-5856-a4d6-90093cd1dd70)
Sleepy drivers (#ulink_0643902d-ddb4-5187-8819-0cd9e711ee35)
Sleepy pilots (#ulink_838729e3-6261-5c3b-9997-d00f25214ee1)
Sleepy doctors (#ulink_36b6e00e-5b16-5e6f-9770-a2d0c6b82975)
The madness of politicians (#ulink_6cc25b44-5507-554b-aca7-673fc0d8e902)
Truly, madly, sleepily (#ulink_9d6ee05c-2417-52dd-8ea8-2302adb003cf)
The price of eternal vigilance is liberty (#ulink_69da4085-2e99-5364-b785-5c1b1f2d4f65)
3: Dead Tired (#u30b7ddb6-7431-5612-b355-a029da480b32)
Sleepiness (#ulink_81fa281f-3984-51f4-b95c-dedd4680d9fe)
Fighting the beast (#ulink_46a4edee-a805-5e7f-8889-4f3c6107acdb)
A soil for peevishness (#ulink_35a0e7d1-d74a-5bfe-a66b-b06123da7134)
Tired people are stupid and reckless (#ulink_ef3870d3-3db6-5d18-b4b7-60db998cfccc)
Alcohol, beauty and old age (#ulink_a02e9f05-03d5-5079-b204-3bf3edf53a1d)
Champion wakers (#ulink_75db5262-c5f6-5a34-878a-5723c74b53a2)
Uses and abuses (#ulink_1d3af885-9d46-5d54-ae0b-38ea58ba6325)
4: The Golden Chain (#uffe99068-ecfa-5859-a988-74273041693f)
A waking death (#ulink_6754d5e1-dc33-521d-b290-ac9245933eaf)
Body and soul (#ulink_4dda6a11-388e-5383-bff7-d610f33294aa)
Sleep, immunity and health (#ulink_f4684fd9-9e90-50a3-9042-3bedd31d071d)
The Battle of Stalingrad (#ulink_447371da-4d9c-5f24-ac9a-04c82ed1406c)
Sleepless in hospital (#ulink_706213d3-ec7d-53b4-80e6-565c0cf5b4e3)
PART III: MECHANISMS (#uac3c47f7-b4f2-5ea4-9c81-15fc01e5a6e9)
5: The Shapes of Sleep (#u39a528ce-bde6-5898-a17d-f15c306aec06)
Measuring sleep (#ulink_d9d736a1-548b-542b-9ac6-6d7ca5da5a06)
Falling asleep again, what am I to do? (#ulink_6b3ede10-1c7a-5e9b-8fe7-0cedc375b51f)
The sleep cycle (#ulink_82872f29-2e72-5581-8be5-eabbd536e4ab)
The paradoxical world of REM (#litres_trial_promo)
The sleep cycle continued (#litres_trial_promo)
Waking up (#litres_trial_promo)
The quality of sleep (#litres_trial_promo)
Meditating – or only sleeping? (#litres_trial_promo)
6: Morpheus Undressed (#litres_trial_promo)
The rhythms of life (#litres_trial_promo)
So SAD (#litres_trial_promo)
Larks and owls (#litres_trial_promo)
Genes and sleep (#litres_trial_promo)
A sleeplessness that kills (#litres_trial_promo)
7: Strange Tales of Erections and Yawning (#litres_trial_promo)
Nocturnal erections (#litres_trial_promo)
The mystery of yawning (#litres_trial_promo)
8: Friends and Enemies of Sleep (#litres_trial_promo)
Brother caffeine (#litres_trial_promo)
Sister alcohol (#litres_trial_promo)
Tobacco (#litres_trial_promo)
Food for sleep (#litres_trial_promo)
Exercise is bunk, isn’t it? (#litres_trial_promo)
Things that go bump in the night (#litres_trial_promo)
Shift work (#litres_trial_promo)
Poppy, mandragora and drowsy syrups (#litres_trial_promo)
Hypnotic exotica (#litres_trial_promo)
PART IV: DREAMS (#litres_trial_promo)
9: The Children of an Idle Brain? (#litres_trial_promo)
To sleep, perchance … (#litres_trial_promo)
Do flies dream? (#litres_trial_promo)
A dream within a dream? (#litres_trial_promo)
Dreaming as madness (#litres_trial_promo)
Are dreams meaningful? (#litres_trial_promo)
Like wine through water (#litres_trial_promo)
Can dreams be sinful? (#litres_trial_promo)
10: A Second Life (#litres_trial_promo)
A creative state (#litres_trial_promo)
Stevenson’s Brownies (#litres_trial_promo)
Lucid dreams (#litres_trial_promo)
The great dreamer (#litres_trial_promo)
PART V: ORIGINS (#litres_trial_promo)
11: From Egg to Grave (#litres_trial_promo)
Screaming babies (#litres_trial_promo)
Bad children (#litres_trial_promo)
Yawning youth (#litres_trial_promo)
Old and grey and full of sleep (#litres_trial_promo)
12: The Reason of Sleep (#litres_trial_promo)
The evolution of sleep (#litres_trial_promo)
What is sleep for? (#litres_trial_promo)
What is REM sleep for? (#litres_trial_promo)
Reverse learning (#litres_trial_promo)
To sleep, perchance to learn (#litres_trial_promo)
Should machines sleep? (#litres_trial_promo)
PART VI: PROBLEMS (#litres_trial_promo)
13: Bad Sleepers (#litres_trial_promo)
An intolerable lucidity (#litres_trial_promo)
Why can’t you sleep? (#litres_trial_promo)
Storm and stress and sleep (#litres_trial_promo)
What to do? (#litres_trial_promo)
Staying awake (#litres_trial_promo)
14: Dark Night (#litres_trial_promo)
Walking and talking (#litres_trial_promo)
Nightmares, night terrors, sleep paralysis and the Old Hag (#litres_trial_promo)
Moving sleep (#litres_trial_promo)
Midnight feasting (#litres_trial_promo)
Soggy sheets (#litres_trial_promo)
Aching heads (#litres_trial_promo)
Troubled guts (#litres_trial_promo)
Troubled minds (#litres_trial_promo)
Sudden nocturnal death (#litres_trial_promo)
Narcolepsy (#litres_trial_promo)
15: Pickwickian Problems (#litres_trial_promo)
The wonderful world of snoring (#litres_trial_promo)
Silence is golden (#litres_trial_promo)
Breathless in bed (#litres_trial_promo)
Consequences – mostly dire (#litres_trial_promo)
Unblocking those tubes (#litres_trial_promo)
PART VII: PLEASURES (#litres_trial_promo)
16: And So to Bed (#litres_trial_promo)
A brief history of beds (#litres_trial_promo)
Sleeping partners (#litres_trial_promo)
17: An Excellent Thing (#litres_trial_promo)
Puritans and hypocrites (#litres_trial_promo)
Naps, nappers and napping (#litres_trial_promo)
Sweet dreams (#litres_trial_promo)
Blessed oblivion (#litres_trial_promo)
Give sleep a chance (#litres_trial_promo)
In praise of horizontalism (#litres_trial_promo)
Keep Reading (#litres_trial_promo)
References (#litres_trial_promo)
Index (#litres_trial_promo)
Acknowledgements (#litres_trial_promo)
About the Author (#litres_trial_promo)
Praise (#litres_trial_promo)
Also by the Author (#litres_trial_promo)
About the Publisher (#litres_trial_promo)
PART I Preliminaries (#ulink_d19660b1-89c0-5a86-8526-91b26e8f214f)
1 A Third of Life (#ulink_31cf6e27-a8e6-5a49-86cd-f1af9fe822b4)
Man … consumes more than one third of his life in this his irrational situation.
Erasmus Darwin, Zoonomia (1801)
Sleep: a state so familiar yet so strange. It is the single most common form of human behaviour and you will spend a third of your life doing it – 25 years or more, all being well. When you die, a bigger slice of your existence will have passed in that state than in making love, raising children, eating, playing games, listening to music, or any of those other activities that humanity values so highly.
Sleep is a form of behaviour, just as eating or socialising or fighting or copulating are forms of behaviour, even if it is not the most gripping to observe. Most of the action goes on inside the brain. It is also a uniquely private experience, even when sharing a bed. When we are awake we all inhabit a common world, but when we sleep each of us occupies a world of our own. Most of us, however, have precious little awareness of what we experience in that state. Our memories of sleeping and dreaming mostly evaporate when we awake, erasing the record every morning.
Many of us do not get enough sleep and we suffer the consequences, often without realising what we are doing to ourselves. The demands of the 24-hour society are marginalising sleep, yet it is not an optional activity. Nature imposes it upon us. We can survive for longer without food. When our sleep falls short in quantity or quality we pay a heavy price in depressed mood, impaired performance, damaged social relationships and poorer health. But we usually blame something else.
Sleep is an active state, generated within the brain, not a mere absence of consciousness. You are physiologically capable of sleeping with your eyelids held open by sticking plaster, bright lights flashing in your eyes and loud music playing in your ears. We shall later see how science has revealed the ferment of electrical and chemical activity that goes on inside the brain during sleep, and how the sleeping brain operates in a quite different mode from waking consciousness. We shall see too how lack of sleep erodes our quality of life and performance while simultaneously making us more vulnerable to injuries and illness. Science amply supports William Shakespeare’s view that sleep is the ‘chief nourisher in life’s feast’.
What is sleep and what is it for? Why do so many people have such problems with it? Why do we dream? Although sleep forms a central strand of human and animal life it is still poorly understood and widely neglected. It is an inglorious example of familiarity breeding contempt. Sleep is so much a part of our everyday existence that we take it for granted. We are ignorant even of our ignorance. In 1758, Doctor Samuel Johnson summed it up like this:
Among the innumerable mortifications that waylay human arrogance on every side may well be reckoned our ignorance of the most common objects and effects … Vulgar and inactive minds confound familiarity with knowledge, and conceive themselves informed of the whole nature of things when they are shown their form or told their use … Sleep is a state in which a great part of every life is passed. No animal has been yet discovered whose existence is not varied with intervals of insensibility. Yet of this change so frequent, so great, so general, and so necessary, no searcher has yet found either the efficient or final cause; or can tell by what power the mind and body are thus chained down in irresistible stupefaction; or what benefits the animal receives from this alternate suspension of its active powers.
The scientists who do know something about sleep often bemoan society’s ignorance of it. They point to the vast gap between current scientific understanding of sleep, patchy though it is, and the practical benefits it could bring if that knowledge were absorbed and acted upon by society. Our collective indifference towards sleep has enormous and largely avoidable costs.
A sleep-sick society? (#ulink_2011d958-bc4c-5573-9ede-d62f2c781ff1)
The mere presence of an alarm clock implies sleep deprivation, and what bedroom lacks an alarm clock?
James Gleick, Faster (1999)
All is not well with the state of sleep. Many of us depend on an alarm clock to prise us out of bed each morning, and children’s bedrooms increasingly resemble places of entertainment rather than places of sleep. When given the opportunity, we sleep in at the weekends and feel only half awake when we do get up. On that long-awaited holiday we find the change of scenery (or is it the air?) makes us even sleepier. We are told that lying around and sleeping too much will only make us sleepier. But in truth we feel sleepy at weekends and on holidays not because we are sleeping too much, but because we have slept too little the rest of the time.
A century ago the majority toiled long hours while the affluent few idled away their time. Today, however, the more conventionally successful you are, the less free time you will probably have. Having nothing to do is seen as a sign of worthlessness, while ceaseless activity signifies status and success. Supposedly unproductive activities are deprioritised or delegated. And according to prevailing cultural attitudes, sleeping is one of the least productive of all human activities – more worthwhile perhaps than sitting around picking your nose, but not much. In their ceaseless pursuit of work and pleasure the cash-rich buy time from others, hiring them to clean their houses, look after their children and cook their food. But one of the activities you simply cannot delegate to anyone else is sleeping.
Evolution equipped humans, in common with all other animals, with biological mechanisms to make us sleep at roughly the same time every day. However, those mechanisms evolved to cope with a pre-industrial world that was vastly different from the one we now inhabit.
Our daily cycles of sleep and activity are no longer driven by dawn and dusk, but by clocks, electric lighting and work schedules. Sleep has become increasingly devalued in the 24-hour society. Many regard sleep as wasted time and would prefer to sacrifice less of their busy lives to it. We live in a world where there are too many tired, sleep-deprived people. Think of those pinched, yawning faces you can see every day on the trains and in buses and in cars crawling through jams. They look as if they have been brainwashed, but they are just tired.
We pay a steep price for neglecting sleep, in our ignorance and indifference. The scientific evidence tells us that far too many people in industrialised societies are chronically sleep-deprived, with damaging consequences for their mental and physical health, performance at work, quality of life and personal relationships. William Dement, a pioneering scientist in the field, believes that we now live in a ‘sleep-sick society’. Scientists have not yet reached a consensus about the precise extent of sleep deprivation in society, but they do all agree that sleepiness is a major cause of accidents and injuries. In fact, sleepiness is responsible for far more deaths on the roads than alcohol or drugs.
Everyone has heard about the need for a balanced diet and physical exercise, even if many of us fail to follow the advice. But sleep is lost in a deep well of ignorance and apathy. Even the medical profession pays it scant regard. Sleep and its disorders barely feature in the teaching of medicine, and few physicians are fully equipped to deal with the sleep problems they regularly encounter. When researchers from Oxford University investigated British medical education in the late 1990s, they discovered that the average amount of time devoted to sleep and sleep disorders in undergraduate teaching was five minutes, rising to a princely peak of 15 minutes in preclinical training. Your doctor is therefore unlikely to be an expert on the subject.
The general public and the medical profession are not the only ones to display a remarkable indifference to sleep. So too do most contemporary writers. Considering that sleep accounts for a third of human existence, it features remarkably rarely in novels, biographies, social histories or learned texts on neurobiology, psychology and medicine. And the few accounts that have made it into print are mostly concerned with what happens when it goes wrong. Insomnia and nightmares loom large in the tiny literature of sleep.
Few biographies mention the sleep behaviour or dreams of their subjects. That part of their story is almost invariably missing, as if somehow we all cease to exist at night. And most of those scholarly books that set out to explain how the human mind works say little or nothing about what goes on during the several hours of every day when the mind is sleeping and dreaming. They are really just books about how the brain works when it is awake. Our neglect of sleep is underlined by its absence from our literature.
Vladimir Nabokov once said that all the great writers have good eyes. What has happened to the eyes of writers as far as sleep and dreams are concerned? It was not always so. Older literature is distinctly richer in references to sleeping and dreaming, perhaps because darkness and sleep and dreams were much more prominent aspects of everyday life before the invention of the electric light bulb and the advent of the 24-hour society. Shakespeare’s works are thick with allusions to sleep and dreams, as are Dickens’s. We shall encounter some of them later. Meanwhile, to set the right tone, here is Sancho Panza’s eulogy to sleep from Don Quixote:
God bless the inventor of sleep, the cloak that covers all man’s thoughts, the food that cures all hunger, the water that quenches all thirst, the fire that warms the cold, the cold that cools the heat; the common coin, in short, that can purchase all things, the balancing weight that levels the shepherd with the king and the simple with the wise.
The universal imperative (#ulink_3acf04c4-0b0c-541e-974a-051f57e446a0)
Almost all other animals are observed to partake of sleep, aquatic, winged, and terrestrial creatures alike. For every kind of fish and the soft-shelled species have been seen sleeping, as has every other creature that has eyes.
Aristotle (384–322 BC), On Sleep and Waking
Sleep is a universal human characteristic, like eating and drinking. Absolutely everybody does it. Sleep occupies about one third of each human life, and up to two thirds of a baby’s time. (According to Groucho Marx, the proportion rises to three thirds if you live in Peoria.) It is a common bond that ties us all together. We have no choice: the longer we go without sleep, the stronger our desire for it grows. Tiredness, like hunger and thirst, will eventually force us to do the right thing whether we want to or not.
The dreams that accompany sleep are equally ubiquitous features of human life, even if many of us retain little memory of them after we awake. Dreaming is a classless activity that unites monarchs and paupers, a thought that Charles Dickens mused upon in one of his essays:
Here, for example, is her Majesty Queen Victoria in her palace, this present blessed night, and here is Winking Charley, a sturdy vagrant, in one of her Majesty’s jails … It is probable that we have all three committed murders and hidden bodies. It is pretty certain that we have all desperately wanted to cry out, and have had no voice; that we have all gone to the play and not been able to get in; that we have all dreamed much more of our youth than of our later lives.
Sleep is not a specifically human trait, of course. On the contrary, it is a universal characteristic of complex living organisms, as Aristotle deduced more than 23 centuries ago. Sleep is observed in animals of every sort, including insects, molluscs, fish, amphibians, birds and mammals. Within the animal world, sleep does vary enormously in quantity, quality and timing, accounting for anything up to 80 per cent of some animals’ lifespans. But they all do it, one way or another. Some species, especially predators, spend more of their lives asleep than they do awake, a fact that TV documentaries and natural-history books seldom mention.
How do we know that an animal is sleeping? It is hard enough sometimes to be sure that a human is asleep, let alone a fish or a fly. The ultimate indicator of whether an animal or person is asleep is the distinctive pattern of electrical activity in its brain. During deep sleep the billions of individual nerve cells in the brain synchronise their electrical activity to some extent, generating characteristic waves of tiny voltage changes that can be detected by electrodes placed on the scalp. We shall be exploring the nature and internal structure of sleep later. The easiest way to recognise sleep, however, is from overt behaviour.
Sleep has several rather obvious distinguishing characteristics. A sleeping person or animal will generally remain in the same place for a prolonged period, perhaps several hours. There will be a certain amount of twitching, shifting of posture and fidgeting. Young animals will suckle while they sleep and ruminants will carry on chewing the cud. But sleepers normally do not get up and change their location. (When they do, we recognise it as a curious phenomenon and call it sleepwalking.)
Sleeping organisms also adopt a characteristic posture. Sloths and bats, for example, sleep hanging upside down from a branch. The Mediterranean flour moth sleeps with its antennae swivelled backwards and the tips tucked under its wings. If you are careful, you can gently lift the sleeping moth’s wing without disturbing it – a trick that will definitely not work when it is awake. A lizard will settle on a branch during the hours before sunset, curl up its tail, close its eyelids, retract its eyeballs and remain in that distinctly sleep-like posture all night unless it is disturbed. A partridge, like many birds, will rest its weight on one leg while it sleeps. It is said that some gourmets can tell which leg, from its taste.
Monkeys and apes, including humans, usually sleep lying down. Indeed, we are built in such a way that we find it difficult to sleep properly unless we are lying down. People can and sometimes do sleep after a fashion while sitting, notably in aeroplanes, business meetings and school classrooms. If you are really exhausted, you might even manage to snatch some sleep standing up. But sleep taken while standing or sitting upright is generally fitful, shallow and unrefreshing. The non-horizontal sleeper may repeatedly nod off, but as soon as they descend beyond the shallowest stages of sleep their muscles relax, they begin to sway and their brain wakes them up again. That is why we ‘nod off’. If you travel frequently on trains or buses, you might have had the dubious pleasure of sitting next to a weary commuter who has nodded off all over your shoulder. Recordings of brain-wave patterns show that people sleeping in an upright sitting position achieve only the initial stages of light sleep, not the sustained, deep sleep we require to wake up feeling truly refreshed. The reason is simple. Our muscles relax when we are fully asleep and we would fall over if we were not already lying down. Our brains therefore do not permit us to enter sustained, deep sleep unless we are in a physically stable, horizontal (or near-horizontal) posture.
Despite the virtual impossibility of sleeping deeply while sitting upright, we are sometimes forced to try. In Down and Out in Paris and London, George Orwell describes a particularly unwelcoming form of overnight accommodation that was known to the homeless of prewar London as the Twopenny Hangover. At the Twopenny Hangover the night’s residents would sit in a row along a bench. In front of them was a rope, and the would-be sleepers would lean on this rope as though leaning over a fence. In that posture they were supposed to sleep. At five o’clock the next morning an official, wittily known as the valet, would cut the rope so that the residents could begin another day of wandering the streets.
Nowadays, tourist-class airline passengers travelling long distances can enjoy an experience similar to the Twopenny Hangover, albeit at vastly greater expense. George Orwell’s autobiographical account of grinding poverty in the late 1920s is also a sharp reminder that lack of money is often accompanied by lack of decent sleep. Rough sleepers rarely get a good night’s sleep.
Sleep has several other distinctive characteristics besides immobility and posture. In many species, including humans, individuals return to the same place each night (or each day, if they are nocturnal) in order to sleep. More generally, all members of a given species will tend to choose the same sorts of sleeping places. The distinctive feature of those places is often their security. Birds usually sleep on inaccessible branches or ledges. Many small mammals sleep in underground burrows where they are safer from predators. Fishes lie on the bottom, or wedge themselves into a crevice or against the underside of a rock. We humans prefer to sleep in relatively private and secure places. Given the choice, we rarely opt to sleep on busy streets or in crowded restaurants.
One obvious feature of sleep is a marked reduction in responsiveness to sights, sounds and other sensory stimuli. To provoke a response from a sleeping organism, stimuli have to be more intense or more relevant to the individual. For example, the reef fish known as the slippery dick sleeps during the hours of darkness, partly buried in the sand. While it is in this state, the sleeping slippery dick can be gently lifted to the surface by hand without it waking up and swimming off.
A sort of perceptual wall is erected during sleep, insulating the mind from the outside world. You would still be able to sleep if you had no eyelids, because your sleeping brain would not register what your eyes could see. This sensory isolation is highly selective, however. You can sleep through relatively loud noises from traffic or a radio, but a quiet mention of your name can rouse you immediately. Your brain is not simply blocked off during sleep. Moreover, this reduced responsiveness is rapidly reversible – a characteristic that distinguishes sleep from states such as unconsciousness, coma, anaesthesia and hibernation. A suitable stimulus, particularly one signifying immediate danger, can snap a sleeping person into staring-eyed alertness in an instant.
Another diagnostic feature of sleep is its regular cycle of waxing and waning. Living organisms sleep and wake according to a regular 24-hour cycle, or circadian rhythm. All members of a given species tend to sleep during the same part of the 24-hour cycle, when their environment is least favourable for other activities such as looking for food. For most species this means sleeping during the hours of darkness, but some species do the reverse. Many small mammals, which would be more vulnerable to predators during daylight, sleep by day and forage at night. Aside from a few nocturnal specialists such as owls, birds cannot easily fly in the dark, and most reptiles find it hard to maintain a sufficiently high body temperature to be active during the cool of night. Most birds and reptiles therefore sleep at night. Predators tend to sleep when their prey are asleep and hunt when their prey are up and about.
Sleep, then, is characterised by a special sleeping place and posture, prolonged immobility, a selective and rapidly reversible reduction in responsiveness to stimuli, and a 24-hour cycle. According to these and other criteria, all mammals, birds, fish, amphibians, reptiles and insects that have been inspected have been found to sleep.
Take the humble fruit fly, Drosophila melanogaster, for example. This small insect displays all the key features of sleep, and more. Fruit flies alternate between periods of activity and rest according to a 24-hour cycle. They go to sleep in a preferred location where they remain immobile for two hours or more at a time, usually at around the same time of day. While they are asleep, they are much less reactive to sights, sounds and other sensory stimuli. If they are prevented from sleeping they show an increasing propensity to sleep. And when they do sleep after a period of deprivation, they are harder to wake up and they sleep for longer, as if catching up. Young fruit flies sleep more than old fruit flies, just as babies sleep more than adult humans. And, also like humans, their sleep is assisted by sleep-inducing drugs and disrupted by stimulants such as caffeine.
Many small mammals spend more than half their lives asleep. Think of the dormouse, for example. Lewis Carroll’s description in Alice’s Adventures in Wonderland is biologically authentic, apart from the animals’ ability to talk grammatical English:
There was a table set out under a tree in front of the house, and the March Hare and the Hatter were having tea at it: a Dormouse was sitting between them, fast asleep, and the other two were resting their elbows on it, and talking over its head. ‘Very uncomfortable for the Dormouse,’ thought Alice; ‘only, as it’s asleep, I suppose it doesn’t mind’…
‘You might just as well say that “I see what I eat” is the same thing as “I eat what I see”!’
‘You might just as well say,’ added the March Hare, that “I like what I get” is the same thing as “I get what I like”!’
‘You might just as well say,’ added the Dormouse, who seemed to be talking in his sleep, ‘that “I breathe when I sleep” is the same thing as “I sleep when I breathe”!’
‘It is the same thing with you,’ said the Hatter.
Dormice (which actually comprise 20 different species of nocturnal rodents) really do spend most of their time asleep, as do many other species of small mammals. The volcano mouse spends more than 17 hours a day asleep. Even the naked mole rat devotes 12 hours a day to sleep, despite the fact that it lives underground and has become so adapted to subterranean life that it has lost the power of sight.
The champion sleepers are two-toed sloths, which dedicate an average of 20 hours a day, or more than 80 per cent of their entire lives, to sleep. (Whereas three-toed sloths are much livelier, sleeping for a mere 17 hours a day.) Close behind come armadillos, opossums and some species of bats, which sleep for 18–19 hours a day. Many lizards spend more than 16 hours a day in sleep. Nearer to home, cats, rats, mice and hamsters sleep for 13–14 hours a day. Birds too can be great sleepers, although their sleep is less obvious to the casual observer because it is fragmented into short episodes. Starlings, which are fairly typical, spend a total of more than nine hours a day asleep, but this is split into many short bouts, each lasting on average only seven minutes. At the other end of the sleep spectrum lurk the wakeful grazers – cows, goats, elephants, donkeys, horses, sheep, deer and giraffes – all surviving on a meagre ration of three or four hours a day. But that is the minimum.
We humans occupy the low-to-middle ground of the zoological sleep spectrum, along with moles – or, at least, we do if we assign ourselves the proverbial eight hours a night. In reality, most people get substantially less than eight hours – a theme we shall be exploring in the next three chapters. On that same theme, it is notable that our closest biological relatives, the apes and monkeys, sleep more than us. Chimpanzees, rhesus monkeys, squirrel monkeys, vervets, patas monkeys and baboons sleep nine or ten hours a night, while the gorilla averages 12 hours. The sleepiest primate is the owl monkey, which clocks up 17 hours a day of sleep, accounting for more than 70 per cent of its life.
Do plants sleep? This is almost, but not quite, as stupid a question as it may seem. In one loose and misleading sense plants do display some behavioural characteristics of sleep. Many plants alter their shape each night, as though curling up to go to sleep. Some species furl their leaves like an umbrella, some allow their leaves to droop as if they need watering, while others, including lettuces and radishes, point their leaves vertically upwards. They all display a distinct 24-hour circadian rhythm.
Pliny the Elder noted this ‘sleep of plants’ in the first century AD. Eighteen centuries later, Charles Darwin investigated the ‘sleep of plants’ with a series of ingenious experiments in the garden of his home at Down House in Kent. Darwin was confident that the phenomenon was not true sleep. ‘Hardly any one,’ he wrote, ‘supposes that there is really any analogy between the sleep of animals and that of plants.’ As usual, Darwin was right. His experiments demonstrated that plants alter their shape at night to protect themselves from their physical environment. He found, for example, that if he left a plant outside at night, with its leaves tied up to prevent them from drooping, the result was a blackened, shrivelled and dead plant the next morning. Darwin also discovered that a plant will not ‘sleep’ if it is shaken violently.
Half asleep (#ulink_f6c0db3f-e53f-5b4f-8023-863d7fec0ad1)
And the small fowl are making melody
That sleep away the night with open eye
Geoffrey Chaucer, Prologue to The Canterbury Tales (c. 1387)
Sleep is such an overriding biological imperative that evolution has found ingenious ways of enabling animals to do it in the face of formidable obstacles. Nature, it seems, will do almost anything to ensure that animals sleep.
Consider dolphins, for example. They are air-breathing mammals like us, so they must swim to the surface each time they want to take a breath. They would drown if they fell into deep sleep while deep underwater. One possible solution to this biological design conundrum would be to wake up each time a breath of air was required. However, evolution has produced a more elegant solution: only one half of the dolphin’s brain goes to sleep at a time.
Dolphins are capable of what is known as unihemispheric sleep, in which one hemisphere of the brain submerges into deep sleep while the other hemisphere remains awake. The two halves of the brain take it in turns to sleep, swapping at intervals of between one and three hours. This cerebral juggling trick enables dolphins to sleep underwater without drowning, which is just as well considering that they spend a good third of their lives asleep. Unihemispheric sleep has been recorded in several species of dolphins, porpoises and whales, including bottlenosed and Amazonian dolphins, Black Sea porpoises and white whales.
Despite the apparent convenience of being able to sleep and stay awake simultaneously, very few mammals are capable of unihemispheric sleep. The biological benefits of sleeping with only half of the brain at a time presumably outweigh the disadvantages only under unusual conditions, such as those encountered by air-breathing mammals living in the deep oceans.
Unihemispheric sleep is widespread in birds, however. They do it for a. different biological reason. Sleeping with half the brain awake and one eye open allows them to sleep while simultaneously remaining vigilant for predators. In birds, each eye exclusively feeds the visual processing areas in the opposite half of the brain: thus, all the nerve fibres coming from the right eye connect to the left hemisphere of the brain and vice versa. When a bird is in unihemispheric sleep its open eye is the one corresponding to the waking half of the brain, while the closed eye is connected to the sleeping half. If a bird feels relatively safe, it closes both eyes, and both sides of its brain go to sleep.
An experiment with mallard ducks demonstrated how unihemispheric sleep helps birds to stay safe from predators. Four ducks were placed in a row along a perch, the idea being that the ducks at either end of the row would feel more vulnerable to predators than the two in the middle. In the natural world it is generally a bad idea to be on the edge of a group if you might end up as some other animal’s dinner. As predicted, video recordings showed that the outer two birds were much more likely to sleep with one eye open than the two on the inside; their unihemispheric sleep increased by 150 per cent. The amount of unihemispheric sleep rose further when the ducks were shown frightening video images of an approaching predator.
The relationship between unihemispheric sleep and vigilance was finely controlled. The exposed birds on the ends of the row preferentially opened their outward-facing eye – the one directed towards potential danger. From time to time, a bird would turn round and switch eyes, so that the open eye was still the one facing out. Simultaneous recordings of brain activity confirmed that the brain hemisphere corresponding to the open eye was always awake, while the hemisphere corresponding to the closed eye was the one in deep sleep.
The one-eyed tactic was effective: when an attacking predator was simulated on a video screen, the birds sleeping with one eye open were able to react in a fraction of a second – far faster than if they had been in deep sleep with both eyes shut.
Humans are not capable of unihemispheric sleep, although at least one writer has played with the fantasy. Damon Runyon wrote of how he once played cards with a fading champion card player who now lacked the stamina to stay awake during marathon games of gin rummy lasting eight or ten hours. When the man lost a game after making a bad play, the punters betting on him to win clamoured to remove their bets from the next game, on the grounds that he was asleep. Then someone pointed out that the allegedly sleeping player’s eyes were open, so he must be awake. ‘The one on your side is’, retorted one of the backers, ‘but the one on the other side is closed. He is sleeping one-eye.’
Nice, not naughty (#ulink_f454c206-f464-5b51-a885-99cef8a7c075)
Like all other forms of pleasure, sleep may become a passion.
Jean-Anthelme Brillat-Savarin, The Physiology of Taste (1825)
Sleep is far more than just a biological necessity. It is also a neglected source of pleasure. Consider this. Activities that are biologically important for survival and reproduction tend to be enjoyable: think of sex, or eating, or drinking, or being successful. Pleasure is one of nature’s ways of ensuring that animals do enough of the right things. Whatever happened to sleep? It is clearly essential for survival, and yet for many people it is merely a maintenance activity that brings little positive enjoyment. They sleep because they have to rather than because they want to.
In some respects, sleep has acquired the dismal status that eating had in post-war Britain, where austerity and a cultural blind spot reduced the culinary arts to a joyless act of refuelling. Bland, fatty food was daily shovelled in to keep the boilers stoked, with scant attention paid to its preparation or enjoyment. Fortunately, Britain has since developed more enlightened (if not self-indulgent) attitudes to food, and recent decades have witnessed cooking and eating emerge as pleasurable activities in their own right. For some people in wealthy nations, cooking and eating have become more a form of entertainment than a biological function.
Meanwhile, sleep is mired in the cultural equivalent of a 1950s British canteen meal: an inadequate and faintly unhealthy affair, indifferently concocted and consumed with more haste than enjoyment. Too many people regard sleep as the brain’s equivalent of fast food or overboiled cabbage. If gastronomy is ‘the reasoned comprehension of everything connected with the nourishment of man’, as it was originally defined, then should we not start thinking about sleep in the same way? I hope that by the end of this book you will be pondering the gourmet delights of sleeping, napping and dreaming, and starting to savour more of their lost pleasures for yourself.
PART II Insufficiencies (#ulink_330b3f66-5320-565b-852f-411cb70abccd)
2 Sleepy People (#ulink_e05442f8-5755-5aba-af92-a246577561ed)
She looked a little worn out, a little tired, but, then again, didn’t everybody? We all look a bit tired, these days, some more than others.
William Boyd, Armadillo (1998)
Many of us in our everyday lives are getting sleep of inadequate quantity and quality, and this is bad for our mental and physical health. Lack of sleep makes us inefficient at work, dangerous behind the wheel of a car and unattractive to be with; it lowers the quality of our lives, causes accidents and makes us more vulnerable to illness. And it is unpleasant.
I am not referring here to the acute sleep deprivation that comes from occasionally staying up all night, although that is common enough in professions such as medicine, the military and politics. Rather, I am talking about the chronic sleep deprivation that accumulates as we continually stint ourselves of sleep, day in and day out, because of the conflicting demands of work and leisure, or because of a sleep disorder, or just because we do not think sleep is important. So, what are the reasons for believing that sleep deprivation is a real problem?
Are we sleep-deprived? (#ulink_d2dc7e05-d856-5dd1-a091-37a92322eef6)
Eight hours they give to sleep.
Sir Thomas More, Utopia (1551)
The evidence that chronic sleep deprivation is a common feature of contemporary life comes in several interlinked strands. We will start with perhaps the most obvious one of all: the observation that many people feel sleepy when they are awake.
Assessing the extent of daytime tiredness in society is tricky, not least because so many people have come to regard feeling tired as normal. Nonetheless, numerous scientific studies have unearthed evidence that the problem is real and widespread. For example, a 2001 poll of Americans’ sleeping habits found that 22 per cent of adults felt so sleepy during the day that it interfered with their activities. A 1994 survey found that 5 per cent of the British population were experiencing severe daytime sleepiness, while a further 15 per cent felt moderately sleepy during the day. It also found that the people suffering from daytime sleepiness were twice as likely to have a vehicle accident.
A similar picture has emerged from other countries. For instance, a recent study discovered that 10 per cent of middle-aged Finns were excessively tired and tended to fall asleep unintentionally during the day. Their sleepiness was statistically associated with an array of nasty things, including a heightened risk of traffic accidents, premature retirement, depression and anxiety. In Sweden, 9 per cent of adults were found to be suffering from daytime sleepiness, while a survey in Warsaw recorded that 21 per cent of adults felt moderately sleepy during the day. Australian researchers detected excessive daytime sleepiness in 11 per cent of adults. You get the picture. Not even the youngest and healthiest are immune. A French investigation of 58,000 army conscripts discovered that 5 per cent of these fit young men were affected by excessive daytime sleepiness and 14 per cent of them were sufficiently tired to sleep during the day.
Overall, it is safe to conclude that at least one in ten adults in the general population (you, me and the people next door) are currently affected by moderate or severe daytime sleepiness. Some scientists believe the situation is much worse, with up to one in three adults suffering from significant sleepiness. A major review undertaken by the US National Commission on Sleep Disorders Research estimated that as many as 70 million Americans – more than a quarter of the population – were suffering from sleep deprivation or some form of sleep problem, at a direct cost to the national health care bill of about 16 billion dollars a year. The Commission’s report concluded that:
A convincing body of scientific evidence and witness testimony indicates that many Americans are severely sleep-deprived and, therefore, dangerously sleepy during the day … By any measuring stick, the deaths, illness, and damage due to sleep deprivation and sleep disorders represents a substantial problem for American society.
The problem appears to have deepened over time. Objective evidence about historical changes in sleepiness is hard to find, but there is some. A standard psychological test of personality, which has been regularly administered to large numbers of Americans since the 1930s, revealed that the proportion of men who felt tired during the day was significantly higher in the 1980s than it had been in the 1930s. And the average amount of sleep American students get has fallen by more than one hour over the past three decades. We seem to be a generally wearier bunch than our forebears.
Tired people are certainly common enough in the doctor’s waiting room. Physicians frequently encounter patients complaining of feeling tired all the time. The condition even has its own acronym, TATT. Of course not everyone who feels tired all the time is suffering from a lack of sleep. Chronic fatigue can result from anaemia, diabetes, cancer, depression and a whole host of other medical disorders. The distressing condition known as chronic fatigue syndrome (CFS), also referred to as myalgic encephalomyelitis (ME), is characterised by debilitating fatigue, pain in the muscles and joints, impairments in thinking and a general, horrible malaise. CFS is a distinct medical condition that cannot be attributed simply to lack of sleep. The origins of CFS remain controversial, but current theories focus on a combination of malfunctioning immune reactions and psychological factors.
CFS and other medical conditions undoubtedly account for some of the tiredness in society, but not much. The fact is that most people who feel tired during the day are just that – tired. They are tired because they have not been getting enough sleep. This explanation is so simple and so blindingly obvious that it is frequently overlooked.
Ordinary, everyday tiredness does not always require a medical explanation, but one is often sought nonetheless. ‘Exhaustion’ has become a voguish affliction of actors, pop stars and other celebrities. From time to time, a distraught and haggard celeb will flee to a clinic feeling, well, exhausted. The clinic duly subjects them to a battery of medical tests to establish whether they have diabetes, anaemia, ME or a thyroid disorder, while the media throb with stories about personal relationship problems, nervous breakdowns, exotic diets, exotic drugs, professional insecurities and emotional crises – just about everything, in fact, apart from plain tiredness. But given the long hours they are sometimes expected to work, plus the jet lag-inducing international travelling, it would be surprising if our stars of stage and screen did not occasionally feel very tired.
Another reason for believing that sleep deprivation is a common problem is that many of us get less sleep than we want or need, and considerably less than the proverbial eight hours we all supposedly aspire to. The evidence on this point is clear. For example, research found that in the 1990s young American adults were sleeping for an average of 7.3 hours a night. However, even this modest figure was inflated by weekend lie-ins: on weekday nights, Americans slept for an average of only 6.7 hours. A more recent study, which assessed the sleep patterns of middle-aged adults, found an average of only 6.2 hours. Similar conclusions have emerged from other countries. To give just a few illustrations, a survey in Poland found that adults there slept for 7.1 hours on workday nights, while Korean university students averaged 6.7 hours. When the Japanese Ministry of Health conducted a large survey they discovered that almost two thirds normally slept less than seven hours a night, and more than a quarter slept less than six hours. Worse still, half of Japanese high school students reported sleeping six hours or less on weekdays.
The research leaves little doubt that most adults in the USA, UK and other industrialised nations get substantially less than eight hours’ sleep most nights of the week, and many get less than seven. But does that matter? How much should we sleep?
The mythical inhabitants of Sir Thomas More’s idyllic island state of Utopia accorded sleep the priority it truly deserves. They slept for eight solid hours each night. Of the remaining 16 hours, work accounted for only six. (Sensible people.) The Utopians worked for three hours before noon then ate lunch; after lunch they rested for two hours, worked for another three hours then ate supper. They went to bed at about eight in the evening and slept for eight hours. The rest of each day they did as they pleased. Not quite the urban chic lifestyle, perhaps, but a refreshingly different perspective on life.
Conventional wisdom still holds that we need about eight hours of sleep a night. For most of us, however, the reality falls far short of the Utopian ideal, except perhaps at weekends and when we are on holiday. But is an average of, say, six or seven hours a night enough? Obviously, we cannot use Thomas More’s sixteenth-century fantasy as a scientific yardstick. So how do we judge the adequacy of sleep?
One approach is to ask people whether they think they are getting enough sleep. A recent study of more than twelve thousand adults did just that, and found that 20 per cent of them felt they were not getting sufficient sleep. Unsurprisingly, one of the factors most strongly associated with insufficient sleep was working long hours. Further evidence came from the Planet Project, said to be the largest opinion poll ever carried out. In 2000, an Internet-based survey was conducted with 1.26 million people in 251 countries. When asked how much sleep they needed in order to feel rested, 47 per cent of people replied eight hours or more. But when asked how much sleep they actually got, only 15 per cent reported sleeping eight hours or more, while 8 per cent said they got less than five hours a night. Many respondents reported having gone without sleep for long periods, whereas a mere 6 per cent said they had never missed a night’s sleep.
Six or seven hours of sleep a night is probably not enough for many people on a long-term basis. The experimental evidence suggests that the underlying sleep tendency for a typical healthy adult – that is, the amount of sleep they would take if completely liberated from work schedules and other constraints – is more like eight or eight and a half hours a night. This implies a shortfall of around an hour and a half each night. A shortfall of this size almost certainly matters. Restricting someone’s sleep by an hour and a half for just one night will measurably reduce their daytime alertness. The cumulative effects, when sleep is short-changed night after night, are far more pervasive. We shall be looking at the psychological and physical consequences of chronic sleep deprivation in the next two chapters.
A substantial nightly shortfall in sleep is difficult to sustain for more than five or six days in succession without sleepiness seriously impairing daytime alertness, mood and performance. This aspect of human biology might conceivably have contributed to the establishment of the seven-day week, comprising five or six days of work followed by one or two days of legitimised rest, as a standard unit of time. Most humans have been following the seven-day pattern for thousands of years. The seven-day week dates back to the pre-Biblical Sumerian and Babylonian civilisations. Right from the outset, one day of the week was deemed to be a day of rest and recreation. The Babylonians originally named their seven days after the five visible planets plus the Sun and the Moon, but the choice of seven otherwise has no objective basis in astronomy or any obvious feature of the physical environment. The Romans later adopted the seven-day week, dabbled with eight, then reverted to seven. The seven-day week appeared in the Bible, again with the inherent concept of a day of rest. According to the Biblical account of the Creation, God laboured for six days and rested on the seventh. Nowadays, people who work long hours and sleep for only six or seven hours a night really do need that extra time in bed at weekends to stave off sleep deprivation.
The thesis that many people are chronically sleep-deprived is not without its sceptics, however. Yvonne Harrison and Jim Horne at Loughborough University have argued that we all have the capacity to sleep more than we usually do, but only in the way that we can carry on eating after our physiological need for food has been satisfied. In support of their sceptical position, Harrison and Horne have cited, for example, an experiment in which healthy young adults slept for up to ten hours a night for two weeks, getting an extra hour or so of sleep each night. This additional sleep produced some improvements in their reaction times and a slight reduction in daytime sleepiness. However, there were no significant improvements in the volunteers’ subjective ratings of their own mood or sleepiness.
Scientists are paid to be sceptical, and counterblasts are an essential part of scientific debate. Nonetheless, such arguments must be set against all the other strands of evidence showing that chronic sleep deprivation is a real and widespread phenomenon. We have considered some of that evidence and there is more to come. First, though, what about you?
Are you sleep-deprived? (#ulink_5bc6e4af-67d9-577d-8861-8e93fe9ae0f7)
‘… Are you going to bed, Holmes?’
‘No: I am not tired. I have a curious constitution. I never remember feeling tired by work, though idleness exhausts me completely.’
Sir Arthur Conan Doyle, The Sign of Four (1890)
There is no universal, one-size-fits-all figure for the right amount of sleep. Individuals differ considerably in their sleep requirements. The conventional standard of eight hours a night is somewhat arbitrary, though not far off the mark for most people. But the best yardstick for you is your own preferred sleep duration. You can measure this by conducting a simple, if time-consuming, experiment on yourself. You will need two weeks of complete freedom from the tyranny of work schedules and alarm clocks, which means you will probably have to wait until your next long holiday (and possibly much longer if you have small children).
What you do is this. Every night for about two weeks, go to bed at approximately the same time. Make a note of the exact time just before you turn off the light to go to sleep. Then sleep to your heart’s content until you wake spontaneously the next morning – not with the aid of an alarm clock. Note down the time when you woke up and, ideally, a more precise time for when you think you fell asleep the night before. (All being well, this should have been within 10–20 minutes of turning out the light.) Your time of waking should be when you first became fully conscious, not when you eventually stumbled out of bed. Then calculate how long you spent sleeping. The experiment will work much better if you do not roll over after waking and doze for a further hour or two before getting up.
Ignore the figures for the first few days, because you will probably be sleeping longer to compensate for your prior sleep deficit. We tend to feel sleepy on relaxing holidays and at weekends because reality has finally caught up with us; when the usual pressures and stimulation that keep us going through the working week are suddenly removed, we sleep more to catch up on the backlog. This extra sleeping is only transitory, however. Once you have caught up and reached equilibrium you should start to feel livelier and more energetic during the day. Unfortunately, by that time the holiday has usually ended and the normal regime of late nights and early mornings resumes.
After a few days, your nightly sleep duration should settle down to a stable figure. Take the average over the final few days: this represents your preferred sleep duration. It should be somewhere between seven and nine hours, although not everyone fits this pattern. Unless you are elderly or have an unusually relaxed lifestyle, your preferred sleep duration will probably be longer than the time you normally spend sleeping. If the difference is very large – say, two or three hours a night – you could be storing up serious trouble for yourself.
Reasons for not sleeping (#ulink_b0ddfa16-24ea-5a90-9bba-8db66077f2c0)
Why all this sleep? – seven, eight, nine, ten hours perhaps – with a living to make, work to be done, thoughts to be thought, obligations to keep, a soul to save, friends to refrain from losing, pleasure to seek, and that prodigious host of activities known as life?
Walter de la Mare, Behold, This Dreamer. (1939)
Another reason for believing that sleep deprivation is widespread is that we sleep less nowadays than our ancestors did. There has been a major shift in sleep patterns in industrialised nations over the past century, the net result of which is less sleep.
William Dement of Stanford University has argued that humanity is in the midst of a ‘pandemic of fatigue’. Dement estimates that people in industrialised countries now sleep on average an hour and a half less each night than they would have done a century ago, and that most of us consequently walk around with an accumulated sleep deficit of 25–30 hours. If true, this means we would have to sleep for an extra two hours a night for two weeks to clear the backlog and return to equilibrium. Some of us come close to doing just that when we take a two-week holiday.
Lifestyles in industrialised societies have altered radically over the past century in ways that have consistently eroded the status of sleep and dreaming, leaving many of us now probably sleeping less than at any other period in human history. We live in an era when many people work long hours, where we have vastly more opportunities for entertainment and leisure, and where sleep is widely regarded as the poor relation to other pursuits. Humanity has inadvertently created lots of reasons for not sleeping.
One reason for not sleeping is that there is always so much work to do. Many sectors of society now work longer hours, on more days, than ever before. In early nineteenth-century Britain there were some 40 days in the year when the Bank of England shut its doors to observe saints’ days and anniversaries. By 1830 the number of such holidays had dropped to 18 days a year, and nowadays there are fewer than ten. Not only do we spend longer at work, we also spend longer getting to and from work, as commutes have grown both in distance and duration. Time spent stuck in a car or public transport is time that cannot be spent in bed. Ironically, the technological revolution has failed to free us from the shackles of paid work. Quite the reverse, in fact – it has given us the wherewithal to work more productively all day, every day. James Gleick made the point beautifully in Faster, his glorious exposé of our no-time-to-lose society:
Marketers and technologists anticipate your desires with fast ovens, quick playback, quick freezing, and fast credit. We bank the extra minutes that flow from these innovations, yet we feel impoverished and we cut back – on breakfast, on lunch, on sleep, on daydreams.
Cheap mobile communications enable us to stay in touch wherever we are, 24 hours a day. Copious amounts of caffeine, the world’s most popular psychoactive drug, help to keep us awake as we squeeze ever more into the day. The puritan work ethic and the cult of time management nag us to do a little bit more at the beginning and end of each day. So we get less sleep. But that is stupid, because people who cut back on their sleep achieve less and feel bad into the bargain. They end up stumbling through the day, fatigued and underperforming, without even realising what they are doing to themselves. They become, to quote one scientific paper, borderline retarded.
The idea of being able to get by on little or no sleep might appeal to some driven souls who would rather use the extra time for other things. (Some people seem to find being at work easier than living a real life.) In J. G. Ballard’s short story ‘Manhole 69’, a scientist who has entirely expunged the need to sleep from three human volunteers sneeringly declares that:
For the first time Man will be living a full twenty-four hour day, not spending a third of it as an invalid, snoring his way through an eight-hour peepshow of infantile erotica.
(Ballard’s sleepless volunteers, needless to say, meet a grisly fate.) If the fantasy of doing with less sleep ever became a reality – which, mercifully, it cannot – those extra hours of wakefulness would just be absorbed by more work. If we could all survive working 20 hours a day then the 20-hour day would become the norm. And we would still feel there were not enough hours in the day.
Fortunately, not everyone aspires to a sleepless world. A few highly successful businessmen have come out of the closet in recent years and openly admitted to sleeping for eight hours or more a night (although some cynics have pointed out that these captains of industry can only afford to have all that sleep because they are amply supported by minions working ridiculously long hours).
Britain is rapidly following the USA in becoming a fully-fledged 24/7 society where the consumer is king and nothing ever closes. Consumers really do want the freedom and flexibility to shop, bank or be entertained at any hour of the day or night, and governments are having to respond to their demands for public services to be continuously on tap, providing 24/7 facilities to the taxpayers who fund them. In 2001 the British government published a report called ‘Open All Hours’, explaining how public services were raising their game to meet the requirements of the 24-hour society. The report highlighted examples of how public services had responded to demands for extended opening hours. In his foreword, the Prime Minister wrote that ‘people living busy working lives … should be able to access services how and when they want’. The idea of modernising services to suit the needs and convenience of the public is surely laudable and uncontroversial. But there is something crucial missing from the cost-benefit analysis: the impact the 24-hour society is having on the ability of the people who are providing and consuming those services to get enough sleep.
Whatever happened to the technology-enabled revolution in leisure, which the future-watchers so confidently predicted in the 1960s? The main concern in those days was that we would all have too much free time on our hands, not too little. Sebastian de Grazia, one of the more thoughtful advocates from that era, argued for a return to the inner peace that can only come from a capacity for true idleness, combined with an escape from the constant stimulation that prevents people from ever being alone with themselves:
Perhaps you can judge the inner health of a land by the capacity of its people to do nothing – to lie abed musing, to amble about aimlessly, to sit having coffee – because whoever can do nothing, letting his thoughts go where they may, must be at peace with himself.
If the work ethic does not keep us from our beds, then our insatiable lust for entertainment and amusement surely will. As the Irish poet Thomas Moore put it, we are inclined to steal a few hours from the night:
’Tis never too late for delight, my dear;
And the best of all ways
To lengthen our days
Is to steal a few hours from the night, my dear!
In Shakespeare’s Twelfth Night the reprobates Sir Toby Belch and Sir Andrew Aguecheek have been up drinking all night. ‘I know to be up late is to be up late,’ contests Sir Andrew. ‘A false conclusion!’ avers Sir Toby: ‘To be up after midnight and to go to bed then, is early.’
The range of distractions and temptations to seduce us away from our beds has mushroomed since Shakespeare’s day. There is so much more to do in developed nations, and so much more wealth to do it with. The only quantity that has remained doggedly constant is the amount of time we have. There are still only 1,440 minutes in a day. So, we opt for the immediate fix of pleasure and stay up late. We know deep down that we will suffer the next day in mood, alertness and performance, but the lures are too appealing and their pleasures are instant.
Psychologists have a technical term – delayed gratification – to describe an individual’s ability to forgo an immediate reward in return for a bigger reward later on. It so happens that a capacity for delayed gratification is correlated with intelligence and attainment in life. Most of us, however, display a lamentable lack of delayed gratification when it comes to sleep. William Dement coined another term, ‘hedomasochism’, to describe the irrational belief that we can do it all, achieving ever more in our work, in our family lives and in our. leisure time, all at the expense of sleep. We cannot.
Ancient and modern (#ulink_f3cad88c-4ae4-5cd1-aa99-49261645811e)
We rise with the lark and go to bed with the lamb.
Nicholas Breton, The Court and Country (1618)
The current predilection for staying awake all hours is very recent in historical terms, let alone when measured against the span of biological evolution. It really took root following the invention of the electric filament light bulb by Thomas Edison in 1879, a negligible fraction of an instant ago in evolutionary terms. Of course, people did stay up after dark in the days before cheap electric lighting – just much less.
There have only ever been two ways for humans to deal with the night: to sleep and doze through it or to light it artificially. Until the nineteenth century the only practical source of artificial light was fire in one form or another. When humans depended on expensive candles or oil for artificial light they went to bed earlier and stayed there longer, unless they were in the wealthy minority. Few people did much work after dark. And when they did use artificial lighting, the fires and candles (and later, the gas mantles) generated light of insufficient intensity to reset their internal biological clocks in the way that much brighter electric lighting can. One electric light bulb produces as much light as a hundred candles and for only a tiny fraction of the cost. Unlike our ancestors, we no longer have to sleep, doze or stay in bed just because it is dark.
To appreciate how different life was for the majority of people living in temperate or northern climates, we need only wind the clock back to the eighteenth century. For most working folk, especially in winter, the sun provided the only serious illumination. The Natural History of Selborne, which was written by an English country clergyman called Gilbert White and published in 1788, describes life in a small village in rural England. White’s parochial history is said to be the fourth most published book in the English language. In one of his glimpses into the lives of Selborne’s human inhabitants, White reminds us that in the days before electric lighting, few people could afford the luxury of routinely staying awake for long during the hours of darkness. The villagers burned rushes to produce light, and even rushes cost money:
Working people burn no candle in the long days, because they rise and go to bed by daylight. Little farmers use rushes much in the short days, both morning and evening in the dairy and kitchen; but the very poor, who are always the worst economists, and therefore must continue very poor, buy an halfpenny candle every evening, which, in their blowing open rooms, does not burn much more than two hours. Thus have they only two hours’ light for their money instead of eleven.
In rural northern Europe of the Middle Ages it was pointless or impossible to work the fields during the dark days of winter, and too costly to heat and light the home all day. Whole families would therefore take to their beds for days at a time. You might not relish the prospect of spending days in bed with nothing to do. (Or perhaps you would?) Boredom would be the big enemy. Boredom, however, is a modern concept. Being alone with our thoughts and dreams is no longer enough for us.
Cold weather was another good reason for staying in bed, as Samuel Pepys recorded in this entry from his diary, written in December 1661:
All the morning at home, lying abed with my wife till 11 a-clock – such a habit we have got this winter, of lying long abed.
But even in warm, sunny climates, our ancestors probably spent more of their time in bed, especially in civilisations that practised the siesta.
In modern industrialised societies we are exposed to an artificial day that is extended by electric lighting and typically lasts for at least 16 hours, regardless of season. The marked seasonal fluctuations in the conception rate, which were once associated with the long winter nights, have almost disappeared now. Moreover, we now pack all of our sleep into a single block of time during the remaining seven or eight hours of darkness. This pattern of sleeping is biologically unusual: in most other species, sleep is split into two or more separate episodes in each 24-hour period. As we shall see, there are reasons for supposing that humans have not always slept in a single, compressed block.
Our daily cycle of sleep and wakefulness is largely determined for us by clocks rather than tiredness. Many of us go to bed when it is time to go to bed, not when we are tired, and wake when we have to wake, not when we choose to. Clocks with minute hands did not become available until the seventeenth century. Until quite recently in history, the majority of people relied on the sun for their timekeeping and lived in a world where the light intensity changed gradually at dawn and dusk, not instantaneously with the flick of a light switch. Moreover, they did not work in offices, factories or shops where they were required to be present at a certain time early every day.
How do humans sleep when left to their own devices in a world where it is dark for more than half the day – as would have been the case in pre-industrial northern countries during winter? To find out, Thomas Wehr at the National Institute of Mental Health in Maryland exposed volunteers to an experimental environment where it was dark for 14 hours a day and they could sleep freely. To begin with, the volunteers slept a lot (some more than 12 hours a day) as they caught up on their backlog. On average, they clocked up an additional 17 hours of sleep during the initial adjustment period. After their sleep deficits had been paid off, they settled down to an average sleep duration of eight and a quarter hours a day. Their mood and energy levels during the day improved consistently over the course of the experiment. When they were awake, they felt more awake and were more awake.
As well as sleeping longer, Wehr’s subjects also slept differently. Under these conditions of long, dark days and with nothing much to do, their sleep spontaneously divided into two distinct blocks. Typically, they would lie in a state of quiet rest each evening for about two hours before falling asleep. Then they would sleep for about four hours, usually waking at the end of an episode of dreaming. After another couple of hours of quiet rest they slept for a further four hours. On waking in the early morning they would lie in quiet rest for another couple of hours before rising.
Under these pseudoprimitive conditions, then, sleep was preceded, punctuated and terminated by long periods of quiet restfulness. This pattern of sleeping in two distinct blocks of time is known as biphasic sleep. It is typical of many mammals living in the wild and was probably the natural sleep pattern of our ancestors. We all retain the biological capacity for biphasic sleep, despite the profound changes in humanity’s environment since the advent of artificial lighting and the 24-hour society. A group of thoroughly modern Americans reverted to biphasic sleep within days of being given the opportunity. The nearest contemporary equivalent is the afternoon sleep of the siesta, a custom that still survives in some countries.
The predominant lifestyles of artificially-lit industrialised societies have led us to compress our sleep into a single block of seven or eight hours, as though we were living permanently in midsummer (but usually without the siesta). We have jettisoned the additional hours of quiet rest and the seasonal variations that once accompanied human sleep. We have also lost the main channel that once existed to our dreams. During the 14-hour nights, as they alternated between sleep and quiet rest, Wehr’s volunteers usually awoke from dreaming, giving them ample opportunity to lie quietly in the dark and contemplate their dreams. In later chapters we shall consider why dreaming evolved and what it does for us.
A quite different reason for believing that many people nowadays are chronically sleep-deprived is the mass of evidence that sleepiness is a major cause of accidental injuries and deaths. We shall now look at how sleepiness jeopardises safety-critical activities such as driving a car, flying an aeroplane, being a doctor, running a country and operating a nuclear power plant.
Sleepy drivers (#ulink_46e0c30e-4abe-5fe4-b6e1-a242f0727cef)
Till o’er their brows death-counterfeiting sleep
With leaden legs and batty wings doth creep.
William Shakespeare, A Midsummer Night’s Dream (1595–6)
Accidents are one of the leading causes of death in developed nations, and sleepy people are responsible for many of them. A remarkably large proportion of vehicle accidents are the direct or indirect result of tired drivers losing concentration or falling asleep at the wheel. A few examples may give a flavour of the carnage they cause. In March 1994 near Barstow in California, a pickup truck carrying 20 people veered off the road and crashed into a culvert after the driver apparently fell asleep at the wheel. The driver survived but 12 passengers died. In July 1995 near Roquemaure in France the driver of a bus carrying Spanish students from Amsterdam to Barcelona seemed to nod off then wake abruptly as his bus scraped a passing truck. He lost control and the bus swerved wildly before rolling over several times. The accident caused 22 deaths and 32 injuries. In February 2001 a sleep-deprived driver caused the Selby rail disaster in the UK, after he fell asleep at the wheel and his vehicle crashed onto a railway line. Ten train passengers died. The driver, Gary Hart, admitted getting no sleep the night before the crash, but claimed he could still drive safely. He was sent to prison.
Scientists have judged that sleepiness is a factor in at least 10 per cent of fatal car crashes in the USA and more than 50 per cent of fatal crashes in which a truck driver is killed. A 1994 report by the US National Commission on Sleep Disorders concluded that driver fatigue contributed to 54 per cent of all vehicle accidents in the USA. A comparable situation applies in the UK and elsewhere. Research concluded that at least 10 per cent of vehicle accidents in the UK are related to sleepiness, though some experts have put the figure much higher. Two large surveys in England found that sleepiness was a causal factor in 16 per cent of accidents to which the police were summoned and at least 20 per cent of accidents on motorways. Driving on a motorway is generally more monotonous than driving on a minor road, and monotony heightens the risk that a tired driver will fall asleep at the wheel. Half the drivers involved in these sleep-related accidents were men under the age of 30 and many of the accidents involved truck drivers, company cars or workers returning home from night shifts.
For every sleepy driver who actually crashes there are uncounted numbers who have had near misses. A large survey by the British Transport Research Laboratory found that 29 per cent of drivers had come close to falling asleep at the wheel within the previous year, while other research established that at least 5 per cent of middle-aged male drivers had actually fallen asleep while driving on several occasions. Not surprisingly, drivers suffering from moderate or severe daytime sleepiness are at least twice as likely to have a vehicle accident.
The official statistics tend to underestimate the true extent of the sleepiness problem, and it is easy to see why. Drivers who survive crashes are naturally reluctant to admit that they dozed off at the wheel, even if they recollect doing it. And it is difficult to prove legally that sleepiness caused a crash (especially if the driver is dead). Unlike alcohol, drugs or mechanical defects in a vehicle, sleepiness leaves few evidential traces. You can easily measure how drunk someone is at the roadside immediately after an accident. But measuring sleepiness is neither quick nor easy, and in practice it is simply not done.
The systematic under-reporting of fatigue was highlighted by accident statistics for Italian highways. Over the period from 1993 to 1997 the Italian authorities officially ascribed the cause as sleep in only 3 per cent of accidents. However, by analysing the data in more depth, researchers were able to estimate that sleepiness had probably contributed to about 22 per cent of accidents. If true, this means that the official statistics had underestimated the hazard of driver sleepiness by a factor of seven.
The time of day is a major element in the relationship between sleepiness and accidents. Thanks to our natural circadian rhythms, we all feel sleepier at certain times in the 24-hour cycle (usually in the early hours of the morning and again in the afternoon) regardless of how much sleep we have had. As expected, sleepiness-related vehicle accidents occur most often in the early hours of the morning and in the afternoon, during these natural peaks in sleepiness. Older drivers are particularly susceptible to afternoon sleepiness, whereas younger drivers are more prone to crashing late at night or in the early hours. When researchers analysed the data for accidents in which the driver had been injured or killed (excluding those involving alcohol) they found that young drivers were between five and ten times more likely to crash late at night than during the morning.
Driving late at night poses a risk for train drivers as well. In one study, scientists monitored train drivers while they drove the same route, both by day and at night. The train drivers felt much sleepier when driving at night, and physiological measurements mirrored their subjective feelings. Their brain waves, heart rates and eye movements at night were all characteristic of sleepy people. Four of the 11 drivers who were monitored admitted to dozing off during the night journey and two of them failed to respond to signals. Sleepiness has almost certainly caused numerous rail crashes over the years, but again the official statistics have systematically underestimated its importance.
The sleepiness experienced by many drivers is partly a product of natural cìrcadian variations in wakefulness. But much of the blame rests with simple lack of sleep. And when lack of sleep is combined with driving at odd hours, the effect can be lethal. Prevailing social attitudes towards this issue are frankly perverse. Many parents think nothing of packing their family into a car and then driving long distances to a holiday destination while they are seriously tired. They would be horrified at the thought of doing this while drunk, but the effects of tiredness and alcohol on their ability to drive safely are strikingly similar, as we shall see in the next chapter. The number of drivers involved is large. In August 1996 French researchers assessed the extent of sleep deprivation among drivers during the holiday season, by randomly stopping two thousand cars at tollbooths and interviewing the drivers. It transpired that half of them had slept less than they would normally have done during the previous 24 hours. On average, these happy holidaymaking drivers had slept for 3.4 hours less than normal.
Many long-haul truck drivers get insufficient sleep, with potentially serious consequences for their performance and safety. When investigators studied truck drivers working in the USA and Canada they found that the drivers spent on average slightly more than five hours a day in bed and got slightly less than five hours’ sleep. This was much less than their self-reported ideal of more than seven hours a day. Nearly half the truck drivers augmented their sleep by napping, but the naps were not sufficient to compensate. Video and EEG brainwave recordings revealed that more than half the drivers had at least one period of drowsiness while they were driving, and two actually fell asleep at the wheel.
Even changing the clocks can be dangerous. The switch to daylight-saving time each spring reduces the length of one night by one hour, which slightly disrupts sleep routines for the next few nights. The extra sleepiness caused by even this apparently trivial disturbance is enough to generate a statistically significant seasonal rise in traffic accidents. Fatal accidents peak on the day immediately following the changeover. Alcohol-related accidents also rise during the week after the clocks change, probably because the effects of alcohol and sleepiness reinforce each other.
You might think that changing clocks in the opposite direction each autumn would have the reverse effect, but you would be wrong. When researchers analysed 21 years of US vehicle accident statistics, they found that the switch back from daylight-saving time each autumn was also accompanied by an increase in fatal accidents – despite the fact that in this case everyone got an extra hour in bed. The likely explanation is that many people anticipated the extra hour in bed by staying up even later the night before. This was borne out by the fact that the rise in fatal accidents around the autumn changeover was most marked just before the clocks changed, and especially in the early hours of the morning.
One of the most alarming aspects of daytime sleepiness is that we can fall asleep briefly without even noticing. You are unlikely to be aware that you have slept unless your sleep has lasted for at least a couple of minutes. Tired people can therefore fall asleep at the wheel of a speeding vehicle for tens of seconds at a time and never even know. Researchers measured this phenomenon by waking volunteers after daytime naps of varying durations and asking them if they had been asleep. (Their sleep was confirmed by objective physiological measures.) After one minute of sleep only 15 per cent of subjects had any awareness that they had been asleep, and only 35 per cent were aware even after five minutes of sleep. The upshot is that so-called microsleeps, lasting anything up to a minute, often go unnoticed. Suppose a sleepy driver lapses into a microsleep for only ten seconds while driving on a motorway at 70 miles an hour. During that brief, unnoticed lapse in waking consciousness the vehicle will cover about 70 car lengths. It is virtually certain that while you are reading these words someone, somewhere is microsleeping at the wheel of a speeding vehicle.
One apparent obstacle to prosecuting drivers who fall asleep at the wheel is proving that they were aware of their dangerous state and are therefore legally responsible for their actions. No one could reasonably claim to have been completely unaware that they were dangerously drunk, but a driver might conceivably claim to have been oblivious of being sleepy before crashing. However, the experimental evidence suggests otherwise. Sleep does not occur spontaneously without prior warning in the form of sleepiness.
Drivers who fall asleep at the wheel may not recall the actual moment of falling asleep, but they will almost certainly remember feeling sleepy beforehand. Scientists established this by monitoring sleep-deprived volunteers while they drove a simulator. The sleepier the drivers felt, the more mistakes they made. Serious errors, of the type that might have caused a crash in real life, were always preceded by prolonged feelings of sleepiness. By the time an ‘accident’ took place the tired driver had invariably been consciously fighting sleepiness for some time. The strong implication is that drivers who fall asleep at the wheel in real life will almost certainly have felt noticeably sleepy beforehand. The problem is that so many sleepy drivers press on regardless, fighting their sleepiness and risking lives. Many drivers harbour the illusion that they will not fall asleep at the wheel provided they fight hard enough. What they fail to appreciate is that if you are sufficiently sleepy you will eventually fall asleep, no matter how hard you resist.
Not all sleepy drivers are sleepy because of sleep-deprived lifestyles. Some are sleepy because they have a medical sleep disorder, often undiagnosed. The most common of these, called sleep apnoea, involves the repeated interruption of breathing during sleep. We shall be taking a closer look at sleep apnoea in chapter 15. Individuals who suffer from this disorder can become severely sleep-deprived, although they rarely know why. The daytime sleepiness caused by the repeated disruption of their sleep every night can severely impair their driving performance.
Sleepy drivers not only have more accidents, they also have worse accidents. The hallmark of an accident caused by a driver falling asleep at the wheel is the absence of skidmarks. Of all the crashes that are attributed to drivers falling asleep, more than three quarters involve the car driving off the road and more than half involve high speeds.
Car and truck manufacturers have done little to tackle the safety hazard created by sleepy drivers. Driver fatigue remains one of the biggest weak spots in vehicle safety, perhaps because it is much easier to modify the design of a vehicle than to modify the behaviour of humans. However, some promising technology is being developed that may show the way. One system uses cameras mounted in the dashboard to track the driver’s eye movements. It exploits the fact that people blink in a characteristic way when they are about to fall asleep. The device warns the driver if the blink frequency indicates a risk of nodding off at the wheel. IBM is developing an even more sophisticated system, known as the Artificial Passenger. An intelligent computer, which knows the driver’s personal profile and interests, holds a conversation with the driver. It asks questions and even tells jokes (though humour is reportedly not yet one of its strengths). If the driver’s responses are slow, flat in intonation and fail to make sense, the Artificial Passenger may judge that the driver is sleepy and urgently needs to be revived. If so, it will automatically open one of the car’s windows, sound an alarm or even activate a device that sprays cold water in the dozing driver’s face.
Governments are only just beginning to wake up to the carnage caused on our roads by sleepiness, having focused for so long on the dangers of alcohol. And yet sleepiness accounts for far more road deaths than alcohol, let alone drugs.
Sleepy pilots (#ulink_dc39c136-f720-5caf-bff8-d732597e2a37)
My spirits grow dull, and fain I would beguile
The tedious day with sleep.
William Shakespeare, Hamlet (1601)
Fatigue and chronic sleep deprivation are obviously of crucial relevance to aviation safety. Tired pilots are bad pilots, for all the reasons that tired drivers are bad drivers. How big is the problem in practice?
Historically, severe fatigue among aircrews has sometimes been a major problem during crises where huge demands have been placed on precious personnel. Take, for example, the Berlin airlift of 1948–9. In June 1948 the forces of the former Soviet Union occupying eastern Germany began a blockade of road, rail and other communications between Berlin and the West. An international crisis ensued. The USA and UK mounted a huge airlift operation to supply West Berlin with food and other essential supplies. The airlift continued for 11 months until the Soviets eventually withdrew their blockade. During that time Allied planes delivered more than two million tons of food, fuel and other supplies to the beleaguered residents of West Berlin. To sustain this huge effort, the aircrews worked punishing schedules with grossly inadequate sleep. There were many accidents, some of them the result of fatigue. A special investigation during the crisis led to immediate improvements in the aircrews’ working conditions and sleeping quarters, which probably made a material contribution to the ultimate success of the whole operation.
Even in peacetime, tiredness is not unknown on the flight deck. Most airline flight crews experience some sleepiness and impairment in their performance, especially during long-haul and overnight flights. In one recent study, scientists from the British Defence Evaluation and Research Agency monitored 12 airline pilots during routine nine-hour flights between London and Miami. Recordings of their EEG brain-wave activity and eye movements revealed that 10 of the 12 pilots either slept or displayed signs of significant sleepiness during the flights. These episodes were often brief, lasting less than 20 seconds. Microsleeps of this brevity generally go unnoticed, and the pilots would probably have been unaware of drifting off.
Scientists from the NASA Ames Research Center in California also detected fatigue among flight crews on commercial long-haul flights. The crews on these flights, which crossed up to eight time zones, became measurably sleep-deprived. They felt more fatigued than normal, consumed more caffeine, ate more snacks and reported more minor health problems such as headaches, nasal congestion and back pain. Their sleep loss was made worse by the fact that their circadian rhythms did not have time to synchronise with local times. Their natural low points in alertness therefore often occurred while they were on duty, amplifying their sleepiness.
Jet lag is not just unpleasant and stressful – it also has physical effects on the brain. Researchers compared two groups of female flight attendants who had all been working on long-haul flights for at least five years. Half the women were in jobs that allowed them two weeks to recover between long-distance flights, while the other half usually had only a few days’ rest in between. The women who had little time between flights performed significantly worse on tests of learning and memory; their reactions were slower and they made more mistakes. More significantly, brain scans revealed distinct physical changes in their brains. A region of the brain known as the right temporal lobe had shrunk significantly. The women with the most shrunken right temporal lobes also had the highest levels of cortisol, a stress hormone that is known to affect the structure of the brain and the functioning of the immune system.
The implication of this research is that people who regularly fly long distances, crossing more than six or seven time zones, should ideally allow at least ten days to recover before doing it again. The research also raises questions about the policies of airlines that require their flight crews to fly long haul without adequate rest periods in between. The thought of sleepy, jet-lagged pilots with wizened right temporal lobes and impaired mental abilities slumped behind the controls of jumbo jets is mildly alarming.
Flying for a living can be tiring even when it does not involve crossing multiple time zones and becoming jet-lagged. Like workers in many other industries, flight crew are often required to start work early in the morning, and this alone can starve them of sleep. Researchers who monitored the sleep of female cabin crew found that when the women worked early mornings their sleep was reduced to an average of just over five hours. This is not enough sleep for the vast majority of people. Early-morning working was also unpleasant and mildly stressful for these women. They reported feeling apprehensive about having to rise early, they felt sleepy during the day and they complained more about their sleep being unrefreshing.
The only cure in situations like these is getting enough sleep, and at the right time of day. But that is not always possible on long-haul flights. Napping can provide a short-term palliative. If all else fails, a British firm has patented a technological aid to keep airline pilots awake. Worn like a wristwatch, it uses a motion sensor to monitor the pilot’s movements. A loud alarm sounds if there has been no movement for a few minutes. Personally, I would prefer not to find myself on a plane flown by a pilot who needs one of these devices. But if I do, I hope it works.
Space flight is even less conducive to sleep than air travel. Astronauts can and do sleep in space, but not very well. Space flight confuses the body’s internal clock and reduces both the quantity and quality of sleep. Astronauts on the Space Shuttle were typically getting only five or six hours of poor quality sleep a night, and often resorted to sleeping pills. More than 40 per cent of Space Shuttle astronauts took medication for sleep disturbances – about the same proportion as took drugs for motion sickness.
In recent years, NASA has been giving its astronauts doses of the ‘sleep hormone’ melatonin to help them sleep. (We shall see what melatonin does in chapter 6.) However, research by Charles Czeisler at Harvard Medical School found that melatonin actually had little beneficial effect on astronauts’ sleep. What did work, however, was covering the astronauts in electrodes to monitor their sleep. Czeisler discovered that Space Shuttle astronauts slept better when they were festooned with electrodes and physiological monitoring equipment. The most likely explanation is simple and psychological. The astronauts had probably been sleeping badly because they were so focused on performing their many duties. Swathing them in sleep-monitoring electrodes convinced them that sleep was also a legitimate and important part of their duties, and they consequently relaxed and slept better despite the marginal discomfort.
Sleepy doctors (#ulink_4696b113-aab3-5fcc-b50a-d8a6f9cdbc08)
Think not, is my eleventh commandment; and sleep when you can, is my twelfth.
Herman Melville, Moby-Dick (1851)
To find the prime example of skilled professionals who routinely perform demanding, safety-critical tasks while severely sleep-deprived we need look no further than medicine. Chronic sleep deprivation is rife among hospital doctors, who are not superhuman enough to be immune from its consequences. Lack of sleep impairs their mood, judgment, decision making, thinking abilities and communication skills just like anyone else. One commentator recently described medical training in the USA as ‘a gruelling endurance test in which patients are often those most at risk’. The situation in the UK is no better.
Just how tired are doctors? According to the research data, some of them are very tired indeed. A study of American physicians undergoing postgraduate medical training illustrates the problem. During a typical 36-hour period of on-call duty, the interns spent less than five hours in bed and slept for an average of less than four hours. That is not enough. Another American study found that three out of four residents in obstetrics and gynaecology were working between 61 and 100 hours a week, and more than two thirds reported getting less than three hours’ sleep while on night call. Perhaps unsurprisingly, a large majority wanted limits placed on their work hours, despite concerns that this might restrict their professional experience. Much the same is true for doctors in other countries. For instance, house officers in Stockholm hospitals were found to sleep for an average of only four hours when on night call.
Three or four hours’ sleep is not enough for most people. Research has shown that doctors who have slept for less than five hours in the previous 24 display significant deteriorations in their memory, intellectual skills, language and numeracy. Doctors working night shifts get less sleep than those on day duty, and their performance is consequently worse. A study at Stanford University found that emergency physicians slept for an average of 6.3 hours after working day shifts, but only 5.2 hours after night shifts. Their performance and mood suffered accordingly: those working nights had slower reaction times and took one third longer to perform a standard medical procedure. Their performance deteriorated during the course of a night shift and they became progressively more likely to make mistakes. They also felt less alert, less motivated, less happy and less clear-thinking than when they were on day shift. Given the choice, any sane patient would want to be treated by a doctor working day shifts.
As we shall see in the next chapter, sleep deprivation has a big impact on tasks requiring sustained concentration and effort. But tired people are often able to perform simple or engaging tasks in short bursts. Sleep-deprived doctors usually cope surprisingly well with brief but invigorating crises. Problems are more likely to arise with routine, repetitive tasks requiring prolonged attention. It might be relevant that the impact of sleep deprivation is found to vary somewhat between the different medical specialities, with surgeons being the least affected.
We will also see in the next chapter that sleep deprivation erodes our mood, motivation, social skills, communication skills, creativity and lateral thinking. Again, doctors are no exception. Psychologists who assessed junior doctors after a night of dealing with emergency admissions found deteriorations in their mood and motivation, as well as the usual impairment in short-term memory. Sleep-deprived doctors also perform significantly worse on measures of creative thinking and originality. They are less capable of solving complex problems that require originality and non-linear thinking, such as diagnosing an unusual condition.
To put icing on the cake, sleep-deprived doctors have an alarming tendency to fall asleep when driving their cars. An American study of paediatricians found that half of them admitted to having fallen asleep while driving, almost always after a night on duty. The on-call doctors notched up substantially more traffic accidents and traffic citations than their faculty colleagues. Their propensity to fall asleep at the wheel was unsurprising, considering they got less than three hours of sleep during on-call nights. So, after unintentionally jeopardising their patients’ lives while on duty in the hospital, sleep-deprived doctors put themselves and other road users at risk while driving home.
The madness of politicians (#ulink_70d805b8-dea4-5f00-9651-d4c1102fa389)
I have noted as something quite rare the sight of great persons who remain so utterly unmoved when engaged in high enterprises and in affairs of some moment that they do not even cut short their sleep.
Michel de Montaigne, ‘On Sleep’, Essays (1580)
Long hours and inadequate sleep are standard features of political life. Those highly motivated, hardy individuals who survive the fierce competition and reach the top must have an above-average capacity for coping with little sleep. Having got to the top, they then set a bad example to the rest of us by projecting an image of tireless and unceasing industry. To accuse a politician of looking tired is frankly insulting. But they are only human, and inside that aura of sleeplessness there often lurks a tired person who secretly wants to spend more time asleep in their own bed.
Mythology and image-making abound when politics meets sleep. During Margaret Thatcher’s tenure as prime minister an absurd myth was fostered that it is both feasible and admirable for people routinely to sleep for only four hours a night and work hard for the remaining twenty. Hogwash. With the possible exception of a tiny minority of extraordinary individuals, humans simply do not thrive or perform well for long on four hours’ sleep a night.
Negotiators sometimes deliberately exploit the debilitating effects of acute sleep deprivation to achieve their aims. People who have hardly slept for two or three days will agree to almost anything at four o’clock in the morning. Dragging out negotiations over several days may be irksome, but it can work if you make sure your side gets more sleep than the opposition. But more often than not, tiredness just gets in the way of rational politics. In 1997, after a sleep-deprived marathon of negotiation, representatives of 160 nations agreed the Kyoto Protocol, aimed at reducing global emissions of greenhouse gases. Three years later, fatigue helped to set back the environmental cause. In November 2000 an international summit convened in The Hague to thrash out unresolved problems left hanging by the Kyoto treaty. The negotiations ground on for 12 long days, leaving the delegates exhausted. In the early hours of the morning on the final day the British deputy prime minister, John Prescott, proposed a deal that he thought would break the logjam. But the deal collapsed, reportedly because the French delegate refused to make a difficult decision. A furious Prescott laid the blame squarely on the French environment minister. He told journalists: ‘She got cold feet, felt she could not explain it, said she was exhausted and tired and could not understand the detail and then refused to accept it. That is how the deal fell.’ The summit ended without reaching agreement.
The burden of work on the politicians and officials who run our nations has grown inexorably over the years. The number of decisions they must take has mushroomed, as the world has become an ever more complex, law-bound and media-scrutinised place. The insatiable demands of the 24-hour news media add greatly to the load. Political leaders are frequently overloaded, with insufficient time to think and formulate policy, let alone get enough sleep.
Academic observers of the British government scene calculated that between the 1960s and the 1990s the average working day for government ministers grew from 14 hours to 18 hours. The eminent political historian Peter Hennessy described the job of a British cabinet minister as ‘a conveyor belt to exhaustion and underachievement all round’, while a former senior adviser to the prime minister wrote that ‘Ministers are governed by diaries which seem designed to break them in physique or spirit in the shortest possible time.’
The diaries of the late Alan Clark, who served as a government minister in the 1980s and early 1990s, give illuminating glimpses into the sheer grind of ministerial life. Clark observed colleagues who were ‘boss-eyed’ with fatigue after working past midnight. One diary entry from 1984 describes how the civil servants would always find more work for him to do, no matter how little sleep he had had:
Today has been vilely full. Went early to Leicester after a late, late vote and impossible to drowse in the train as officials were watching me beadily in case (their excuse) anything in the brief ‘needed explaining’. I dropped off, as good as, several times during monologues at the various offices.
To add to the hazards of politics, Clark’s life was occasionally jeopardised by an exhausted government driver who had a tendency to nod off while conveying the minister along motorways at antisocial hours. Alan Clark’s experiences were by no means unusual. Geoffrey Howe, who was Foreign Secretary in the 1980s and who, like Alan Clark, worked under the notoriously unsleeping eye of Margaret Thatcher, described his gruelling work regime like this:
During six years at the Foreign Office I took home, to work through overnight while others slept, no less than 24 tonnes of paper … Six o’clock was my normal time for getting up. My average bedtime was about four hours earlier.
The long-hours culture affects not only the elected politicians but also the officials who serve them (and, some would claim, run the country). Sir John Coles, who was head of the British Diplomatic Service from 1994 to 1997, described the problem like this:
Long working hours, pressure and flurry were part of Foreign Office culture. We liked to feel busy and under pressure … But it became necessary to question some of this culture. These things did not necessarily lead to good policy. Tired, pressurised officials were liable to make mistakes.
The demands now are, if anything, even greater. In December 2000 Tony Blair was asked, during an Internet chat forum with members of the public, what he remembered dreaming about on the night after his first general election victory in 1997, and what was the last dream he remembered. The prime minister’s answer was revealing about the punishing lifestyle that goes with his job:
I don’t remember getting much sleep at all that night … After a couple of hours’ sleep, we were up early to prepare for going to Buckingham Palace. As for dreams, I’ve not had much chance for sleep over the past few days, let alone dreams.
Jet lag caused by frequent international travelling adds to the problem. In the immediate aftermath of the terrorist attacks in the USA on September 11, 2001, Tony Blair engaged in a gruelling programme of shuttle diplomacy that saw him travel more than 40,000 miles on 31 international flights in the space of a few weeks. And the fact that he then looked tired made the front pages of the newspapers.
British Members of Parliament work some of the strangest, if not the longest, hours of any legislature in the world. In October 2000 The Times published the results of one of the most detailed surveys ever carried out into MPs’ lifestyles. The survey revealed a nightmarish world of long hours and chronic sleep deprivation. Most MPs said they worked between 71 and 80 hours a week, with one in six working up to 90 hours a week. One government minister logged a working week of 91 hours in Westminster followed by 20 hours at the weekend, leaving an average of eight hours a day for everything else including travelling, family life and a little sleep.
The response from one MP was illustrative. The constituency he represented, and where his family still lived, was a long way from London. He would leave home at five a.m. on a Monday morning and return in the small hours of the following Friday morning. His weekend at home would be spent on constituency business, and then there were the occasional foreign trips with a parliamentary committee. He and his partner planned to go out together on Saturday nights but he was usually so tired by then he would fall asleep. Once, while driving home from London, he had almost fallen asleep at the wheel and crashed. There has been some modernisation of parliamentary schedules, in response to pressure from MPs, but the long-hours culture remains deeply embedded.
Some politicians cope with the long hours with the assistance of drugs of various kinds. In the USA, coke is a favourite – particularly the diet cola variety. During the US presidential election campaign in 2000, candidate Al Gore engaged in an electioneering programme of awesome intensity, involving 19-hour days and an itinerary that criss-crossed the continent. ‘Our campaign consists of a lot of long days and a lot of short nights,’ said Gore’s spokesman. ‘While some candidates may look for their feather pillows, Al Gore is looking for every single undecided voter he can find.’ To help him remain awake and vaguely sentient, Gore reportedly drank copious amounts of Diet Coke. One of his aides was explicit about the reason: ‘These are high-caffeine days. He needs his fuel to get through them.’ Sadly for Gore, the caffeine was not enough.
George W. Bush, who beat Al Gore by the slimmest of slim margins, became notorious during the election campaign for his verbal fluffs and tortured syntax. Whole books have been dedicated to Bush’s gaffes, malapropisms and garbled sentences. One American psychologist even suggested that Bush’s difficulties with the spoken word resulted from a lack of sleep in someone who apparently needed a lot of it.
Perhaps the defeated Al Gore could draw a minuscule crumb of comfort from an informal survey, which was conducted several months after the presidential election and reported to the International Conference for the Study of Dreams in July 2001. This survey found that conservative Republican supporters were nearly three times more likely to experience nightmares than their less conservative Democrat opponents. Half of the dreams recalled by Republicans were nightmares, compared with fewer than one in five of Democrats’ dreams. Moreover, the conservatives’ dreams were generally more frightening and more aggressive in content.
When the next big crisis erupts on the world stage, remember this. The politicians and officials who will be handling that crisis will be getting little sleep, perhaps for days at a time, and they will consequently become even more sleep-deprived than they already were. Their reactions, judgment, rationality, mood, memory, creativity and social skills will deteriorate, and they will become more prone to taking inappropriate risks. You might conclude that the world would be a safer and saner place if our leaders and their officials spent more time in bed (asleep).
Truly, madly, sleepily (#ulink_066d4b93-ca47-5819-88e3-8f715972c0e7)
I have an exposition of sleep come upon me.
William Shakespeare, A Midsummer Night’s Dream (1595–6)
The human errors caused by tiredness sometimes have truly catastrophic consequences, and there have been plenty of man-made disasters to prove it.
Tiredness lay behind the environmental disaster that occurred when the supertanker Exxon Valdez ran aground in Prince William Sound, Alaska, spilling 11 million gallons of crude oil into the pristine waters and polluting thousands of miles of shoreline. The official investigation by the US National Transportation Safety Board concluded that sleep deprivation was a direct cause. The accident took place just after midnight on 24 March 1989, when the Exxon Valdez was under the control of the third officer. He had slept for only six hours during the preceding 48 hours and was therefore substantially sleep-deprived. It appears that he fell asleep on duty. Media reporting at the time suggested that alcohol was to blame for the accident, but the real culprit was fatigue. In addition to the appalling environmental damage, one man’s tiredness cost his employer more than five billion dollars in punitive damages.
Tiredness contributed to the US Space Shuttle Challenger disaster. On a freezing cold morning in January 1986 the Challenger ascended for ten miles and then exploded, killing the crew of seven astronauts. It later emerged that crucial rubber O-ring seals had failed catastrophically at the low temperatures prevailing that morning. The US Presidential Commission that investigated the disaster concluded that there had been serious flaws in the decision-making processes leading up to the launch. The danger had been foreseeable, but tiredness had contributed to the bad decision to launch despite the icy conditions. Key managers had slept for less than two hours the night before and had been on duty since the early hours of the morning. They were at a dangerously low ebb when the fateful decision to launch was taken. The official report noted that ‘fatigue is not what caused the accident, but it didn’t help the decision-making process’. It also commented that ‘working excessive hours, while admirable, raises serious questions when it jeopardises job performance, particularly when critical management decisions are at stake’. Bear in mind that when official investigations search for the causes of disasters they instinctively focus on tangible, physical causes like rubber O-rings and air temperatures; intangible human factors like fatigue are seldom in the forefronts of investigators’ minds.
Lack of sleep has contributed to, if not caused, a string of disasters and near disasters in nuclear power plants. Many of them occurred in the early hours of the morning – a common feature of sleep-related accidents – and stemmed from failures by human operators to make sensible decisions when faced with the relevant information. Research has confirmed that nuclear power-plant operators who work night shifts experience real problems with sleepiness, distractibility and poor alertness. Even if they are not particularly sleep-deprived, they are unlikely to perform well in the early hours of the morning. And that is when the accidents happen.
The worst nuclear incident so far in the USA took place in March 1979, when the reactor at the Three Mile Island power station near Harrisburg in Pennsylvania came close to meltdown. The near-disaster at Three Mile Island arose in the early hours of the morning, after operators failed to recognise what their instruments were plainly telling them – namely, that an automatic valve had closed, cutting off the water supply to the coolant system. The reactor shut itself down automatically, as it was designed to do when a malfunction like that occurred. But a series of errors by the human operators led to a dangerous loss of coolant from the reactor core and almost turned an incident into a catastrophe. Radioactive gases were released from the partially exposed reactor core, but the containment vessel fortunately prevented them from escaping into the environment. Although no one died as a direct result of the Three Mile Island accident, it had a massive impact on the American nuclear industry. The damaged reactor took ten years to decontaminate and remained unusable. Fatigue is believed to have contributed to the operators’ repeated failures to handle the incident correctly.
The worst nuclear accident thus far in history occurred at the Chernobyl nuclear power station in April 1986. It too was sleep-related, and started in the early hours of the morning when the operators were at their lowest ebb. The disaster happened when the engineers operating one of the station’s four nuclear reactors made a series of irrational judgments. They attempted an ill-conceived experiment that involved shutting down the reactor’s regulatory and emergency safety systems and withdrawing most of the control rods from the core, while allowing the reactor to continue running. The operators exhibited the alarming propensity to take inappropriate risks that is characteristic of tired people. As a later report put it, they behaved ‘like intelligent idiots’.
The reckless behaviour of Chernobyl’s operators caused a chain reaction. At 1:23 a.m. on the morning of 26 April a series of explosions blew the reactor apart. There was a partial meltdown of the reactor’s graphite core and it caught fire. Large amounts of radioactive material were released into the environment – several times the amount created by the atom bombs dropped on Japan in World War Two. Some of it was carried by winds and contaminated several western European countries, including France and the UK. Thirty-two people at the Chernobyl plant died at the time of the accident and several more died soon after from severe radiation exposure. The long-term damage to the health of populations living in affected areas remains a matter of controversy, but it is undoubtedly huge. Several thousand people have died, or will die, as a result.
Over and over again, man-made disasters like Chernobyl and Exxon Valdez have occurred at night or in the early hours of the morning, when people’s reactions and judgment are at their weakest. We saw earlier that drivers are much more likely to have a serious crash late at night than in the middle of the morning. Almost everyone who works night shifts displays signs of sleepiness and impaired performance, and it is not difficult to see why. Working at night forces people to perform at a time when their biological clocks are telling them to sleep, and to sleep when their biological clocks are telling them they should be awake. They perform worse when they are at work, and they are less able to sleep when they go home, as a result of which they become tired and accident-prone. Add chronic sleep deprivation to the brew and you have a potentially lethal concoction. And we all have to live with the consequences.
The price of eternal vigilance is liberty (#ulink_2e1871fd-95d6-5a4a-840f-c5b271f36faa)
Care is heavy, therefore sleep you.
Thomas Dekker, Patient Grissil (1603)
If society were to recognise the true importance of sleep, then attitudes towards tiredness on the roads and in the workplace might become more enlightened. In a more sleep-conscious world it would no longer be socially acceptable, let alone admirable, for people to drive or turn up for work suffering from severe fatigue, any more than it is now acceptable to be drunk in the workplace or behind the wheel of a car. Napping during working hours would be tolerated and even encouraged, rather than stigmatised as a sign of sloth, drunkenness or illness. Meanwhile, society continues to turn a blind eye to people driving cars, flying aeroplanes, practising medicine, operating safety-critical machinery and running nations when they are mentally and physically impaired by lack of sleep.
In the next chapter we shall see that sleep-deprived people are bad at making decisions and communicating those decisions to others. Their judgment is impaired, they are easily distracted, they respond poorly to unexpected information, they lack flexibility, they persist with inappropriate solutions to problems and they are prone to taking foolish risks. These are not the characteristics any of us would wish to see in the people who make life-and-death decisions in the corridors of power, hospitals, flight decks or nuclear power stations.
3 Dead Tired (#ulink_d0cf0e7a-1da5-5fa3-893d-dcbfe8fec2a7)
You lack the season of all natures, sleep.
William Shakespeare, Macbeth (1606)
Does it really matter that many people in industrialised countries no longer get enough sleep of sufficient quality at the right times? We have seen one reason: the fact that sleepiness causes accidents. But far more than that, inadequate sleep matters because of what it does to our minds and our bodies each and every day.
Sleep is eloquent in its absence. We know that if we miss a night’s sleep we will feel bad the next day. But the unpleasant sensations of acute fatigue evaporate after a good night’s sleep and we soon forget. Far less obvious are the insidious, cumulative consequences of seldom getting quite enough sleep, night after night, week after week. Chronic sleep deprivation creeps up on us. It has pervasive effects on our mood, social skills and mental abilities – especially judgment, creative thinking and problem solving. It can also impair our physical health and make us more vulnerable to disease, as we shall see in the next chapter. However, the first and most obvious symptom of insufficient sleep is sleepiness, and that is where we shall start.
Sleepiness (#ulink_5308485c-ae0c-57db-bf98-8a1a2a23d417)
Life is one long process of getting tired.
Samuel Butler, Notebooks (1912)
The longer you go without sleep, the sleepier you feel. Objective measurements prove that there is indeed a close relationship between sleep deprivation and sleepiness. That relationship is ‘dose-dependent’, which means that the longer you have been deprived of sleep, the faster you will fall asleep when given the opportunity. Really tired people can fall asleep almost anywhere, as William Shakespeare observed:
Weariness
Can snore upon the flint, when resty sloth
Finds the down pillow hard.
If you are able to lie on a hard floor and go to sleep immediately during the middle of the day, you are probably sleep-deprived. (An obvious point, but no less true for that.)
Sleep will eventually force itself upon you if you go long enough without it. When scientists carry out sleep-deprivation experiments with human volunteers they often have to work quite hard to keep their subjects awake. Someone who has been deprived of sleep for two or three days requires stimulation, activity and variety to stop them falling asleep, no matter how well motivated they are to stay awake. Ian Oswald, a British scientist who conducted sleep-deprivation experiments in the 1960s, recalled walking the streets of Edinburgh flanked by exhausted volunteers whom he was working hard to keep awake. Even then, he would often see their eyelids closing as they walked along in a twilight state somewhere between waking and sleep.
Sleepiness and its flip side wakefulness determine how alive you feel and how well you perform every day of your life. But until the late 1970s there was no standard tool for measuring sleepiness. Then Mary Carskadon of Brown University in the USA invented a simple technique called the multiple sleep latency test (MSLT). It measures sleepiness like this. The subject is invited to go into a dark, quiet room in a sleep laboratory, to relax and fall asleep. Sensors detect the physiological signs of sleep (of which more later). As soon as the subject falls asleep, he or she is woken up. The key measurement is the time taken to fall asleep. The purpose of the MSLT is to measure daytime sleepiness, so the tests are generally carried out between ten in the morning and eight in the evening. The procedure is usually repeated four or five times during the course of a day.
The length of time between lying down and falling asleep is called the sleep latency. A daytime sleep latency of 15–25 minutes is generally interpreted as a reassuring sign of normality. Someone who is sleep-deprived will fall asleep faster. A sleep latency of less than ten minutes raises questions; there is a good chance that the person concerned will be experiencing intrusive daytime sleepiness, especially during the normal afternoon dip in wakefulness or when bored. A daytime sleep latency of less than five minutes usually signifies excessive tiredness, implying that the individual is substantially sleep-deprived or suffering from a sleep disorder.
Not everyone who falls asleep quickly in the MSLT is sleep-deprived, however. There are a few healthy people who can fall asleep in a trice, given the opportunity and the will. These individuals have the ability to go out like a light even after they have had unlimited amounts of sleep and without displaying any other signs of sleep deprivation. They just seem to be unusually good at relaxing and going to sleep during the day, regardless of their need for sleep. An unusually short sleep latency should therefore be viewed as strong evidence of sleep deprivation, but not conclusive proof.
The MSLT is conducted in a sleep laboratory, using electronic sensors to determine the onset of sleep objectively. There is, however, a crude, do-it-yourself version of the MSLT. This entails lying on a bed under sleep-friendly conditions – lights off, shoes off, TV off, no noises off, and so on – with one hand dangling over the edge of the bed and holding a metal object such as a spoon. Under the dangling hand rests a plate or some other hard surface. When you fall asleep your muscles relax and the spoon drops onto the plate with a loud clatter. All being well, you should then wake up, check your stopwatch and write down your sleep latency. If, on the other hand, you wake up several hours later to find your spoon lying on the plate, it may be that you are sleep-deprived. An even simpler way of assessing your own subjective sense of sleepiness is with a self-rating method called the Stanford Sleepiness Scale. This is a seven-point scale, ranging from 1 (defined as feeling active, vital, alert, wide awake), through 2 (functioning at a high level, not at peak), 3 (relaxed, not full alertness, responsive), 4 (a little foggy, not at peak, let down), 5 (tired, losing interest, slowed down), and 6 (drowsy, prefer to be lying down), to 7 (almost in a reverie, hard to stay awake).
Sleepiness is affected by many other factors besides the length of time since you last slept. Foremost among these is the time of day. Other things being equal, it is easier to fall asleep at certain times of the day and harder at other times. Wakefulness fluctuates naturally over the 24-hour cycle, with low points occurring in the early hours of the morning and again in the afternoon. This daily rhythm in wakefulness is mirrored by fluctuations in performance, which manifest themselves in many ways. For instance, you are more likely to crash your car or make a mistake when performing a difficult task in the early hours of the morning or in the afternoon. Sleep deprivation amplifies the effects of time of day, so the more sleep-deprived someone becomes, the deeper their daily troughs in wakefulness.
Stimulation and activity can mask sleepiness, at least for a while. Busy people often fail to notice how tired they really are until they relax at the weekend or on holiday. Their true state then becomes apparent. Sleepiness is even influenced to some extent by the nature of your previous activity. Experiments have confirmed, for example, that people feel sleepier and fall asleep more quickly after watching television than after taking a walk.
Fighting the beast (#ulink_5606a271-0a1e-5188-9fbc-1b32ee472e7b)
Thou art inclined to sleep; ’tis a good dullness,
And give it way: I know thou canst not choose.
William Shakespeare, The Tempest (1611)
What does it feel like to be seriously tired? For most of us real exhaustion is thankfully a rare experience. But for some, it is all too real. One of the most graphic accounts ever written about crushing fatigue can be found in the autobiography of the American aviator Charles Lindbergh. In 1927 Lindbergh made the first solo non-stop flight across the Atlantic in his single-engine plane The Spirit of St Louis. It lasted 33.5 hours. In his 1953 Pulitzer Prize-winning autobiography, Lindbergh described how his flight from New York to Paris came close to disaster – not because of mechanical failure or bad weather, but because of simple lack of sleep.
Before his marathon flight Lindbergh was told that it would be impossible for one man to fly an aeroplane alone for 30 or 40 hours without sleep. Lindbergh disagreed: he had worked for more than 40 hours at a time without sleep, so he did not see why he should be incapable of flying for that long sitting down. He was almost proved wrong.
The timing of Lindbergh’s departure remained uncertain until the last moment. It all depended on the weather. When an opportunity suddenly arose to take off the following morning at daybreak, Lindbergh went back to his hotel to cram in a few hours’ sleep. As a professional pilot he had learned from experience that every little bit of sleep helps. Even so, it was close to midnight before he reached his room, leaving barely three hours if he was to be ready to fly at dawn. As he eventually lay down to sleep, Lindbergh regretted the flawed planning that would force him to set off in a state of sleep deprivation. He knew he would have been better off starting his marathon fully rested – not just because that would make him a better pilot, but also because tiredness would prevent him from fully appreciating the experience. Lindbergh wanted to enjoy his flight. Even then, in those precious few hours, his sleep was further eroded when someone woke him to ask a stupid question. By three o’clock that morning Lindbergh was at the airfield preparing to take off. And so began his epic, sleepless flight across the Atlantic.
After only a few hours in the air, Lindbergh felt tiredness creeping up on him. How pleasant it would be, he mused, to doze off for a few seconds. He shook himself. He could not afford to feel like that so early in the trip. Later that day, and still less than nine hours into the flight, fatigue hit him again:
My eyes feel dry and hard as stones. The lids pull down with pounds of weight against their muscles. Keeping them open is like holding arms outstretched without support. After a minute or two of effort, I have to let them close … My mind clicks on and off, as though attached to an electric switch with which some outside force is tampering. I try letting one eyelid close at a time while I prop the other open with my will. But the effort’s too much. Sleep is winning. My whole body argues dully that nothing, nothing life can attain, is quite so desirable as sleep.
If sleepiness weighed so heavily upon him now, how could he get through the night, to say nothing of the dawn and another day and its night and possibly even the dawn after that? Lindbergh was ashamed. How could he let something as trifling as sleep ruin the record-breaking flight he had spent so many months planning? How could he face his sponsors and admit he had failed to reach Paris because he was sleepy? This must be how an exhausted sentry feels, he thought: unable to stay awake, yet knowing he will be shot if he is caught napping. He had no choice but to battle against his fatigue, minute by minute. In the end, it would all come down to sheer will power.
As the first traces of dawn began to appear on the second morning, Lindbergh felt the overwhelming desire to sleep falling over him like a quilt. Dawn was the time he had dreaded most:
Like salt in wounds, the light of day brings back my pains. Every cell of my being is on strike, sulking in protest, claiming that nothing, nothing in the world, could be worth such an effort; that man’s tissue was never made for such abuse. My back is stiff; my shoulders ache; my face burns; my eyes smart. It seems impossible to go on longer. All I want in life is to throw myself down flat, stretch out – and sleep.
Lindbergh searched for some way to stay alert. Shaking his body and stamping his feet no longer did any good. He had no coffee with him, but consoled himself with the thought that he had long since passed the stage when coffee could have helped. He pushed the stick forward and dived down into a ridge of cloud, pulling up sharply again after clipping through its summit. That woke him up a little, but not for long. He was thankful that The Spirit of St Louis had not been designed to be a stable aeroplane. The very instability that made it difficult to fly now guarded him against catastrophic errors. The slightest relaxation of pressure on stick or rudder would start a climbing or a diving turn, hauling him back from the borderland of sleep.
In the twentieth hour sleepiness temporarily gained the upper hand. Lindbergh suddenly awoke to find the plane diving and turning: he had been asleep with his eyes open. The realisation that he had lost control of himself and the plane was like an electric shock, and within seconds he was back in command. But as time passed, and no new emergencies occurred, he lapsed back into a dreamlike state, unsure whether he was dreaming through life or living through a dream. Over and over again he fell asleep with his eyes open, knowing he was falling asleep and unable to prevent it. Extreme measures were needed. He struck his face sharply with his hand, but felt hardly any sensation. He hit his face again, this time with all his strength. All he felt was numbness. Not even pain would come to his rescue. He broke open a capsule of ammonia and inhaled, but smelt nothing. Lindbergh realised how deadened his senses had become.
After 24 hours in the air and with more than a thousand miles still to go, Lindbergh seriously doubted whether he could stay awake long enough to avoid crashing into the Atlantic. But just as he felt death and failure staring him in the face, he began to turn the corner. The seriousness of his crisis had at last broken the spell of sleep and summoned up his last reserves of mental strength. He felt as though he was recuperating from a severe illness. And, as the history books relate, Charles A. Lindbergh made it to Paris and became an international hero. His remarkable last-minute rally was almost certainly a reflection of his circadian rhythm. His next peak of alertness came just in time. If his flight had continued much longer, he would inevitably have plunged back down into another circadian trough of fatigue from which he might never have ascended.
Lack of sleep has always been one of the least glamorous aspects of life at sea. In 1938 the 18-year-old Eric Newby signed on as an apprentice aboard one of the last square-rigger sailing ships. Newby’s autobiographical account of his voyage, The Last Grain Race, charts his experiences as he made the round trip from Belfast to Australia and back again via Cape Horn. The ship had a minimal crew, so each man worked hard and slept little. ‘I had never been so tired in my whole life,’ wrote Newby, ‘far too exhausted to appreciate the beautiful pyramids of sail towering above me.’ After coming off watch he would fall into a dreamless sleep, so deep that when he awoke and went up on deck again he felt like a sleepwalker. On the return voyage his ship was hit by an awe-inspiring storm that soon had the crew’s compartment awash in six inches of water. But the sailors who were not on duty snored through it all, so great was their appetite for sleep. Like soldiers preparing for the next battle, they lay ‘absorbing sleep greedily like medicine’.
The writer C. S. Forester charted the sleepiness of the long-distance mariner in his Hornblower novels, which relate the fictional Royal Navy career and Napoleonic War adventures of Horatio Hornblower, a character partly modelled on Admiral Horatio Nelson. In one story, the gallant Hornblower is exhausted from lack of sleep after a daring escape from France and a prolonged battle with pursuing enemy ships. Like Charles Lindbergh, Hornblower experiences the disturbing sensation that his mind has become disconnected from his body:
His voice sounded strange and distant in his own ears, like that of a stranger speaking from another room, as he issued his orders; the very hands with which he held the ropes seemed not to belong to him. It was as if there was a cleavage between the brain with which he was trying to think and the body which condescended to obey him.
Sleep deprivation was a fact of life for Hornblower’s real-life counterpart as well. When Horatio Nelson was commanding a Royal Navy warship he seldom had more than two hours of uninterrupted sleep and sometimes stayed on deck all night. However, like many leaders famed for coping with little sleep, Nelson had a well-developed ability to take catnaps during the day. He would nap in his cabin in a black leather armchair, his feet up on a chair. As we shall see later, a faculty for napping has enabled many high achievers to cope with meagre rations of night-time sleep.
Even in the twenty-first century, napping is a crucial skill for sailors – especially when sailing single-handed. In February 2001 the British yachtswoman Ellen MacArthur crossed the finishing line of the Vendée Globe boat race after 94 days alone at sea. She had travelled 24,000 miles across three oceans to become the fastest woman to sail single-handedly around the globe. For 13 weeks she had managed her 18-metre yacht in some of the world’s roughest seas by herself. The only way Ellen MacArthur could survive was to become a past master of napping, and divide her sleep into multiple brief naps. During the 94-day voyage she took 891 naps, each lasting on average 36 minutes, giving her a total of about five and a half hours of sleep a day. Even sleeping in such short bursts, MacArthur frequently had to rely on what she called her ‘sixth sense’ to wake her when something urgently required her attention.
A soil for peevishness (#ulink_31da901f-b36f-5d30-93c2-10b97a1ef0e7)
He that sleeps feels not the toothache.
William Shakespeare, Cymbeline (1609–10)
Lack of sleep does far more than just make us feel sleepy, however: its tentacles reach out and twist our emotional, cognitive and physical states. One of the first casualties is mood. Tired people are emotionally less resilient and more prone to irritation or sadness. Tiredness also impairs our social and emotional skills, with potentially damaging consequences for personal relationships. A tired person can be physically present but psychologically and emotionally absent. In The Screw-tape Letters, C. S. Lewis imagines an experienced devil instructing his neophyte nephew on how to corrupt a young human. The best way, he advises, is through fatigue:
The paradoxical thing is that moderate fatigue is a better soil for peevishness than absolute exhaustion … It is not fatigue simply as such that produces the anger, but unexpected demands on a man already tired.
After a night without sleep, healthy people exhibit clear disturbances in mood, which are characterised by irritability, tension and reduced vigour. These symptoms normally evaporate after a good night’s slumber. Sleep-deprived people, like drunks, lose their social inhibitions and behave in inappropriate ways; they are prone to outbursts of childish humour, which others around them do not always find hilarious. (And strangely, for reasons that remain unclear, acute sleep deprivation can also have the counterintuitive effect of stimulating the libido.)
Severe sleep deprivation can induce feelings of persecution and mild paranoia. It is well known among sleep scientists that the volunteers who take part in their sleep-deprivation experiments often become irritable and impatient. Some subjects become slightly paranoid, convinced that the researchers and fellow volunteers are plotting against them. In rare instances, exhaustion can provoke more dramatic changes. In one documented case, a previously healthy man became psychotic after four nights of badly disrupted sleep and believed he was the Messiah.
Chronic sleep deprivation – that state of never getting quite enough sleep, day in day out, over a prolonged period – is far more common in everyday life than the acute deprivation that comes from having no sleep at all for one or two nights. And chronic sleep deprivation can have just as much cumulative impact, leaving even the saintliest person with a shorter fuse. The writer John Seabrook described the debilitating fatigue that goes with having a small baby like this:
The burning eyes; the band of fatigue that tightens around the skull, a sensation some liken to the feeling that you’re always wearing a hat; the irritation – at each other, at friends, at the cat’s water bowl, which I kept kicking by accident …
Lack of sleep and tiredness are obviously not wholly responsible for the tetchiness, aggression and petty violence of everyday life, but it is a racing certainty that they contribute towards making the world a nastier place. Conversely, there is little doubt that good sleep makes us feel better. In one study, researchers issued volunteers with pocket computers on which they logged their sleep patterns, moods and social interactions over a two-week period. The results showed that going to sleep earlier in the evening was consistently associated with better mood and better social interactions the following day.
Tired people are stupid and reckless (#ulink_bbd9505f-01f8-5e16-b9e2-966c10e0ea01)
Fatigue makes women talk more and men talk less.
C. S. Lewis, The Screwtape Letters (1942)
Besides making us grumpy and poor company, sleep deprivation impairs our mental abilities in many subtle and not-so-subtle ways. In brief, tired people are stupid and reckless. Sleep deprivation damages our ability to perform tasks that require attention, thought, judgment, memory, social skills or communication skills – which covers the ground fairly comprehensively. Tired people also seem to lose sight of the consequences of their actions, liberating them to do silly and sometimes catastrophic things: the Chernobyl and Exxon Valdez disasters were just two examples.
Even modest sleep loss will measurably reduce your mental performance. After one night without sleep, you will have slower reactions, make more mistakes and find it harder to maintain attention. Unsurprisingly, two or three days of sleep deprivation produce even bigger impairments. Young adults are no more resistant than older people. If anything, they are more vulnerable. When researchers compared the consequences of one night of total sleep deprivation on healthy 80-year-olds and 20-year-olds, they recorded larger disturbances in the mood and cognitive performance of the younger subjects.
Reducing someone’s sleep for several nights in a row can undermine their performance just as much as completely depriving them of sleep for one or two nights. When scientists limited healthy young adults to an average of only five hours’ sleep a night for a week, the subjects became progressively sleepier and their performance deteriorated significantly. Two full nights of catch-up sleep (equivalent to a restful weekend) were needed to reverse the decline.
The armed forces have understandably maintained a long-standing interest in how well people hold up when they are deprived of sleep, as often happens in conflict. Experience shows that soldiers can continue to perform reasonably well after days of sleep deprivation under combat conditions, buoyed up by adrenaline, physical exertion and strong motivation. With sufficient stimulation and will power, military personnel can usually keep going without sleep for three or four days before they keel over. In one study, for example, men were assessed throughout a strenuous combat training course lasting several days. Some of the trainees were allowed no sleep at all, while others were permitted a few hours in the middle of the course. All the men displayed a substantial deterioration on measures of mood, vigilance and reaction time, with those who got no sleep performing even worse than those who got some. By the end, the trainees who had not slept at all were suffering from clinical symptoms including sensory disturbances.
Sleep-deprived people can often perform certain tasks reasonably well in short bursts, despite their fatigue. The real problems arise if they have to sustain their effort for any length of time. This lack of staying power was highlighted by experiments conducted in the 1950s at the Walter Reed Army Institute of Research in the USA. Sleep-deprived volunteers scored well in tests of reaction times when they were only required to react a few times over a period of one minute. But when they had to make lots of rapid responses spread irregularly over a period of 15 minutes, their performance fell apart. Sometimes they reacted quickly and sometimes they reacted very slowly or not at all. The more sleep-deprived they were, the more their responses varied. That experiment illustrates a general pattern that has emerged from studies of sleep deprivation – namely, that the performance of tired people becomes much more variable and inconsistent. Their accuracy and speed can fluctuate wildly over periods of a few minutes. In one study, for example, scientists monitored the performance of volunteers throughout an 88-hour period of total sleep deprivation. The subjects’ performance on a task requiring vigilance and coordination was much more variable (as well as just plain worse) than a comparison group, and the longer they went without sleep the more variable their performance became. These wild fluctuations in performance probably arose because their attention was repeatedly blotted out by microsleeps. As we saw earlier, someone who is very tired can lurch from wakefulness to sleep and back again in a matter of seconds without even noticing.
Much of the research on sleep deprivation has focused on how it impairs people’s ability to perform tasks requiring rapid but relatively simple decisions, involving very basic skills such as the ability to maintain attention under monotonous conditions. These skills are sensitive to sleep deprivation (which is partly why they have been so frequently measured) but they also have only a tenuous bearing on what happens in reality. The sorts of judgments and decisions we all have to make in real life usually demand far more than just the ability to stay awake and press buttons. Real decisions require us to assimilate and process complex, incomplete and often contradictory information, to keep track of our actions, assign priorities, ignore distractions and communicate with other people. The truly frightening aspect of sleep deprivation is the way it erodes all of these capacities.
Sleep-deprived people are bad at making complex decisions that require them to revise their plans in the light of unexpected news, to ignore irrelevant information and to communicate effectively. These are precisely the capabilities that we all need most when dealing with the vagaries of normal life – as do politicians, managers, doctors, military commanders and other key decision makers.
Even a single night without sleep will impair your ability to think flexibly and creatively. Sleep-deprived people perform badly on all aspects of creative thinking, including originality, flexibility, generating unusual ideas, being able to change strategy, word fluency and nonverbal planning. Tired people tend to persist with their current activity regardless of whether it is appropriate – a characteristic that psychologists call perseveration. In one cleverly revealing experiment, sleep-deprived volunteers played a realistic marketing game that required them to make complex decisions and then continually update those decisions in the light of new information. After 36 hours without sleep, the well-motivated subjects were still able to read and absorb written information. But their ability to make sound decisions based on that information deteriorated markedly. As they became more sleep-deprived they found it increasingly difficult to recognise when to change tactics in light of changed circumstances. Their thinking became rigid and they tended to persist with incorrect responses. Eventually, after 36 hours without sleep (the equivalent of losing just one night’s sleep) their ability to play the game collapsed.
Sleep-deprived people reveal their blunted creativity and mental inflexibility through alterations in their spoken language. After 36 hours of sustained wakefulness, people display a marked deterioration in verbal fluency and inventiveness. They are more reliant on routine responses and tend to become fixated with a particular category of words. They also start using inappropriate, monotonous or flattened intonation when reading out loud. Think about how people talk when they are drunk and you will get the picture. Tired people are bad at finding the right words. Their language becomes less spontaneous and expressive, and they are less willing to volunteer information that others might need to know. All in all, they are worse at communicating their thoughts, feelings, decisions and actions. Being a poor communicator is unhelpful, whether you are a head of state trying to deal with a crisis or simply someone who values their social life.
The supposedly robust adolescent is, if anything, even more vulnerable than older people. One study found that when youths aged 10–14 years were restricted to only five hours in bed for one night, their verbal creativity, verbal fluency and ability to learn new abstract concepts were all impaired. Less complex mental functions, such as rote learning, were unaffected by this modest degree of sleep restriction. So the sleep-deprived adolescent would still be able to go through the basic motions at school the next day, but would be unable to perform to anything like their true potential. And it is not entirely unknown for adolescents to go to school after getting less than a full night’s sleep.
As well as sapping our ability to perform, sleep deprivation also impairs our motivation. Tired people just can’t be bothered. In one experiment, researchers persuaded a group of male students to work continuously for 20 hours without sleep and then observed them in various social settings. Sleep deprivation diminished everyone’s performance, but the students who were working in groups performed even worse than those who were working individually. This was because working in a group gave them the opportunity to loaf – and they did.
Another alarming characteristic of sleep-deprived people, and something else they have in common with drunks, is their propensity to take risks. Experiments have shown that as people become more fatigued, they are more attracted by actions that might bring big rewards and less worried by the possible negative consequences of those actions. For instance, French scientists assessed the risk-taking propensities of military pilots who were involved in a maritime counter-terrorism exercise. This required them to make strenuous night flights, depriving them of sleep. The data showed that as the exercise progressed, the pilots became more impulsive. In effect, sleep-deprived people become more reckless and foolhardy. This is yet another characteristic that you would not wish to encounter in someone who is in charge of a hospital ward or a political crisis or a nuclear power station, or the family car for that matter.
Alcohol, beauty and old age (#ulink_8d776144-d30e-54b5-947b-b8ff5d5a1bc6)
It provokes the desire, but it takes away the performance.
William Shakespeare, Macbeth (1606)
Tired people resemble drunk people in several respects. Most obviously, tiredness and alcohol both hamper our ability to perform tasks that require judgment, attention, quick reactions and coordination – such as driving a car, for example. Missing a night’s sleep has an impact on driving skills comparable to drinking a substantial amount of alcohol. In both cases safe driving is no longer possible; in one case, however, it is both legal and socially acceptable.
To compare the effects of sleep deprivation and alcohol, researchers persuaded healthy young men to drive a simulator while under the influence of varying degrees of sleepiness and with varying blood-alcohol levels of up to 0.08 per cent. (For comparison, the legal limit for driving in most countries is 0.08 per cent blood alcohol and in Scandinavian countries it is 0.05 per cent.) Alcohol undermined their ability to maintain a suitable speed and road position, and so did sleep deprivation. Drivers who had been awake for 21 hours (hardly a remarkable feat) performed as badly as drivers with a blood-alcohol level of 0.08 per cent. So, next time you miss a night’s sleep, try to remember (if you can) that your driving ability will be as bad as if you had a blood-alcohol level that would be illegal in most countries.
Recent research has underlined the parallel between tiredness and alcohol. Scientists assessed volunteers driving on a closed course, both after drinking alcohol and after sleep deprivation. Detailed comparisons showed that both acute sleep deprivation (one night with no sleep) and chronic sleep deprivation (two hours less sleep than normal each night for a week) caused impairments in performance and reactions that were almost indistinguishable from those caused by illegally high blood-alcohol levels. The inescapable conclusion is that even relatively modest sleep deprivation, of the sort that many people experience in everyday life, has potentially dangerous consequences. Shaving a couple of hours off your sleep each night for a week can make you as incapable behind the wheel as a drunk driver.
Another striking similarity between sleep deprivation and alcohol is that as well as impairing our performance, sleep deprivation also undermines our ability to realise that our performance has been impaired, as we shall shortly see. (Try saying that sentence quickly when you are tired or drunk.) Tired people, like drunk people, have a misplaced confidence in their own abilities. This dangerous trait was highlighted in an experiment in which students took cognitive tests after they had been deprived of sleep for 24 hours. Predictably, they performed worse than subjects who had slept well the night before. However, when asked to assess their own performance, the sleep-deprived subjects awarded themselves higher ratings than did the non-deprived subjects. Tiredness had marred their ability to appreciate their own inability.
Cultural attitudes towards being tired or drunk behind the wheel of a car are very different, despite the fact that the net outcomes are remarkably similar and sometimes fatal. Driving when drunk is illegal and (nowadays) socially unacceptable, whereas driving when tired is neither. People still boast about their feats of sleep-deprived driving, in the way that people once boasted of their ability to drive after downing stupefying quantities of booze. Of course, one big difference between drinking alcohol and going without sleep is that drinking alcohol is enjoyable. Sleep deprivation has only the bad bits to offer, including the hangover.
Being tired and drinking alcohol are obviously not mutually exclusive. Indeed, the two often go hand in hand. A night on the town is often a night of little sleep. What is more, they reinforce each other. Tiredness amplifies the effects of alcohol and vice versa. It is a common experience (except presumably among lifelong teetotallers) that alcohol packs a heftier punch when we are tired – say, at the end of a hectic working week. Even moderate amounts of alcohol produce a big sedative effect after insufficient sleep. Conversely, the effects of alcohol are somewhat blunted if you are well rested. Experiments have found that alcohol reduces the alertness of people who have had less than eight hours’ sleep the previous night, whereas the same amount of alcohol makes no difference if they have had unlimited sleep. If you want to enjoy a few drinks without wilting, make sure you sleep properly the night before.
Another common experience is that the effects of alcohol vary according to the time of day when it is drunk. This happens because alcohol reinforces our natural circadian rhythm in sleepiness, exaggerating the troughs in alertness that normally occur in the early hours of the morning and again in the afternoon. Alcohol consumed at lunchtime or in the early afternoon therefore tends to have a bigger impact than the same amount consumed in the early evening, when alertness is normally higher. Lunchtime boozing really is more likely to make you fall asleep at your desk or crash your car than those pre-dinner ‘sharpeners’.
Scientists have also uncovered some intriguing parallels between sleep deprivation and the normal ageing process. As we grow older, our performance declines on many psychological and neurological measures. A similar pattern of deterioration is observed in young people after sleep deprivation. One experiment found that after 36 hours without sleep, adults in their twenties had a performance profile similar to that of non-sleep-deprived people aged about 60. So, if you are in your twenties and you want to know how it feels to have the brain of a healthy 60-year-old, just stay up all night. Then you will know. The reason why ageing and sleep deprivation exert similar effects may be because they both impair the functioning of the prefrontal cortex, a region of your brain that is extremely active when you are awake.
To complete the three-way permutation, alcohol and old age make an unpleasant cocktail. Being old is generally bad for sleep, and so is being an alcoholic. Being old and alcoholic is even worse. The elderly are more prone to insomnia, as we shall see in a later chapter. Alcoholism is also accompanied by sleep problems. And when old age and alcoholism combine within the same person they reinforce their malign influences on sleep. Researchers have found that older alcoholics have significantly worse sleep problems than younger alcoholics.
Sleep, or lack of it, can also affect physical appearance – a belief encapsulated in the term ‘beauty sleep’. Although sleeping all hours will not necessarily make you more beautiful, prolonged lack of sleep will detract from your physical charms. Animals that have been experimentally deprived of sleep for long periods develop unsightly skin disorders. Lack of sleep in humans, especially adolescents and young adults, might exacerbate skin problems such as acne. Sleep deprivation weakens the ability of the skin to maintain its normal protective functions as a barrier against dirt and microbes. That said, the scientific evidence for a direct causal link between sleep and an unblemished complexion remains sparse, Sleeping Beauty notwithstanding.
Lack of sleep probably does contribute to the depressing tendency of men to become pot-bellied and flabby in middle age. In men (but not women) almost the entire day’s production of growth hormone within the body occurs during sleep. The less sleep a man gets, the less growth hormone his body produces. As part of the normal ageing process, the total amount of sleep and the production of growth hormone both decline in parallel. Scientists have suggested that this age-related fall in growth-hormone production could be responsible for the systematic replacement of muscle by flab, better known as middle-aged spread. If so, dwindling sleep might be an important ingredient in the expanding waistline, double chins and spindly legs that help to make male middle age such a joy.
Champion wakers (#ulink_e5fc89c1-0fd4-554b-af1b-e1faafe93630)
I’ll wake mine eyeballs out.
William Shakespeare, Cymbeline (1609–10)
What happens to people if they get no sleep at all for a long time? One of the first scientific experiments on sleep deprivation dates from 1896, when Professor G. T. W. Patrick and his colleague Dr Allen Gilbert of the Iowa University Psychological Laboratory kept three volunteers awake for 90 hours. Patrick and Gilbert charted the now classic signs of prolonged sleep deprivation, including progressive deteriorations in reactions, memory and sensory acuity, together with a decline in body temperature.
Their first experimental subject, an assistant professor at the university, suffered his worst fatigue during the second night. Like Charles Lindbergh, he found that dawn was the cruellest time. He experienced visual hallucinations in which the air seemed full of red, purple and black dancing particles like gnats. All three subjects gained weight during the experiment, but their muscular strength diminished as they became more fatigued. The most noticeable effects were on mental performance: their memory became highly defective and they lost their ability to pay attention. One subject failed to memorise in 20 minutes material that he would normally have committed to memory in two minutes. In all cases, the symptoms disappeared after the experiment.
The first person to become internationally famous for self-imposed sleep deprivation was an American disc jockey called Peter Tripp, whose other claim to fame was inventing the Top 40. In 1959, Tripp managed the feat of staying awake under supervision for more than eight days and nights, a total of 201 hours. He did it to raise money for charity. Tripp even managed to broadcast live during his marathon, from a booth in Times Square, New York.
Peter Tripp suffered. As time went on, his friends and invigilators found it harder and harder to keep him awake. Constant vigilance was required to prevent him from lapsing into microsleeps. Three days into the experiment, Tripp became abusive and unpleasant. After the fifth day he progressively lost his grip on reality and started to experience visual and auditory hallucinations. His dreams broke through into his waking thoughts and he began seeing spiders in his shoes. He became paranoid and thought people were drugging his food. At one point he ran into the street and was nearly knocked down. These disturbing psychological symptoms were accompanied by physical changes, including a continuous decline in body temperature. By the last evening, Tripp’s brain-wave patterns were virtually indistinguishable from those of a sleeping person, even though he was apparently still awake.
After 201 hours of continuous wakefulness Tripp had broken the record and halted the experiment. He immediately fell into a deep sleep that lasted 24 hours. When he finally did awake, his hallucinations had gone and he felt relatively normal. But something seemed to have changed within him. Those close to Peter Tripp felt his personality had altered permanently, and for the worse. His wife left him, Tripp lost his job and he became a drifter. Tripp’s marathon of sleep deprivation certainly did him no good, but it was probably not the sole cause of his subsequent decline and fall. Tripp was taking large doses of Ritalin, an amphetamine-like stimulant drug, to keep himself awake during the marathon, and it is possible that the drug, combined with the sleep deprivation, helped to stimulate his paranoid delusions and hallucinations.
A few years later, Tripp’s record was broken by a 17-year-old high-school student from San Diego called Randy Gardner. In 1965 Gardner stayed awake for 264 hours (or 11 days) in a successful attempt to break into The Guinness Book of Records. Scientists from Stanford University monitored most of his marathon. During the first two days Gardner’s friends helped keep him awake and he did not use caffeine or other stimulants. By the end of the second day he was suffering from blurred vision, making it difficult for him to read or watch TV. By the third day he was irritable and wanted to be left on his own. His speech became slurred and his movements uncoordinated. On the fourth day he experienced memory lapses and mild hallucinations. After nine days without sleep he was unable to complete sentences and had lost the ability to concentrate. On the eleventh and final evening he had double vision.
Despite these temporary but unpleasant symptoms, Randy Gardner suffered remarkably few ill effects. Having stayed awake for 11 days and nights, he went to bed and slept for nearly 15 hours. When he awoke he felt fine. The following night he slept only slightly longer than usual, and within a few days his sleep had returned to normal. He did not go mad and, except for mild hallucinations, he never displayed any psychotic symptoms during the experiment. The experiences of Randy Gardner and others have demonstrated that going without sleep for several days does not generally result in mental illness or other long-term damage.
Some feats of self-imposed sleep deprivation have been endured for purely financial reasons, with not a single scientist in sight. In the depression-era USA of the 1920s and 1930s, a bizarre fad developed for dance marathons, in which people would compete for money. The rules were simple: keep dancing until you drop. This grisly social phenomenon was portrayed in the 1969 film They Shoot Horses, Don’t They? The dance-marathon competitors were supposed not to sleep, although some competitions permitted one dancer to sleep provided their partner held them upright and both kept moving. They must have slept while dancing, since it was not uncommon for these nightmarish marathons to last for weeks. The world record was set by a couple in Chicago, who danced from 29 August 1930 until 1 April 1931 – a total of almost 215 days. The rules allowed them to close their eyes for no more than 15 seconds at a time, so they must have been adept at sleeping with their eyes open. Their reward for this outlandish spectacle of public torture was a paltry $2,000. These dance marathons were eventually made illegal. And talking of torture, let us turn to that uncomfortable subject.
Uses and abuses (#ulink_0b8fe922-fa98-5f44-9299-cafadeada523)
It was always at night – the arrests invariably happened at night. The sudden jerk out of sleep, the rough hand shaking your shoulder, the lights glaring in your eyes, the ring of hard faces round the bed. In the vast majority of cases there was no trial, no report of the arrest. People simply disappeared, always during the night.
George Orwell, Nineteen Eighty-Four (1949)
Sleep deprivation is unpleasant and debilitating. Someone who has not slept for two or three days can feel as if they are losing their mind. That is why, throughout history, sleep deprivation has been exploited as a form of torture and coercion. Fatigue can bring people to their knees, both metaphorically and literally, without leaving a mark on them. It can even be fatal.
According to legend, King Perseus of Macedonia was put to death by being prevented from sleeping when held prisoner in Rome. Sleep deprivation is also said to have been a form of capital punishment in China in times past. The American writer and insomniac Bill Hayes cites a nineteenth-century account of a Chinese merchant who was sentenced to death for murdering his wife. Sleep deprivation was deliberately chosen as the method of execution, on the grounds that it would cause the maximum amount of suffering and would therefore serve as the greatest deterrent to other potential murderers. According to the account, which was written by an American physician, the prisoner eventually died on the nineteenth day, having suffered appalling torment.
Sleep deprivation has been employed for many centuries to soften up prisoners and make them talk. And it still is. Amnesty International found that more than half the torture victims they interviewed had been deprived of sleep for at least 24 hours. The secret police notoriously prefer to make their arrests in the small hours of the morningbecause that is when people are at their weakest and most confused.
When applied patiently and systematically, sleep deprivation is said to be the single most effective form of coercion. The victim is repeatedly woken at odd hours, allowing them little or no sleep. The pattern of awakenings is randomised, so the victim loses all control over when they sleep (an extreme version of what happens to parents of small babies). This unpredictability makes it impossible for the body’s internal clocks to readjust. The circadian rhythms become disrupted, leaving the victim fatigued and in a state akin to severe jet lag. All sense of time and place depart. Even the strongest person can be reduced in this way to a state of helpless and tearful disorientation.
Exhausted people are very poor at making sound judgments based on complex information, including information derived from their own knowledge, beliefs and experience. Sleep-deprived prisoners are therefore much more susceptible to persuasion that their actions or beliefs are wrong. Herein lies the secret of ‘brainwashing’.
In the Korean War of 1950–53, the Communists tortured American and Allied prisoners of war by systematically depriving them of sleep. A constant succession of guards would interrogate a prisoner at random times throughout the day and night, subjecting him to a constant barrage of questions and arguments. The effects on prisoners’ behaviour and beliefs were often profound. Sixty per cent of the US airmen who were captured in the Korean War either confessed to imaginary crimes, such as using biological weapons, or collaborated with the enemy in condemning the USA. When the prisoners were eventually returned to the USA, the US government appointed a panel of experts to discover what had happened. The assumption at the time was that the Communists must have subjected the Allied prisoners to some mysterious and sophisticated form of mind control. Either that, or the men must be traitors and cowards. But the evidence uncovered by the review panel ruled out drugs, hypnosis or other forms of novel trickery. The truth was more prosaic. Just one device had been used to confuse and torment the prisoners until they were ready to confess to anything. That device was prolonged sleep deprivation. A combination of fatigue, confusion, fear and loss of control had produced profound changes in the men.
The practice of sleep-depriving military prisoners continues to this day. In April 2001 a US military surveillance aircraft collided in midair with a Chinese fighter. The American plane was forced to make an emergency landing in China. Meanwhile, the Chinese plane crashed, killing the pilot. The Chinese authorities were not happy: they impounded the American plane along with its crew of 24, sparking a diplomatic row between the two nations. The crew were eventually released after being detained and questioned for 11 days. They later revealed that the Chinese had used sleep deprivation as part of the interrogation process. The American pilot reported that the Chinese had questioned him for several hours on the first night, and thereafter had repeatedly woken him at various times of the night and day, forcing him to snatch a little sleep whenever he could.
Prolonged sleep deprivation lay behind many of the psychiatric casualties of World War One. Thousands of men had to be withdrawn from the horrific conditions of the front line with what was referred to then as shell shock. (Nowadays we would call it post-traumatic stress disorder.) Continuous shelling was undoubtedly a cause of severe stress. For hours or days at a time, men crouched defenceless in muddy trenches, constantly exposed to the threat of instant death or injury but powerless to do anything about it. Even the hardiest of minds could crack. But the shelling broke men for another reason as well: it prevented them from sleeping. Doctors often found that when a man with disabling shell shock was granted respite from the front line, he would rapidly recover and be able to return to his unit within days. Getting a few nights’ sleep in the hospital probably did more good than the psychotherapy that went with it.
When we starve ourselves of sleep in the name of work or play, we go partway down a path that leads eventually to something horrific.
4 The Golden Chain (#ulink_81a2ff50-c972-55a6-b9fe-5b3aa2d2ff90)
Sleep is that golden chain that ties health and our bodies together.
Thomas Dekker, The Guls Horn Book (1609)
We have seen some of the bad things that sleep deprivation does to our minds. What does it do to our bodies? Sleep and physical health are intimately intertwined, which means that inadequate sleep can cause all sorts of physical problems. When sleep deprivation is taken to the extreme, death ensues. Some scientists have argued that many of us neglect or mismanage our sleep to the extent that it damages our health, and that large numbers of people around the world die prematurely every year because of undiagnosed and untreated sleep disorders.
What, then, is the scientific evidence that sleep impinges on our physical health? Some (admittedly crude) indicators point towards a link between poor sleep and poor physical health. For instance, people who are sleepy during the day are more likely to use healthcare. And older people who complain of poor sleep are at greater risk of a heart attack. One American study that tracked thousands of elderly people discovered that individuals with sleep problems were more likely to suffer a heart attack over the following three years.
Lack of sleep and the resulting daytime tiredness are associated with greater sickness absence from work. An investigation of absenteeism among French employees found that those who reported feeling very sleepy at least three days a week were more than twice as likely to take sick leave as their less sleepy colleagues. Sleep problems are also predictive of long-term work disability. Norwegian research found that adults who were experiencing mediocre or poor sleep were more than twice as likely to face long-term work disability a few years later. People who sleep badly also tend to eat badly, which may contribute to their health problems.
Good sleep, on the other hand, fosters mental and physical health. Psychological wellbeing, physical health and longevity are all statistically associated with healthy lifestyle practices, one of which is good sleep. The lifestyle factors associated with a lower risk of dying prematurely include taking physical exercise, not smoking and getting seven or eight hours of sleep a night. For example, recent research that investigated longevity in Japanese people uncovered three important factors, each of which was independently linked with a reduced risk of dying. These factors were walking for at least one hour a day, ikigai (a sense that your life is meaningful), and sleeping for at least seven hours a night. There is even some tentative evidence that people who habitually go to bed early live longer. A study of people aged over 80 found that these long-lived individuals all reported having gone to bed early throughout their lives. However, retrospective evidence of this sort must always be taken with a large pinch of salt. (But not too much salt, because that would be unhealthy.)
At the other extreme, excessive sleep is also linked statistically with poor health – probably because sleeping for unusually long periods is often a sign of illness. Scientists discovered in the 1970s that people whose normal nightly sleep duration was either unusually short (less than four hours) or unusually long (more than nine or ten hours) had a higher than average risk of dying prematurely. Similarly, a study of elderly British people found that those who spent 12 or more hours a day in bed had a significantly higher mortality rate, while those who spent the proverbial eight hours a day in bed had the lowest mortality rate.
Excessively long sleep is often a consequence of heart disease or other medical conditions, so it would be a mistake to generalise this finding very far. There is no reason to suppose, for example, that sleep-deprived teenagers or exhausted adults who lie in bed at the weekends will die younger as a consequence of snatching a few extra hours of rest. Too much sleep can make you feel temporarily below par, however. Experiments have confirmed that healthy people who normally feel refreshed after eight hours of sleep tend to feel groggy and perform badly after they have slept (on request) for 10 or 11 hours. On the other hand, how many healthy adults routinely sleep for 10 or 11 hours at a time? Few of us have any reason to fret about the dangers of sleeping too much.
A waking death (#ulink_ea5ea79a-df58-5457-ae6f-14f5b69f2eaa)
We term sleep a death, and yet it is waking that kills us, and destroys those spirits that are the house of life.
Sir Thomas Browne, Religio Medici (1642)
What happens when sleep deprivation is taken to the extreme? If a slight insufficiency of sleep makes us feel unwell, would a prolonged absence kill us? Setting aside purely anecdotal accounts, science has unsurprisingly not investigated whether forcibly depriving humans of sleep is fatal. Ethical committees would tend to frown upon applications from scientists proposing to test this experimentally. But the evidence from other species is clear. Animals that have been experimentally deprived of sleep for long enough invariably die. There is no reason to suppose that humans are fundamentally different.
Some of the earliest experiments on extreme sleep deprivation were performed in the late nineteenth century by a Russian scientist called Marie de Manacéïne. She deprived puppies of sleep by keeping them constantly active. They all died within four or five days, despite every effort to keep them alive. The younger the puppy, the more rapidly it succumbed. Marie de Manacéïne also noticed a progressive decline in the body temperature of the sleep-deprived animals, a phenomenon that is now known to be a standard symptom of prolonged sleep deprivation in humans and other species. She concluded that sleep was even more crucial for survival than food:
As a rule, the puppy deprived of sleep for three or four days presents a more pitiful appearance than one which has passed ten or fifteen days without food. I can speak from observation, as I was obliged to make experiments on the results of want of food as well as of sleep, and I became firmly convinced that sleep is more necessary to animals endowed with consciousness than even food.
Italian scientists working at the end of the nineteenth century kept adult dogs awake by making them walk. The sleep-deprived dogs all died after 9–17 days, regardless of how much food they ate.
One objection to experiments such as these (apart from the obvious ethical one) is that the scientists had to use increasingly stressful methods to keep the animals awake, so perhaps it was the stress that killed them rather than the sleep deprivation itself. Prolonged stress can impair the immune system and make an animal more vulnerable to infection. However, more recent research has managed to sidestep this methodological problem.
In a long series of experiments, Alan Rechtschaffen and colleagues at the University of Chicago systematically investigated how prolonged sleep deprivation affects rats. They used an experimental procedure known as the disc-over-water method, which works like this. Two rats – the experimental subject and the ‘yoked control’ – are placed on a turntable mounted over a shallow bath of water. The brain-wave patterns of both animals are continuously monitored to detect the onset of sleep. When the experimental rat’s brain waves indicate that it is falling asleep, the turntable automatically revolves slowly, waking the unfortunate rat and forcing it to walk in the opposite direction to avoid being pitched into the water. The control animal, which is on the other side of the turntable and separated by a partition, receives precisely the same treatment at precisely the same times. The crucial difference is that the turntable movements are unaffected by its sleep. The control animal is therefore able to get some sleep when the experimental animal is awake. This cunning technique has the advantage – from the human experimenter’s point of view – of preventing the experimental subject from sleeping without having to subject it to other noxious stimuli.
Rats that are prevented in this way from sleeping invariably die after two or three weeks. The control animals, which experience the same stimuli but not the complete loss of sleep, survive and display relatively few symptoms. Before they die, the sleep-deprived rats all exhibit the same horrible syndrome. This is characterised by a debilitated appearance, skin lesions, increased food intake, weight loss, increased metabolic rate, increased levels of the hormone noradrenaline, and declining body temperature. Some of these changes are symptomatic of excessive heat loss from the body, which has led some scientists to suggest that sleep is crucial, among other things, for the regulation of body temperature.
A progressive rise in metabolic rate (the rate at which the body consumes energy) is an early symptom of sleep deprivation. Sleep-deprived rats eat more to compensate for their rising energy expenditure, but their weight and body temperature nonetheless continue to fall. Feeding them an easily digestible diet helps to slow this process somewhat, but it does not prevent them from dying. An increase in appetite is one of the less obvious effects of sleep deprivation in humans as well. Might it be that chronic sleep deprivation is one of the factors helping to fuel the epidemic of obesity that is currently sweeping the USA, UK and other industrialised nations?
Body and soul (#ulink_056f000a-6d8d-504c-a021-e7d92fc8b9f5)
Health may be as much injured by interrupted and insufficient sleep as by luxurious indulgence.
William Kitchiner, The Art of Invigorating and Prolonging Life (1822)
What of people? Research on humans has stopped short of the lethal sleep deprivation imposed on rats and puppies, but it has delved systematically into the consequences of a few days’ sleep loss. The results consistently show that moderate sleep deprivation has pervasive effects on the human body as well as the human mind. Sleep loss impairs vision, for example, causing blurring and errors in judging distances. It also triggers the familiar decline in body temperature that Marie de Manacéïine observed in her puppies, together with a reduction in blood glucose levels and changes in various hormones.
Set against this, sleep loss has surprisingly little impact on our ability to keep moving around and doing physical work. Moderate sleep deprivation does not greatly diminish our capacity for labour. Physically fit young adults can withstand several days of sleep deprivation without a substantial deterioration in their muscle strength, muscle endurance or cardiovascular responses to exercise. In one experiment, for example, the exercise capacity of young women was assessed following 60 hours without sleep. The sleep deprivation had no significant effect on their aerobic capacity or their endurance for exhausting exercise. In another study, researchers monitored two men while they played a marathon tennis match lasting a week, during which time the players got very little sleep. Although their mental performance deteriorated during the match, the players were able to sustain a high level of physical work. Our muscles can mostly keep going even when our brains are flagging.
Sleep deprivation does disturb many aspects of physiological functioning, however. Breathing is one example. A single night of sleep loss impairs breathing in healthy people, provoking a small but significant reduction in the maximum amount of air that can be exhaled after maximum inhalation. Sleep loss also leads to a substantial blunting of the normal respiratory responses to reduced blood-oxygen levels. After 30 hours without sleep there are marked deteriorations in the strength and endurance of the muscles used for breathing – as revealed, for example, by a reduction in the time for which people can breathe in against a sustained pressure. Such changes could be important in patients with respiratory diseases, who often suffer from chronic sleep loss. Sleep deprivation also slows the rate of cardiovascular recovery from intense exercise. When someone has been deprived of sleep for 24 hours, their breathing rate and oxygen uptake after a burst of intense exercise remain higher for longer.
Sleep loss is accompanied by many changes in body chemistry. People who have been kept awake for more than three days have altered liver functions, marked by large increases in the levels of key liver enzymes, changes in various types of fat and a rise in the amount of phosphorus circulating in the blood. Thyroid hormone levels are affected and biochemical changes can be detected at the level of gene activity.
Glucose metabolism is particularly perturbed by sleep loss. Healthy young men whose sleep was experimentally restricted to four hours a night for six nights became less tolerant to glucose. They took 40 per cent longer than normal to regulate their blood-sugar levels after eating high-carbohydrate food, and their ability to produce insulin fell by nearly a third – a condition resembling the early signs of diabetes. These abnormalities vanished after the men had slept for 12 hours. Fatigue-induced physiological changes like these could contribute to the development of chronic conditions such as diabetes, obesity and high blood pressure, all of which are associated with a shortened lifespan.
Sleep, immunity and health (#ulink_1f2df845-d1fc-5f97-86ab-ea2ec9fcf366)
Our foster-nurse of nature is repose.
William Shakespeare, King Lear (1605–6)
Some of the most interesting, least well understood, and potentially important consequences of sleep deprivation are found within the immune system. In short, lack of sleep can impair the body’s immune defences and thereby make us more susceptible to infection by bacteria, viruses and parasites.
The evidence comes mostly from research with other species. In one experiment, for example, mice that were immunised against the influenza virus were resistant to infection if they were exposed again to the virus a week later. But if the immunised mice were deprived of sleep for seven hours immediately after being exposed to the virus, they were no more resistant to infection than mice that had not been immunised at all. A mere seven hours of sleep deprivation disturbed their immune response enough to erase the benefits of immunisation.
Some scientists have suggested that one reason why prolonged sleep deprivation is ultimately fatal is that it breaks down the animal’s immune defences, making it vulnerable to infection by any opportunistic bacteria and viruses that happen to be in the vicinity. Experiments with rats have shown that following severe sleep deprivation, the lymph nodes and other organs are invaded by potentially dangerous bacteria, which appear to have migrated there from the intestines. However, the role of infection in killing sleep-deprived animals remains a controversial issue.
Sleep loss impairs the human immune system as well. Even modest sleep deprivation evokes measurable changes. One night of sleep loss lowers the activity of natural killer cells and reduces the numbers of several different types of white blood cells circulating in the bloodstream. (Natural killer cells are a special type of lymphocyte, or white blood cell, that attack virus-infected cells and certain types of cancer cells.) Depriving healthy adults of sleep for seven hours on one night suppressed their natural killer-cell activity by 28 per cent. It bounced back to normal after a night of uninterrupted sleep. Moderate sleep loss will also reduce the body’s production of interleukin-2, a chemical messenger substance that plays an important role in regulating immune responses. After two or three days of sleep deprivation there is a marked decline in the responsiveness of lymphocytes and an even bigger fall in the activity of natural killer cells.
Sleep loss might play a role in the well-established connection between severe depression and impaired immune function. Depressed people generally sleep badly and have poorer immune responses. The more disrupted their sleep, the bigger the decline in their immune function. One study, for example, found that people who were suffering from depression following bereavement had fewer natural killer cells. The bereaved subjects were troubled by intrusive thoughts that often woke them or kept them awake during the night. The extent of the reduction in their natural killer-cell numbers was correlated with the amount of time they spent awake during the night: the more troubled someone was by their loss, the more disrupted their sleep and the fewer natural killer cells circulating in their blood. Sleep deprivation could be one of the mechanisms by which depression makes people more vulnerable to illness.
The relationship between sleep and immunity works in both directions. Not only does sleep affect the immune system, but the immune system also affects sleep. The immune reactions triggered by infection and illness can elicit alterations in sleep patterns. That is why infections are often accompanied by lethargy, loss of appetite, depressed mood and general malaise. Animals infected with influenza virus display a large increase in sleep about 24 hours after exposure to the virus. These changes in wakefulness are part of the body’s defence mechanisms and assist the recovery process. Human experiments, in which noble volunteers were injected with bacterial toxins, found that sleep is highly sensitive to the activation of the immune defences. Low-level infection tends to promote deep sleep. However, a full-blown infection accompanied by fever induces lethargy but typically disrupts sleep. You might have noticed that you sleep more deeply for a night or two when your body is fending off a potential infection, whereas when you are in the throes of a galloping illness you feel exhausted but lie for hours without sleeping.
The immune response to infection stimulates the release of chemical messenger substances that act on the brain to induce malaise, drowsiness, loss of appetite and sleep. During infection, a substance known as interleukin-1 stimulates the brain to induce deep sleep, while other interleukins trigger the fever that often accompanies infections. They do this by adjusting the brain’s temperature control centres – in effect, putting the body’s thermostat on a higher setting. That is why we feel hot and sleepy when we have a bad infection. The fever response is a defence mechanism found in all animals: the rise in body temperature makes life harder for the offending bacteria or viruses, and the lethargy forces the infected organism to curl up in a dark corner and sleep until it has recovered. It all makes good biological sense.
The brain and the immune system are interconnected through an elaborate network of chemical and neural communication channels. One important link between sleep, immune function and psychological stress is the steroid hormone cortisol. Sleep deprivation and prolonged stress both provoke an increase in the level of cortisol. After one night of sleep loss, your cortisol levels would typically be raised by about 45 per cent the next evening. It is not good to have elevated cortisol levels for too long, since cortisol has a powerful suppressive effect on the immune system. The functioning of the immune system is also intimately bound up with the 24-hour sleep – wake cycle and the circadian rhythms in hormone levels. Various aspects of immune function fluctuate in tune with the circadian cycle. Anything that disrupts the normal cycle of sleep and wakefulness therefore tends to disturb the immune system, with potential consequences for the body’s ability to defend itself against infection and disease.
The intimate relationship between sleep and immune function takes on a potentially huge practical significance when you consider how widespread sleep deprivation has become in society. Tired people are more likely to become sick people.
The Battle of Stalingrad (#ulink_9b00653d-4c92-584b-bd9a-f2e3f6199cb4)
O, I have passed a miserable night,
So full of fearful dreams, of ugly sights
William Shakespeare, Richard III (1591)
Prolonged sleep deprivation, uncontrollable stress and starvation make a lethal cocktail, as Hitler’s troops found to their cost during the Battle of Stalingrad in World War Two. In June 1941 German forces invaded the Soviet Union and were soon threatening Moscow. The capture of Stalingrad on the River Volga became a key strategic objective. Stalin decreed that the city must be defended to the bitter end. The titanic struggle that ensued cost the lives of at least 800,000 Axis soldiers and 1.1 million Soviet soldiers.
The fight for Stalingrad (now renamed Volgograd) began in earnest in the summer of 1942, as the Germans advanced rapidly towards its suburbs. There was fierce Soviet resistance and the fighting dragged on into the harsh Russian winter. By September 1942 the battle was being waged at close quarters among the buildings, cellars, sewers and bunkers of ‘the Stalingrad Academy of street-fighting’.
To increase the pressure on their opponents, the Soviet commanders ordered continual raids to be carried out by night. They did this partly because the Germans lacked protection from their air force at night, but mainly to induce exhaustion among the enemy. To augment the night raids, the Soviets fired flares indicating that an attack was imminent even when it was not. Their air force also attacked German positions every night. The Soviets kept up the psychological pressure throughout the night, with loudspeakers blaring out propaganda broadcasts, surreal tango music, or the sound of a ticking clock. The strategy was highly effective. ‘We lie exhausted in our holes waiting for them,’ wrote one German soldier. The German commanders begged for air support, citing their men’s exhaustion.
The German troops’ health started to deteriorate badly even before the dreadful Russian winter had begun to bite. There was a sharp rise in deaths from infectious diseases including dysentery, typhus and paratyphus. The actual prevalence of these diseases was not much worse than it had been a year earlier, but the numbers of infected men who were dying from them increased fivefold. It was as though the German soldiers had lost their capacity to resist infection. The Russians noticed this phenomenon, which they referred to as ‘the German sickness’.
In November 1942 the Russians launched a huge and ultimately successful counteroffensive that soon had the Germans encircled within the ruined city. But the Germans were under orders from Hitler not to surrender, and so they fought on through December while the Russians gradually tightened the noose. Conditions for the German troops became appalling as their supply lines were cut off and the Russian winter froze them. There was hardly any food and little or no medical care.
In mid-December 1942 the German military doctors in Stalingrad noticed a new phenomenon: more and more apparently healthy troops were suddenly dying for no obvious reason. The Germans were unsure whether the deaths were the result of starvation, exposure, exhaustion or an unidentified disease. A German army pathologist named Girgensohn, who was sent to Stalingrad to investigate the problem, became convinced that a combination of exhaustion, stress, cold and lack of food was responsible for the much higher death rate. The Russian night attacks and round-the-clock activity had caused severe sleep deprivation, and Girgensohn concluded that this had amplified the effects of the food shortage by ‘upsetting the metabolism’ of the exhausted Germans. We know now that one symptom of prolonged sleep deprivation is a marked increase in metabolic rate and hence the requirement for food. Whatever the precise explanation, the pressure was too much for the Germans. In February 1943 the Battle of Stalingrad finally ground to a halt, as the crushed and starving remnants of the German army surrendered.
Sleepless in hospital (#ulink_970a2ca6-868e-5135-aa5d-1fce1f4248e3)
I have the feeling that once I am at home again I shall need to sleep three weeks on end to get rested from the rest I have had.
Thomas Mann, The Magic Mountain (1924)
Sleep is good for you and lack of sleep is bad. It therefore seems odd that hospitals, which are supposed to promote recovery, are usually dreadful environments for sleeping. ‘The hospital bed,’ wrote one historian, ‘is one in which normal sleep is forbidden.’ A Punch cartoon of 1906 shows a patient being told to ‘wake up and take your sleeping-draught’. Things have improved since 1906, but not much.
Sick people really do benefit from sleep. We saw earlier how the brain and the immune system respond naturally to infection by inducing sleep. This helps the body cope with disease in several ways. The production of growth hormone occurs mainly during sleep, and growth hormone aids physical recovery by promoting the healing of mucous membranes and in other ways. The hormone melatonin, which is also produced at night, boosts immune responses, inhibits the growth of tumours and enhances resistance to viral infections. Conversely, sleep deprivation impairs immunity and slows the healing process. Given the importance of sleep for recovery, it is ironic that hospital patients are routinely subjected to conditions that make normal sleep almost impossible.
Sick people start with big disadvantages, of course. Pain is a powerful disrupter of sleep. Patients suffering from chronic, severe pain often become exhausted. Disrupted sleep is a common complication of burn injuries, for example. Studies have found that between half and three quarters of burns patients experience significant sleep disturbances. Sleep problems are common among cancer patients too. Fatigue can become one of the most distressing aspects of having cancer, severely reducing the quality of life. While medical treatments for cancer have advanced apace, efforts to improve patients’ quality of life by alleviating their fatigue have lagged behind.
To make matters worse, tired people are more sensitive to pain. Sleep deprivation lowers pain thresholds, generating a vicious cycle in which pain disrupts sleep, the resulting sleep loss makes the pain feel even worse, and so on. An investigation of patients with burns injuries uncovered a systematic link between the quality of their sleep and subsequent pain. Patients who slept poorly during the night experienced more intense pain the following day, because the fatigue intensified their perception of pain.
One of the worst places imaginable if you need a good night’s sleep is an intensive care unit (ICU). The combination of serious illness, serious drugs, constant monitoring, bright lighting and the aftereffects of surgery ensures that ICU patients are often subjected to severe sleep deprivation. And yet the ICU houses the sickest people in the hospital, with the greatest need for sleep. American researchers conducted an experiment to see if implementing regular ‘quiet times’ during the day would help ICU patients to get more sleep. Each day for two two-hour periods, lighting levels in the unit were reduced and the staff made a concerted effort to minimise noise. The ‘quiet-time’ regime worked: the patients were 60 per cent more likely to sleep during these quiet periods than at other times of the day. More flexibility over when patients are given their medication can also help them to get more sleep.
Sadly, the apparent neglect of sleep in hospitals is another reflection of the general disregard for sleep in medicine and society as a whole. Lack of sleep really does have very little to recommend it.
PART III Mechanisms (#ulink_be9ab661-a886-5eee-a451-329f6d4fd927)
5 The Shapes of Sleep (#ulink_70b8113c-3786-5379-a11c-7351d23b0377)
Sleep rock thy brain.
William Shakespeare, Hamlet (1601)
Now it is time to peer beneath the surface at the strange state of existence known as sleep – or, to be more precise, the two strange states of existence known as sleep.
All of human life is spent in one of three states. You are very familiar with one of them: it is called the waking state, or consciousness, and it forms the subject matter for almost everything that has ever been said, written, acted, painted or composed about humanity. When scientists analyse the mind, when novelists dissect the human condition and when biographers portray the lives of eminent individuals, it is the waking state they almost invariably describe. However, there are two other distinct states of existence that together account for at least a third of each life. They labour under the workaday names of Rapid Eye Movement (REM) sleep and Non-Rapid Eye Movement (NREM) sleep, and we are about to take a closer look at them.
A night’s sleep is a complex and cyclic process, comprising several distinct patterns of brain activity and behaviour, with alternating episodes of NREM sleep and REM sleep. We will follow the sleep cycle from the beginning, starting with the transition from the waking state. But before we do that, a quick word about how scientists know what is going on when we are asleep.
Measuring sleep (#ulink_1726e0c8-aadf-5969-b848-c38cd4d3615b)
Brains wave.
Owen Flanagan, Dreaming Souls (2000)
The sleeping brain reveals what is going on inside itself in various ways, both electrically and chemically. Since the middle of the twentieth century, the main tool for monitoring sleep has been the electroencephalograph. This machine exploits the fortunate fact that varying patterns of electrical activity within the brain manifest themselves as varying patterns of voltage changes on the surface of the scalp.
The brain comprises billions of nerve cells, or neurons, and although the electrical activity of an individual neuron is too faint to be detected outside the skull, it is possible to monitor the gross patterns generated collectively by large numbers of neurons. These show up as minute voltage changes, which can be detected by electrodes stuck onto the scalp. (The very first electrodes were small pins that were stuck into the scalps of stoical volunteers.) Thus, the brain emits electrical signals revealing information about its inner state. These tiny voltage patterns are amplified and displayed as the familiar ‘brain waves’ of the electroencephalogram, or EEG. (Confusingly, the machine is called an electroencephalograph, while the graph it produces is called an electroencephalogram, or EEG. To avoid nausea, I will use EEG to denote both the machine and its output.)
The EEG was invented in the 1920s by a psychiatrist named Hans Berger. It really came into its own in the 1950s when, as we shall see, it enabled the discovery of REM sleep. Before the invention of the EEG, scientists could only assess sleep by observing overt body movements, or the lack of them. Scientists still find it useful to record sleepers’ body movements, especially in studies of sleep patterns under natural conditions where the use of EEG would be too intrusive or too expensive. Nowadays, body movements are usually logged automatically, using a miniature recorder worn on the wrist.
Sleep laboratories use an extension of the EEG called the polysomnograph – a sort of somnolent variation on the polygraph. A polysomnograph records the EEG brain waves, together with other informative measures of the sleeper’s physiological state and behaviour. Electrodes placed near the corners of the eyes detect movements of the eyeballs, producing a trace known as the electro-oculogram, or EOG. Other electrodes placed on the chin and neck monitor the muscle tone (producing an electromyogram, or EMG) while electrodes on the chest record the heart rhythms (electrocardiogram, or ECG). Additional devices may record whole body movements, breathing, the flow of air through the nose and mouth, and the concentration of oxygen in the blood. In the early days of sleep science, these measurements were recorded as continuous pen traces on miles of rapidly unfurling paper, but nowadays the outputs are usually stored digitally.
In recent decades, brain scanning has become an increasingly important tool in sleep research. One of the main brain-scanning techniques is called positron emission tomography (PET). PET scans reveal the local patterns of blood flow and oxygen uptake within small areas of the brain by measuring how rapidly the tissue is using energy. Unlike some brain-scanning techniques, PET does not require the subject to sleep inside a large, claustrophobia-inducing scanning device. It therefore allows scientists to monitor sleep under conditions that are slightly closer to normality. Even so, the sleeping subject’s head needs to be kept absolutely still, which is usually achieved by pinning the head down with a special mask (the stuff of some people’s nightmares).
Most measurements of sleep are made in specialised sleep laboratories rather than people’s own homes. The underlying assumption is that the sleep patterns observed in the laboratory closely resemble the real thing. Fortunately, this turns out to be a broadly valid assumption. Comparisons have confirmed that for most people there is a reasonably good concordance between their sleep patterns at home and in the sleep laboratory. But there are some systematic differences. In particular, people tend to sleep for a slightly shorter period under laboratory conditions and to wake up slightly earlier than they would normally. They also have less bizarre dreams and fewer wet dreams. (Wouldn’t you?)
Falling asleep again, what am I to do? (#ulink_b330ab61-a9f6-5a33-a7d6-2ff7e618681b)
Warm beds: warm full blooded life.
James Joyce, Ulysses (1922)
Falling asleep is not an abrupt process, like turning off a light, although it can seem like that because you usually forget about it. Recordings of brain-wave activity and other physiological variables show that falling asleep is in fact a continuous process, which starts from a state of relaxed drowsiness and ends in the first or second stages of unequivocal sleep.
During that process of falling asleep you may find yourself temporarily suspended for several minutes between the worlds of waking consciousness and sleep. This transition phase is often accompanied by strange thoughts, dreamlike images and occasional hallucinations. In one of his short stories, Washington Irving described how the mind can roam far and wide while it is in this pre-sleep state:
My uncle lay with his eyes half closed, and his nightcap drawn almost down to his nose. His fancy was already wandering, and began to mingle up the present scene with the crater of Vesuvius, the French Opera, the Coliseum at Rome, Dolly’s Chop house in London, and all the farrago of noted places with which the brain of a traveller is crammed – in a word, he was just falling asleep.
These dreamlike experiences occur when we are in what is known as the hypnagogic state – a twilight zone partway between wakefulness and sleep. They are referred to as hypnagogic (or sleep-onset) dreams and they are distinct from ordinary dreams, which do not occur until much later in the sleep cycle. Hypnagogic dreams can contain all the basic elements of ordinary dreams, including bizarre plots, visual images and sounds, but there are fewer of these features in any one dream, suggesting that hypnagogic dreaming is a reduced version of normal dreaming. Similar dreamlike experiences can also occur at the other end of a night’s sleep, during the transition from sleep to wakefulness, when they are known as hypnopompic dreams.
The hypnagogic and hypnopompic states are strange and fascinating. In comparison with true sleep and ordinary dreams, they are also poorly researched and poorly understood. Indeed, the English language does not even have a decent name for them – unlike Italian, which has a single word for both (dormiveglia, or ‘sleep-waking’). In English, hypnagogic dreams are colloquially referred to by a variety of vague terms such as ‘faces in the dark’ or ‘visions of half-asleep’. As we shall see in a later chapter, many famous creative flashes and inspired thoughts have come to people while in the hypnagogic state.
During hypnagogic dreams we may see strange sights, hear strange sounds and think strange thoughts. As our wakefulness fluctuates, we may wake up again and consciously remember the strange things we have briefly been dreaming. This hypnagogic nonsense sometimes includes bizarre, invented words. The sleep researcher Ian Oswald recalled waking from one hypnagogic dream with the phrase ‘or squawns of medication allow me to ungather’ running through his mind. On another occasion he found himself musing on the hypnagogic thought that ‘it’s rather indoctrinecal’. A British magazine once printed a collection of hypnagogic ramblings sent in by readers. These included the immortal verse ‘Only God and Henry Ford have no umbilical cord.’
Hypnagogic thoughts and images can be more coherent, however. Charles Dickens often fell into a half-sleeping state while on one of his long nocturnal walks, and he could compose poetry while in this reverie. Dickens wrote of how, one night, he got out of bed at two in the morning and walked thirty miles into the countryside:
I fell asleep to the monotonous sound of my own feet, doing their regular four miles an hour. Mile after mile I walked, without the slightest sense of exertion, dozing heavily and dreaming constantly … It is a curiosity of broken sleep that I made immense quantities of verses on that pedestrian occasion (of course I never make any when I am in my right senses), and that I spoke a certain language once pretty familiar to me, but which I have nearly forgotten from disuse, with fluency. Of both these phenomena I have such frequent experience in the state between sleeping and waking, that I sometimes argue with myself that I know I cannot be awake, for, if I were, I should not be half so ready.
People who play lots of computer games sometimes experience ‘screen dreams’ as they fall asleep, in which they see vivid images of the game they have been playing. These screen dreams are also products of the hypnagogic state. The computer game Tetris, which requires the player to fit together coloured shapes as they cascade down the screen, is well known for provoking hypnagogic dreams. Scientists at Harvard Medical School investigated screen dreams by getting volunteers to play Tetris for several hours. Many of them experienced vivid dreams about Tetris as they fell asleep. Among the subjects in this experiment were five amnesiac patients who had extensive brain damage in their temporal medial lobes – brain regions crucial for conscious memory. Three of the five amnesiacs experienced hypnagogic dreams of Tetris even though they had no conscious memory of playing the game. This implies that the brain can generate hypnagogic dreams without input from conscious memory.
The length of time it takes you to fall asleep, once you have lain down and shut your eyes, is known as your sleep latency. It varies according to lots of factors. As we saw earlier, very short sleep latencies usually indicate sleep deprivation, whereas very long sleep latencies may signify other problems. A study of people living in rural Oxfordshire found that those with the longest sleep latencies typically described themselves as bored or mildly ill. You can make yourself fall asleep faster if you are minded to do so. Researchers proved this by giving volunteers a financial incentive to fall asleep quickly at various times during the day. The paid volunteers fell asleep faster than subjects who had no financial incentive.
Your body temperature has a big influence on how fast you fall asleep. A night’s sleep is normally preceded by a drop in core body temperature, and scientists have established that this drop in temperature actively facilitates the onset of sleep. Under normal conditions, the maximum rate of decrease in body temperature occurs about one hour before the onset of sleep. If the onset of sleep is artificially delayed, the drop in body temperature is attenuated – further evidence that the two are closely linked. The polymath Benjamin Franklin realised the importance of a falling body temperature in triggering sleep. He set out this practical advice in a 1786 essay called ‘The Art of Procuring Pleasant Dreams’:
Get out of bed, beat up and turn your pillow, shake the bedclothes well with at least twenty shakes, then throw the bed open and leave it to cool; in the meanwhile, continuing undressed, walk about your chamber. When you begin to feel the cold air unpleasant, then return to your bed, and you will soon fall asleep, and your sleep will be sweet and pleasant.
Benjamin Disraeli found that he was more comfortable when sleeping in hot weather if he used two beds, moving periodically from the hot, sweaty bed into the cooler one. Benjamin Franklin lit upon the same trick years earlier, but Franklin reckoned he needed four beds to be really cool. William Harvey, the seventeenth-century English physician who discovered the circulation of blood, similarly appreciated that cooling the body helps to induce sleep. According to his contemporary, the biographer John Aubrey, Harvey would tackle his insomnia by cooling himself down until he began to shiver:
He was hot-headed, and his thoughts working would many times keep him from sleeping. He told me that then his way was to rise out of his Bed, and walk about his Chamber in his Shirt, till he was pretty cool, i.e. till he began to have a horror [began to shiver], and then return to bed, and sleep very comfortably.
Another scholar who stumbled across the sleep-inducing properties of cool air was Lord Monboddo, an eccentric eighteenth-century Scottish nobleman and pioneering anthropologist. When Samuel Johnson and James Boswell visited Monboddo, the great sage and his biographer were surprised by their host’s behaviour. As Boswell recorded:
Lord Monboddo told me he awaked every morning at four, and then for his health got up and walked in his room naked, with the window open, which he called taking an air bath; after which he went to bed again, and slept two hours more. Johnson, who was always ready to beat down any thing that seemed to be exhibited with disproportionate importance, thus observed: ‘I suppose, Sir, there is no more in it than this, he awakes at four, and cannot sleep till he chills himself, and makes the warmth of the bed a grateful sensation.’
A less irksome way of achieving a similar effect is to take a hot bath an hour or two before bedtime. The bath will temporarily raise your body temperature. Over the following hours, your temperature will drop again and, all being well, this will help to trigger sleep. Experiments have confirmed that people do feel sleepier at bedtime after taking a hot bath. But the bath must not be too hot, too long or too close to bedtime, or it may have the reverse effect.
The fall in core body temperature that precedes sleep is accompanied by a small rise in the temperature of the hands, feet and other appendages. Blood vessels in your appendages dilate when you lie down to sleep at night, causing them to warm up. As they warm up so your body cools down, helping to send you off to sleep. Experiments have shown that warm feet assist the onset of sleep, bearing out another piece of folk wisdom. One of the best ways of predicting how quickly someone will fall asleep is to measure the temperature gradient across their body. The hands and feet are normally a degree or two cooler than core body temperature, but the temperature difference dwindles to nothing as sleep approaches.
A further demonstration of the linkage between warm appendages and the onset of sleep came from a study of people suffering from a disorder known as vasospastic syndrome. This condition is caused by faults in the physiological mechanisms controlling the peripheral blood vessels, which become less able to dilate. One of the main symptoms is cold hands and feet. As predicted, the cold-toed victims of vasospastic syndrome took longer than normal to fall asleep at night.
The importance of a declining body temperature means that artificial heat sources like electric blankets can disturb sleep. An electric blanket operating between the early hours of the morning and waking will typically increase your core body temperature by about 0.2 degrees Celsius. Even this small increase in body temperature is enough to disrupt sleep.
The sleep-inducing effect of a falling body temperature helps to explain why vigorous physical exercise, which raises body temperature, is not a good idea just before going to bed. It also reminds us why it is inadvisable to eat a large meal shortly before bedtime. The digestive processes that follow a large meal evoke a rise in metabolic rate, which in turn raises body temperature. In an ideal world, a large evening meal would be eaten at least three hours before bedtime. However, this helpful advice is of little use to the many people who work long hours and face long journeys to get home afterwards. They may have barely enough time to prepare and eat an evening meal before going to bed – another example of how lifestyles can conflict with good sleep.
One popular notion that reportedly fails to stand up to scientific scrutiny is that we fall asleep faster after orgasm. A group of enterprising researchers conducted an experiment in which they monitored the sleep of men and women under three different conditions: after the subjects had masturbated to orgasm, after they had masturbated without orgasm, and after they had simply read some nonsexual material. Recordings of their subsequent sleep yielded no evidence that masturbation, with or without orgasm, affected any aspects of sleep, implying that post-coital sleepiness has nothing to do with the attainment of orgasm. (You may find this hard to believe.) This is clearly an area crying out for more research.
The sleep cycle (#ulink_8aefcd07-4655-52e8-bff0-4d696acbd200)
Sleep flooded over him like a dark water.
Jorge Luis Borges, Labyrinths (1964)
Two broadly different states are conventionally bracketed together under the general heading of sleep: rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep. NREM sleep is further subdivided into four different stages, based on their characteristic EEG patterns. Each sleep stage has its own distinctive pattern of brain activity. The various stages and types of sleep alternate cyclically throughout a night’s sleep.
As you become sleepier, your EEG pattern changes. If you are tired enough, this can happen even when you are walking around and supposedly wide awake. The pre-sleep state of quiet restfulness is heralded by the appearance of brain waves of lower frequency and higher voltage, called alpha waves. If you are very sleepy, but still awake, your alpha waves will be accompanied by slow, rolling movements of your eyes. Nearly there. Then you are asleep.
The initial phase of sleep, which has the prosaic name of stage 1, typically lasts only a few minutes. Your muscles start to relax. If you are trying to sleep in a sitting position, the relaxation of your neck muscles will allow your head to slump forward, briefly waking you; your head straightens, you nod off again, and so on. hat is why you ‘nod off’. You can easily be roused into wakefulness from stage 1 sleep. If someone does wake you during stage 1 sleep you may be aware that you have been asleep, or you may be equally convinced that you have been awake the whole time. Stage 1 sleep is accompanied by a further slowing of the brain-wave patterns.
The next phase is known, predictably, as stage 2 sleep. This is signalled by the appearance on the EEG of two specific brain-wave patterns called K complexes and sleep spindles. The K complex is a single, strong wave that lasts less than a second. The sleep spindle is a brief burst of waves lasting less than a second. A sleep spindle on an EEG trace looks like a spindle moving along a loom, hence its name. During stage 2 sleep your eyes are still and your muscles are relaxed. You are less easily awoken by stimuli and you appear to an observer to be sound asleep. Altogether, stage 2 occupies about 45–50 per cent of a night’s sleep.
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Paul Martin
Тип: электронная книга
Жанр: Биографии и мемуары
Язык: на английском языке
Издательство: HarperCollins
Дата публикации: 16.04.2024
Отзывы: Пока нет Добавить отзыв
О книге: A brilliant overview of that most vital, most underrated and most elusive of human activities, sleep.Using the approach and skills he deployed to such successful effect on the relationship between mind and body in the prize-winning ‘The Sickening Mind’, likeable British popular science author Paul Martin here tackles the science of that most mysterious, elusive and alluring of human activities, sleeping, and draws on both cutting-edge neuroscience and classic literature to do so.We spend one third of our lives asleep, but know hardly anything about it, and can remember so little of it as we come out of it. Why?Are dreams the place we go to resolve our problems, emasculate our fears and rehearse our hopes? Why are we paralysed when we dream? Why did sleep evolve?And is anybody getting enough sleep?