Counting Sheep: The Science and Pleasures of Sleep and Dreams

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?

‘… 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

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

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.