We spend approximately one third of our lives asleep. This is more time than we spend looking after our children; socializing with our friends; and working. Think how much effort we put into childcare, friendships and our jobs, and how little time we spend thinking about improving our sleep. We tend to take sleep for granted – we think of it as a revitalizing process that somehow should just “happen”.
We are born with the gift of effortless sleep: when babies need to sleep they merely close their eyes and drift off. But by the time we reach adulthood, we have been taught to regulate our sleep habits according to the customs of our society. This learned behaviour supplants our ability to sleep naturally.
However, before we can take steps to improve our sleep, we need to understand it. In this chapter we explore what sleep is, and why and how we do it. We look at all the many ways in which sleep manifests itself – from the sleep–wake cycles of animals (and even plants) to the sleeping patterns of people from different cultures throughout the world.
All living things sleep. Some of them, such as humans, insects, plants, bacteria and many animals, switch in short-term cycles between rest and activity, while others undertake one prolonged stretch of inactivity – such as hibernating animals. However, despite the universality of sleep, and even despite the fact that sleep has been a source of fascination since ancient times, sleep research is still in its relative infancy.
When the ancient Greeks talked of Hypnos, they were referring to a mysterious god of sleep, who was said to live in a dark cave, and was the brother of Death and the son of Night. These dark associations suggest that the ancient Greeks were mistrustful of sleep – a state that they believed overpowered the brain against its will. Over time, medical men and philosophers tried to explain that state more scientifically. One enduring suggestion was presented by Aristotle (384–322 BCE) who believed that sleep was caused by the brain being “gassed” by the vapours of our food as the food decomposed in our stomach.
Notions of the brain being fumigated in the way that Aristotle had suggested or, alternatively, flooded with blood, abounded until the fifteenth and sixteenth centuries, when scientists discovered that such occurrences were physiologically impossible. The field of sleep research seemed at a loss – and by the eighteenth century the idea re-emerged that blood rising to the head put pressure on the brain, causing it to shut down temporarily.
After several other unsubstantiated theories, the breakthrough came in 1929 when German psychiatrist Hans Berger invented the EEG machine – the electroencephalogram. Berger claimed that this marvellous machine could measure different states of alertness by placing electrodes on a subject’s scalp and recording the electrical activity of their brain (see pp.34–5).
Equipped with an EEG machine, in the 1950s the American psychologist Nathaniel Kleitman and his student Eugene Aserinsky made great leaps in the field of sleep research. Watching the sleep of infants, they noticed that for short periods the babies’ eyes moved about rapidly behind the closed lids – and that each short period of eye movement corresponded with certain brain rhythms, read from the EEG. Thus REM (rapid eye movement) sleep was unveiled, shortly followed by further experiments and readings from the EEG showing that there were four other distinct stages of sleep (see pp.36–7). Most importantly, scientists came to realize that the brain is not passive or inactive during sleep as had been thought for hundreds of years – it chooses to sleep as a necessary part of our wellbeing. The first positive steps in sleep science had been taken – only sixty years ago.
Sleep is far more than simple rest. We all do it and we all know from personal experience that its composition, depth and intensity, and its ability to refresh us, vary considerably. But how can we begin to define such a complex state?
We can start to characterize sleep by using our own powers of observation. Try watching someone as they sleep. They are probably lying inert in a peaceful, comfortable environment. They should be breathing steadily and quietly, and they may jerk and turn over from time to time. We may see their eyes moving beneath their eyelids, indicating that they are dreaming. The person is likely to be unresponsive to anything going on around them – although if we talk to them, they may give an incoherent reply. If we expose them to a strong enough stimulus, such as the sound of their baby crying or the ringing of an alarm clock, they will immediately awaken, although it might take a moment or two for them to become fully alert.
With these characteristics in mind, we might then look at how scientists have attempted to define sleep, drawing parallels with our observations where we can. For example, some researchers contrast sleep with wakefulness, describing the two as obverse sides of the same coin. If wakefulness is a time when we have complete self-awareness – when we can voluntarily do certain things such as eat, drink, think and work – sleep is the opposite. Just as we observed, in the sleep state we are generally physically inactive, except for minor unconscious movements, such as scratching. Special brain mechanisms dampen the amount of information that flows in from the senses, while other brain signals relax or even paralyze many of the body’s main muscles. And although we are mentally active while we sleep – we have thoughts and see images in our dreams – our brain processes lack the structure and logic that they have when we are awake.
One final route to defining sleep is to break the state down into its physiological stages. On average, we clock up between six and nine hours of sleep at night, during which time we go through four or five separate cycles, each lasting roughly ninety minutes. These cycles are interspersed with brief periods of wakefulness, which we do not remember. To further complicate matters, each sleep cycle has five stages (as elaborated by Kleitman’s student Dement): drowsiness, light sleep, two stages of deep sleep, and REM sleep. A healthy adult’s sleep comprises around 25 per cent deep sleep, 50 per cent light sleep and 25 per cent REM.
Evolution, nature’s own judge of the effectiveness of living things, would not require us to spend approximately a third of our lives asleep unless sleep offered some distinct physical or mental advantage. Before we begin the path toward sleep improvement, it is instructive to consider why we sleep at all.
We know that most sensory stimulation is shut out during sleep and our muscles are fully relaxed – some of them even temporarily paralyzed. We might say, then, that we sleep in order to force ourselves to rest. However, we would be wrong to interpret sleep simply as a means of energy conservation. The amount of energy saved during sleep is unremarkable: a person weighing 200 pounds (approximately 91 kg) burns off calories during sleep at a rate of 80 calories per hour. The same person sitting quietly uses up calories at a rate of 95 calories per hour – so the energy saving during eight hours sleep (compared with eight hours waking rest) is roughly equivalent to the number of calories in a glass of low-fat milk!
In a similar vein, some scientists have claimed that deep sleep is fundamental to repairing the daily wear and tear on the body, and that dreaming sleep restores the efficiency of the brain. We can see how we might arrive at this conclusion – it is an extension of the knowledge that animals with fast metabolisms sleep longer than those with slow ones. In other words, we sleep so that the body and mind are forced to stop and undertake internal maintenance work – in this way we are prevented from burning ourselves out. However, mounting evidence suggests that the body does not repair itself during deep sleep any more than during light sleep or wakeful rest, and that most of the brain is as active while we are dreaming as it is when we are awake (in fact, many psychologists believe that the activity of our brains during sleep – when we are in a period of dreaming sleep – is essential for our emotional and mental wellbeing; see pp.122–5).
So where does this leave us? We do not know for sure when sleep evolved, how it evolved, nor whether it evolved to have one or more functions. But the one thing of which we can be sure is that sleep is essential to survival – bacteria, plants, animals and humans all undergo periods of sleeping and, if it were not essential, evolution would have cast it aside from one or all of these living organisms many thousands of years ago.
So far we have learned that sleep is difficult to define and that the reasons for sleeping are elusive – even to the experts. Perhaps, then, we should step back and see if we can identify any keys to sleep that might provide a basis for sleep improvement.
The most obvious first step is to examine what we see in the world around us – beginning with nature. Think of the daily cycle of a daisy, say. The flower opens its petals with the dawn and closes them as the sun sets. Its nourishment (occurring through a process called photosynthesis, which converts the sun’s rays into “food” – in the forms of oxygen and sugars – for the plant) is governed by the turn of each day from light to dark. We might therefore say that for the daisy (and thousands of other flowers and plants, of course) “work” (photosynthesis) occurs during the day, and “rest” occurs during the night – a pattern which seems very familiar to us. Making a direct comparison with human behaviour and the natural cycles of human life (see pp.28–9), we might conclude that taking note of the earthly cycle of light and dark is of fundamental importance to the quality of our sleep.
Apart from looking at plant life, scientists find it instructive to study the sleep behaviour of animals. Many experts believe that one of the keys to sleep lies embedded in the fact that different kinds of mammals have varying sleep times. For example, the brown bat is active for only four hours each day. Similarly, the North American opossum manages to clock up about eighteen hours of sleep each day. At the other end of the spectrum are the ruminating animals, such as cows and horses, which spend much of their wake time in a state of drowsiness, and may explain why they sleep as little as three or four hours in twenty-four hour period. The variations of sleep patterns between the species depends greatly on their diet and metabolism rate. Animals also teach us that sleep is posture-specific – even crustacea adopt specific body positions and show changes in muscle movement when they rest.
By looking at the natural world we learn of three key influences on human sleep: the natural cycles of light and dark; metabolism; and sleeping posture – which for humans means our environment as well as the position in which we sleep.
Swiss sleep researcher Irene Tobler has spent her entire career determining whether or not animals sleep and how their sleep is controlled. Among her more unusual discoveries is that cockroaches and goldfish sleep. But how can we tell? The way Tobler did it was to keep the goldfish and cockroaches moving about for long enough so that they had to have missed a period of sleep usual to their sleep cycle – and then (when she stopped pestering them!) she observed what happened. Having been deprived of sleep, the cockroaches and the goldfish became still for a protracted period of time – suggesting that the sleep deprivation had led to an increased need for them to rest. Tobler’s discoveries have played an important part in leading sleep researchers to the conclusion that all animals – not just mammals – sleep.
One of the most frequently asked questions about sleep is, What is a “normal” amount of sleep? If only it were that simple! Before we can begin to improve our sleep, we must understand one other fundamental principle about the way in which sleep works: namely that the amount we need varies from person to person. Sleep times depend partly on the way in which we are brought up and partly on our biological make-up. Furthermore, the unanswerable question ignores one important factor – we should not be asking simply, How much sleep do we need?, but also, When should we take it?
A siesta – an afternoon nap, usually taken during the hottest part of the day – is standard in many Mediterranean and tropical regions. Some might think that this is a luxury and that those who take a siesta benefit from “extra” sleep. In fact, things tend to balance out and, in cultures where the siesta is common, people usually stay up much later into the night than in non-siesta countries. Overall, siesta-takers may get around eight hours sleep (like most of the rest of us), broken into two unequal chunks (the first, a short burst of two or three hours; the second, a longer stretch of five or six).
Historically, the American Navajo people believed “A man lying down during daytime is a lazy man,” but before the working day became a nine-to-five entity, all Western sleep patterns may have been more broken up. Some research has shown that the sleep of medieval people quite often occurred in three distinct parts – a siesta in the afternoon, an early evening nap, and another, longer sleep until dawn.
But is this arrangement of short bursts of sleep any better for us than one long, rambling sleep period? Certainly, most research suggests that we are not physically designed to sleep in a single block of time and that a nap during the day and a longer period of sleep during the night is exactly the way in which nature intended we should sleep. Indeed, “polyphasic” sleep (sleeping more than once in a 24-hour period) is the most common pattern for sleep throughout the animal kingdom with “monophasic” sleep (a single sleep period) lagging far behind.
There are no rules about how much sleep we need – we must listen to our bodies. Our society tends to dictate that we sleep in a “monophasic” pattern – a single period of sleep every twenty-four hours, which usually occurs during the night. Do not worry if your sleep time seems short (say around four or five hours) – some of us are built simply to need only a few hours. Similarly, while sleeping more than nine hours a day is rare, it is not cause for undue concern unless social factors (such as a job, or school) are affected. If you can answer yes to the following questions, you are probably achieving the right amount of sleep.
• Do you fall asleep quickly (in under twenty minutes)?
• Do you sleep right through without waking in the night?
• Do you wake up in the morning bright and alert?
Our sleep patterns vary throughout our lives. In general, we tend to need less sleep as we get older. An awareness of how, when and why the changes occur in our sleep can help us to separate our natural decline in sleep duration from sleep problems.
After we are born we sleep for a total of up to eighteen hours a day, experienced as bursts of sleep which are interspersed with periods of wakefulness, usually to feed. At three to four years of age, we have a total of around twelve hours sleep. We grow rapidly at this age, so we need mostly “deep” sleep (this is actually a scientifically-accredited stage of sleep and not simply a colloquial term; see pp.40–41), which we experience mainly during the first half of the night.
During puberty we might assume that our sleeping patterns would be disrupted by the profound biological changes we experience. However, between twelve and eighteen, our sleep pattern (including the stages of sleep that we go through – from light, to deep, to dreaming and so on) changes very little. What does change is our awareness of our own social and sexual status. This increased awareness of self is thought to disrupt our sleep by intruding into our dreams, making them unpleasant, anxious, or erotic. Adolescent sleep is also influenced by peer and school pressures – especially during the week – resulting in sleep deprivation on school nights, and prodigious amounts of catching up at weekends!
During early adulthood, from the ages of eighteen to thirty, our sleep comes under new pressures as our lifestyle changes. While sleep patterns are generally established by now and we usually get the right amount of sleep, it is subject to the damaging influences of our changing circumstances – the pressures of a new regime of work and new financial responsibility, increased alcohol consumption, sharing a bed with someone else (perhaps someone who snores), newborn babies and so on. As we get older, sleep quality tends to worsen further – we tend to take less exercise and so gain weight, statistically we drink even more alcohol, and the years of anxiety that have built up in our minds and bodies release themselves in our dreams. Sleep during old age is mainly light and we suffer more frequent disruptions. Is it any wonder, then, that by the time we reach our 70s, we tend to compensate by napping during the day!
Taking an overview of a lifetime of sleep, what remains unclear is how many changes in sleep duration are irreversible. Having less deep sleep as we get older may be inevitable, but it does not necessarily mean that our sleep is less refreshing. Whatever age we are, we should always try to improve our sleep, so that we can enjoy each moment of wakefulness to the full.
The improvements we make to the quality of our sleep usually build up gradually, often so slowly that day-by-day changes are barely noticeable. Why not keep a sleep journal? This can be an invaluable tool for assessing what is going on in your sleep, before, during and after you start to tackle any sleep problems.
To help you get started, I have devised a “Sleeping Table”, charting the progress of one night’s sleep (a completed example is given below). It spans twelve hours from 9pm to 9am. In the evening note down anything you do, eat or drink between 9pm and the time when you try to go to sleep. Mark the moment you begin trying to sleep with a cross. Next morning, judge the point at which you actually fell asleep and mark it with a dot. If you got up in the night, draw an upward arrow and make a note of what you did (perhaps you had a glass of water or went to the bathroom). Draw a jagged line along the scale between the hours when you think you slept badly. For the period(s) when your sleep was peaceful, draw a solid line. Draw a dotted line for the period in the morning when you were semi-conscious, and an upward arrow to indicate when you got up. The exercise opposite tells you how to monitor your sleep over a 14-night period using this table as part of the process.
The Sleeping Table
EXERCISE ONE
Follow the steps in this exercise for 14 consecutive days, without trying to improve your sleep. Two weeks should be long enough to give you an overview of how your sleep changes in coordination with variations in your lifestyle – after a night out with friends, a stressful day at work, days off, a difficult incident with your partner, and so on. Once you have your overview, try some of the improvement techniques in this book for one month, then repeat the experiment.
1. Prepare your journal. On a single sheet of paper, make a template page. Write “Day” and leave several lines of space where you can make notes about the events of your day. Beneath this, draw a Sleeping Table (described opposite). Leave space for any annotation to the table, then write the numerals 1 to 10 across the page. Note down that 1 represents “very drowsy” and 10 represents “very alert”. Copy this template 14 times and write days and dates at the top of each page for the 14 days of your experiment.
2. Each evening complete the Day part of the journal and fill in the Sleeping Table. Next morning, as soon as you wake up, circle a number between 1 and 10 to indicate how drowsy/alert you felt on waking.
3. At the end of the two weeks, what can you learn about how occurrences in your daily life are reflected in the quality of your sleep? What steps can you take to neutralize the effects of the day on your nighttime rest?