Counting Sheep: The Science and Pleasures of Sleep and Dreams. Paul Martin

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

      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