Sleep - The Great Restorer
We spend a third of our lives asleep, and yet it is only within the last 20 years or so that scientists have started to make a really thorough study of what, exactly, sleep is and why we need it. The study is certainly long overdue, for sleep - if you stop to think about it - is a strange twilight state, in which the body is incapable of any purposeful thought or action and yet is still 'ticking over' and can respond to strong stimuli - such as the ring of an alarm clock.
It is not surprising that primitive Man had his own theories about sleep. One such belief was that during sleep a person's soul wandered off to commune with the spirit of the night. The orthodox Jews looked upon sleep as a kind of transient death, and gave thanks to God for the return of their souls in the morning. The Ancient Greeks were the first to attempt a scientific explanation for sleep. The philosopher Aristotle related sleep to the heart's activity and to the 'evaporation attendant upon the process of nutrition'.
Today, the layman thinks of a good sleep as an opportunity to 'recharge his batteries', and this is not far from the modern scientific explanation. Scientists believe, however, that sleep is rather more than just a good rest.
The first thorough scientific investigation of sleep was started in the early 1950s in the United States by a team led by Dr Nathaniel Kleitman. They intensively studied a number of volunteers through a complete night's sleep. They measured the electrical activity of the subjects' brains and hearts, their temperatures and blood pressures, and the oxygen they consumed.
The most interesting results came from the electroencephalograph, the machine that measured the subjects' electrical 'brain waves'. To measure the tiny electric currents in the brain, small metal electrodes are pasted on to certain regions of a person's scalp. These transmit the minute electrical signals to the machine, where they are amplified and made to operate a system of pens which trace out the patterns of voltages in the brain across a continuously unwinding sheet of graph paper. These patterns are known as the electroencephalogram, or EEG.
Dr Kleitman found that sleep is not simply a straightforward drift into an unconscious world. Rather, it is characterized by a progression of rhythmic cycles representing different phases of brain function.
Most important of all, sleep in which dreams take place seems to be quite different from dreamless sleep.
The sleeping person goes through four stages of non-dreaming, or- as it is termed by scientists - orthodox, sleep. While he is relaxed but still awake, his EEG shows a characteristic rhythm called the alpha rhythm. He then becomes drowsy and goes into what is called stage I sleep, from which he can be awakened quite easily.
Then he goes into stage II sleep, which is just slightly deeper, and through to stage III and stage IV sleep, which are the deepest kinds of sleep. The brain waves in stages III and IV are large and slow; they are known as delta rhythms. The person is
now much harder to awaken.
After about one hour of orthodox sleep, the person drifts back into the lighter stages of unconsciousness. A strange phenomenon now takes place. His eyes begin to dart about under his eyelids as though he were watching a film. His muscles become very relaxed, and reflex responses to certain stimuli no longer function.
The heart rate, blood pressure and breathing become irregular. If the subject is a man, his penis becomes erect.
The rapid eye movements (or REMs) correspond to definite changes in the EEG, and a person woken up during REM sleep almost always reports dreaming. So this kind of sleep is called dreaming sleep or - because of its resemblance to the waking state- paradoxical sleep.
During an average night, a person spends about 1 to 2 hours in dreaming sleep, divided into five or six periods. We all dream, even those who claim they never do. Doctors believe that these people simply do not remember their dreams. And it is not only human beings that dream; all seeing animals do. (Every dog-owner knows of the times when his sleeping pet seems to be chasing an imaginary cat.) Blind people dream just as much as those who can see, but their dreams may be different. People born blind have audiotactile ('hearing and feeling') dreams, but even these are accompanied by the characteristic rapid eye movements. If blinded later in life, people continue to have visual dreams even many years after losing their sight.
What function do the two types of sleep have? One modern theory, put forward by Dr Ian Oswald of the University of Edinburgh, Scotland, is a sophisticated version of the 'recharging the body's batteries' idea. It suggests that orthodox, non-dreaming sleep aids the growth and renewal of general body tissues, while paradoxical sleep serves the same purpose for the tissues of the brain.
On this view, babies probably sleep so much because they are rapidly building up both brain and body tissue. And the lesser amount of sleep taken by old people may be related to the fact that their bodies are renewing smaller amounts of tissue.
Several pieces of experimental evidence back up Dr Oswald's theory. During earlier experiments on addiction, Dr Oswald and his colleague, Dr Stuart Lewis, injected themselves for a week with small doses of heroin, which causes slight brain damage.
After stopping the drug, there was a sudden increase in the two researchers' paradoxical sleep - as the theory would predict, since the damaged brain tissue was then being replaced.
On the function of orthodox sleep, two American researchers have found that athletes who exercise during the day (and thus use up general body tissue) spend more time in orthodox sleep of stages ill and IV during the night. In Edinburgh, Dr Oswald and his team have performed an experiment on people with an excess of thyroid hormone. This hormone, like exercise, 'burns up' the body fast. The scientists discovered that subjects with thyroid excess tend to have a greater degree of stage ill and stage IV sleep.
The function of dreams themselves has been the subject of speculation for many years. Sigmund Freud and other psychoanalysts believed that dreaming provided a release for natural drives and conflicts mainly of a sexual nature - that were repressed by social pressures.
Quite another theory has been put forward by London psychologist Dr Christopher Evans. He draws an analogy between the brain and a computer. From time to time, a computer's programs- the sets of instructions that control its operation - need to be revised, updated and in some cases erased. This must be done when the computer is 'off-line' - that is, uncoupled from the system that it controls.
In the same way, Dr Evans suggests, the brain has to get rid of its old programs, and it does so when it, too, is 'off-line' asleep.
So, according to this theory, dreams are just fragmentary glimpses of the sorting, clearing and modifying processes whereby our personal computer programs are kept up to date.
Whatever their function, dreams are clearly essential, for certain sleeping drugs that reduce the amount of REM sleep may have distressing side-effects. In an experiment carried out in France, for instance, cats which were deprived of dreaming sleep by drugs died in three weeks. In Man, lack of dreaming sleep- whether natural or as a result of drugs - may be linked with certain mental disorders.
At the University of Chicago, an experiment was carried out on people who complained that they slept poorly. A group of 16 'good' sleepers were matched with 16 'bad' sleepers, and recordings were taken while both groups slept. Those who complained of sleeping poorly did actually sleep less than the good sleepers. They took longer to get to sleep, woke up almost twice as frequently as the good sleepers, and were more restless. They had higher heart rates, pulse volumes and body temperatures. They also spent less time in REM sleep. Perhaps most significantly, the researchers found that poor sleepers tended to be people who had neurotic and psychosomatic tendencies.
Acute episodes of the severe mental disease schizophrenia often seem to be preceded by difficulty in getting to sleep.
In one study, out of several hundred hospital patients admitted for psychiatric disturbances, 70 per cent suffered from sleep disorders before they were admitted for treatment. Many of them had been to their doctors and had been prescribed tranquillizing drugs, which had the effect of reducing their dreaming sleep. Among these patients there was a higher rate of suicide attempts than among those given a different sort of drug, an anti-depressant. Patients who complained that they had been dreaming less also showed a greater tendency to suicide.
Insomnia, the most common sleep disorder, can be of two kinds - the kind experienced by people who just cannot get to sleep, and that in which the person cannot remain asleep. It has been suggested that sedatives used for one kind may be inappropriate for the other.
Emotionally triggered insomnia may be due to excessive brain activity from a certain area stimulating the whole brain, while inability to remain asleep may be due to a lack of some chemical within a certain part of the brain making it difficult for the brain to remain unaroused. Many of those who imagine they have insomnia probably only suffer from light sleep.
But insomnia is not the only kind of sleep disorder. A patient may suffer exactly the opposite complaint - falling asleep when he does not want to. Narcolepsy, which is a tendency to black out at inopportune moments, is an 'attack' of REM sleep - an abrupt drop from waking into dreaming sleep. Violent anger or laughter may make narcoleptics so weak with emotion that they fall to the floor in a deep sleep resembling a black-out.
Sleep loss appears to encourage narcoleptic attacks. One of the common treatments for narcolepsy is to give the patient an amphetamine - a stimulant - to help him stay awake.
Unfortunately, amphetamines also reduce REM sleep. It is possible that as a result narcoleptics are depriving themselves of REM sleep during the night and compensating with REM sleep attacks during the day. A dream-enhancing drug taken during the night might counter this effect.
Since the brain's activity is clearly of vital importance to the quality of our sleep, what are the brain mechanisms involved in sleep? The overall control of sleep and wakefulness seems to be directed by a central part of the brain called the reticular formation. Experimental animals in which cuts are made in the connections between this part of the brain and the cerebral cortex (the 'seat of consciousness') fall into a deep coma and do not wake up.
Physiologists believe that a constant stream of nerve signals must reach the cortex from the reticular formation for the person to remain awake. During the day, a large number of signals flow out to the cortex, and the person is alert; at night the number of signals drops, and the person becomes drowsy and falls asleep. It could be that the reticular formation itself is stimulated by a chemical that is produced by the body in varying amounts over a 24 -hour cycle, for such a cycle seems to be built into the human metabolism.
A lot less is known about brain function in REM sleep, but a small part of the brain called the hippocampus seems to be involved in some way. Scientists have discovered that single electrical stimulations of the hippocampus will produce 'brain waves' resembling paradoxical sleep. The hippocampus is known to be associated with memory and emotional reactions.
In Japan and the United States, scientists have done a great deal of research in recent years into other states of consciousness, such as meditation. The EEGs of meditators show they never fall asleep.
Through practice they have acquired a technique which helps them to remain in a state of relaxed wakefulness. Their EEGs show large, slow alpha rhythms.
Can sleep be put to positive use? In the 1960s, the Russians - who have tended to regard time spent in sleeping as time wasted - spent great sums on research into sleep learning. The basis of the system is that a tape recorder plays a message which is supposedly learned by a person hearing it while he is asleep. Recently, a group of researchers at Cambridge University performed rigorous experiments to test the claims of the Russians that such a method of learning is successful. The Cambridge workers' conclusion was that learning during sleep is impossible.
Yet, in spite of the failure of such attempts, sleeping and dreaming are obviously of g1·eat benefit to Man. Any attempt to play around with the cycle of sleeping and waking incurs loud protests from the human metabolism.
In January 1959, a 32-year old American disc jockey called Peter Tripp undertook to stay awake for 200 hours - more than eight days. Glad of the opportunity to observe the effects of lack of sleep on the human constitution, specialists from all branches of medicine went to Times Square in New York to attend him.
During the 200 hours they gave him a multitude of medical examinations, psychological tests and tests of performance. For the first time the whole world saw the mental deterioration which takes place during sleep starvation.
Peter Tripp found it difficult to stay awake from the beginning. After two days he began to suffer from visual illusions; for example he began to complain of cobwebs in his shoes. By about 100 hours he was finding even simple mental tests a torture and was unable to concentrate. After 120 hours he came running out of his hotel room convinced that the drawer he had just opened was on fire. By 170 hours his condition was painful to observe; he became unsure of his own identity and went around asking people to tell him who he was. And finally, at the end of 200 hours, when a doctor in rather conservative clothes arrived to examine him, he ran from the examination room convinced that the doctor was an undertaker and was going to bury him alive.
When the ordeal was over and Peter Tripp had slept for 13 hours, all signs of mental deterioration and hallucinations vanished, though for three months afterwards he suffered from a mild depression. Subsequent experiments have shown that during sleep loss the heart rate goes up, and stress hormones in the blood increase.
Within 48 hours, signs of biochemical changes appear. The energy metabolism of the body is altered and shows a severe decline at 120 hours, coinciding with the onset of temporary mental illness. Experiments such as these are never really experiments in total sleep deprivation, however, because after 60 hours the volunteer tends to slip into so-called microsleeps, each lasting only a few seconds - proof positive, if any more were needed, of our bodies' need for sleep. Although he had no scientific data to go on, Shakespeare was obviously very close to the truth when his character Macbeth described sleep as 'chief nourisher in life's feast'.