The Physiology Of Sleep

It was four o'clock in the morning. Private David S. bent over a wash basin to clean up, glanced casually into the mirror above the basin – and received the shock of his life. He saw cobwebs on his face, a mass of clotted dirty material clinging to his cheeks, nose, chin. He tried to brush the stuff off, but it stuck fast. Then he looked down at his hands, and noticed with horror that they were covered with cobwebs too. "I called for help," he later said, "and the corpsman came in and said there was nothing there, and I was just having trouble with my eyes!"

Private S. was neither a mental patient nor a chronic alcoholic. He was suffering from lack of sleep. In fact, at the time of his terrifying hallucination he had remained awake for a total of 65 hours. He is one of more than 70 enlisted men who have volunteered to serve as experimental guinea pigs in a study still under way at the Walter Reed Army Institute of Research in Washington, a study of the basic biological nature of sleep. His case illustrates an important finding in all such investigations.

Contrary to popular belief, you do not sleep to rest tired muscles or to rebuild tissues after a day's work. Even if you went three to four days without sleep, it's a very good bet that a routine examination would not reveal anything out of the ordinary. Your heart would beat at about its usual rate. Your blood pressure would be normal and so would blood-sugar levels, indicating that you had plenty of chemical fuel to burn. You might pass these and other physical tests with flying colors. But you'd be in real trouble mentally.

Sleeplessness strikes hardest at centers of the nervous system, and the case of Private S. is typical. One of his fellow volunteers saw snow falling around a light bulb in the ceiling. Another was found wiping "grease" off a perfectly clean wall, and a third tried to stamp on imaginary bugs crawling along the floor. As you might expect, symptoms tend to become worse the longer the ordeal lasts. To date the record at Walter Reed is about a hundred sleepless hours, but there are far more grueling sessions on record.

Peter Tripp, a New York disc jockey, participated in the most recent no-sleep marathon some nine months ago. He stayed awake nearly eight and a half days (201 hours and 13 minutes, to be precise), experiencing a wide variety of hallucinations. Floors tilted and began rolling and waving like sheets of rubber; lights had halos around them; the suit of one visitor seemed to be made up of thousands of twisting worms. Incidentally, Tripp does not hold the world's record. During World War II a Canadian scientist managed to hold out for 10 consecutive days and nights. By the end of that session he had an insane gleam in his eyes, thought people were plotting against him, and showed other signs of major mental illness.

All the evidence points to the same conclusion. We sleep chiefly for the benefit of our brain. This is the organ which carries the main burden of prolonged insomnia and cracks first under strain. It is the busiest and most complex part of the entire body, a communications center seething and buzzing with activity every moment of the day. The eyes register a thousand and one details – images which are converted into electrical signals flashed along nerve fibers. At the same time signals come from many other sense organs, from your ears and nose and from millions of heat, cold, pain and touch detectors imbedded in the skin. Whatever you do, wherever you go, you are continually prodded and goaded. You are bombarded with signals, an estimated hundred million electrical pulses every second, which represent the state of affairs in the environment around you.

So we know why sleep is important. It is something like turning down the volume control of a howling radio. It shuts out for a while the hubbub of life which would drive us mad if there were no relief. It brings us a temporary measure of peace. But we have much to learn about the actual mechanism of sleep, the details of what happens when we begin dozing off. One of the world's leading investigators of this problem is Dr. Nathaniel Kleitman of the University of Chicago, who has been studying sleep for more than 35 years. A plausible theory is emerging from his work and from the work of others at many research centers.

Sleep, it has been learned, cannot be considered as an isolated phenomenon. It represents an idling state of the brain, which can exist in a whole spectrum of different states. Think of a scale of mental alertness with deep sleep toward the low end of the scale and 100-percent attention at the high end. We spend most of our time living somewhere between these two extremes. Life-or-death (continued on page 76) Physiology Of Sleep (continued from page 65) emergencies – for example, avoiding a smashup on the highway – draw on our fullest powers of concentration. The danger may be over in a few seconds, but during that period the brain and nervous system attain a state of alertness so intense and so vivid that the experience may leave us exhausted.

All irrelevent detail is ignored and every important detail comes into sharp focus when survival is endangered. At other times, the brain tends to take it easy. One psychologist has estimated that on the average we are fully alert for no more than a minute or two out of every hour. The rest of the time we go about in almost a trance, functioning as high-grade robots or semi-robots. The brain does as much as possible automatically and our awareness level is fairly low during routine everyday activities. This is the state generally referred to as "being awake."

The general level of activity starts falling toward the end of the day. The brain has been so busy receiving, analyzing and transmitting signals that it usually starts to falter. It behaves something like an overworked motor which sputters and misfires in protest. During the evening you may have episodes of microsleep, brief lapses or blackouts of consciousness which you do not notice. They last for only a second or so and come at a rate of perhaps one every 10 or 15 minutes. Also, the lapses become longer and more frequent the longer you stay awake.

Microsleep is a telltale sign of changes among certain cells in an important region of the brain, the brainstem or bulging extension of the spinal cord into the skull. This white cable, which is about four to five inches long and as thick as your thumb, includes a diffuse network of inter-tangled nerve fibers which may function as a wakefulness or alerting center. It is a Grand Central Station of the nervous system, a meeting place for signals representing sensations from all parts of the body. Many of the signals normally continue to travel upward along ascending nerve pathways to the brain's highest center, the cortex – and as long as they keep coming in full force we are awake.

But here's what happens when you begin dozing off. Things quiet down in the wakefulness center. The number of nerve impulses from brainstem to cortex becomes smaller and smaller. Research using brain-wave machines, which provide charts of the activity of groups of nerve cells, indicates that there are various stages in falling asleep. The first stage occurs as soon as you turn in for the night, close your eyes, and relax without thinking about anything in particular. At this point the automatic pen of the machine writes a rippling "signature" on moving'chart paper, brain waves produced at a rate of about 10 a second.

The pattern soon changes from smooth continuous ripples to brain waves which come in bursts. Now your mind is wandering; you are beginning to drift off and dream. Later there is another characteristic change in the record. As the bursts become fewer and farther between, they are replaced by large waves which rise and fall like ocean swells and appear at a rate of two or three a second. These "slow rollers" mark the arrival of deep dreamless sleep which, short of serve coma or death itself, represents the closest we can come to escaping from the pressures of the outside world.

Of course, the escape is not complete. Even in deepest sleep we cannot shut ourselves off entirely. Discomfort is always with us, and the body protests after staying too long in one position. Stiff muscles send nagging signals to the brain until we assume new horizontal postures. There is no such thing as sleeping like a log. Even relatively inactive sleepers shift an average of about three times an hour; restless sleepers shift seven to eight times an hour. For reasons as yet undetermined we change positions more frequently during the second half of the night, and more frequently in the fall than in the spring.

Incidentally, the brain knows exactly where we are at all times – and confines our unconscious movements in bed accordingly. A person who is accustomed to an oversized bed may switch to a narrow Army cot, but the odds are that he won't fall off. A traditional way of sleeping in Japan involves the use of a tiny wooden pillow, a kind of raised platform originally designed to prevent elaborate hairdos from becoming messed. But sleepers manage to go through night after night of tossing and turning, and still keep their heads on the pillow.

The sleeping brain also maintains communications with the outside world. Some nerve channels always remain clear for messages of special significance. Some gates always remain open. For example, you may be able to sleep soundly through thunderstorms, the neighbours' late parties, or the clanking of trolley cars. But the sound of your name whispered softly will be enough to rouse you. Similarly, a mother will waken promptly when her baby cries from the next room, although she ignores louder noises closer to her ears.

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Among current problems concerning sleep, or lack of it, the most widely discussed is insomnia which has been called a typically American ailment, and with good reason. Insomnia may be a symptom of a wide variety of physical disorders ranging from indigestion and bad tonsils to diabetes and heart trouble. But in more than 90 percent of all cases the cause is mental. Emotional tension is a notorious enemy of sleep – and the job of keeping up with, or getting ahead of, the Joneses is calculated to keep tensions at a high pitch.

Excitement, persistent worry and mulling over problems keeps the cortex buzzing with nerve signals. Controlling this hubbub is largely a matter of psychology and individual taste rather than set rules based on medical fact. For example, considerable nonsense has been written about the benefits of "scientifically" designed mattresses and innersprings, and Dr. Kleitman reminds us that "a large portion of mankind sleep . . . on the ground, sometimes on mats, sometimes on the bare floor or soil." But logic has little to do with the case. If a particular mattress suits you best, use it and it will help put your cortex at rest. Some people find that a nightcap helps them doze off. Others swear by a glass of milk (hot or cold – there are two schools of thought on this procedure), an hour of relaxed reading, a light snack, a large meal, or no food at all. The routine that seems suited to you is the routine to follow.

As far as barbiturates and other sleep-including drugs are concerned, it is generally agreed that small doses can be taken safely – assuming that your doctor knows about it, and approves. All so-called hypnotic drugs act on the nerve cells of centers involved in sleep. A normal cell "fires," or transmits signals, only if it is affected by a stimulus of a certain strength. A barbiturate makes cells more resistant to such firing. It raises their threshold so that they will respond only to stimuli of greater-than-average strength. Thus, the cells of a drugged cortex react sluggishly and nervous activity slows down sufficiently to bring on sleep.

But immoderate use can cause dangerous upsets in the workings of nerve cells. They begin to tolerate drugs so that doses have reduced effects. The result is a vicious process of larger and larger doses which may lead to aggravated insomnia, nervous breakdown, and even addiction. Extreme overdoses, a common method of committing suicide, cause death by knocking out centers which regulate breathing and blood circulation. Alcohol, by the way, resembles hypnotic drugs in that it also raises the threshold of nerve cells in the cortex. At first we may feel stimulated because lower centers are released from cortical control. Later alcohol may produce a soporific effect, however, which is one reason why doctors advise their patients not to take sleeping pills after an evening of (continued on page 108)Physiology(continued from page 76) steady drinking. It is wise to take only one nerve-affecting drug at a time.

Moderation is also the rule for energizers, substances which may keep you awake. The list includes caffeine in tea and coffee – as well as many varieties of "pep pills" generally containing Benzedrine, Dexedrine or related compounds. These drugs lower instead of raise nerve-cell thresholds. The cells work on a hair-trigger principle, becoming more sensitive and firing under weaker-than-average stimuli. Energizers tend to keep nerve centers on the go.

The danger, of course, is that a person may remain active too long. Energizers may keep you awake, but they make the brain work at an abnormal pace and they can never postpone indefinitely the effects of prolonged insomnia. Although Peter Tripp took pep pills during his 201 sleepless hours, they did not prevent the onset of severe mental symptoms, temporary though they were.

Normal sleep, too, poses some interesting questions. For one thing, doctors would like to know why sleep requirements vary so widely from one individual to another. Most of us sleep about eight hours a night, although studies indicate that seven hours are probably ample for the average person. Still, some people need as little as four or five hours, while others must have 10 hours or more. According to some authorities, the difference seems to be largely a matter of heredity. In other words, an individual who can get along on relatively little sleep has probably inherited an extra-tough nervous system, just as people inherit a large body build, blue eyes or curly hair. But we do not know what makes a nervous system tough or weak.

Somnambulism or sleep-walking is also a mystery. We have already mentioned that the brain may function automatically, and there are special nerve centers which play a major role in automatic actions. Sleep-walking occurs most often among growing children, perhaps because these centers have not yet developed to the point where they work smoothly under the control of higher centers. When the condition lasts, psychiatrists suspect either faulty brain development or a neurotic illness.

Another sign of cerebral activity during slumber is the fact that some people seem to have timing devices built into their brains. They can wake up at 6:15 or 9:15 on the dot, simply by deciding on the time before they turn in. This ability may be related to a recent discovery of fundamental biological significance.Investigations at Princeton University hint that every cell of the brain contains a biological clock, some kindof innate rhythm which marks time. But no scientist can explain how certain people are able to "set" these invisible timekeepers at will.

One of the most important of all findings about sleeping and waking concerns another persistent body rhythm known as the diurnal cycle. No one is fully awake when he gets out of bed in the morning. Your brain takes time to warm up, and you operate at subpar levels until it does. Tests show that your reflexes are slower than normal, your mind tends to wander and you make more errors in daily tasks before you hit peak efficiency, which may not happen for four to eight hours. Then your efficiency starts dropping off again, reaching its low point around bedtime.

Body temperature provides a sensitive index of the diurnal cycle. At bedtime your temperature had dropped a few tenths of a degree below the normal level of 98.6 degrees Fahrenheit. Moreover, it is likely to drop further during the night, perhaps as much as a degree or two. It begins climbing after you get up, and its peak coincides with your working-efficiency peak. Such measurements show that most of us fit into one of two broad categories, "day" people and "night" people.

Day people tend to be quick wakers. Their temperature climbs at a relatively fast rate when they wake up. If you belong to this category, you probably jump out of bed as soon as the alarm clock rings feeling alert and in good spirits. In short, you probably make a good breakfast companion. But, if possible, it's generally a smart thing to avoid a night person early in the day. His body temperature rises slowly; he feels drowsy and irritable. He'd like to spend the morning in bed, and resents the whole business of getting up.

The diurnal cycle represents a regular pattern which is established when we are about two years old. Why we should be day or night types at such an early age is a question that hasn't yet been answered. But the cycle persists year after year.

More than 20 years ago Dr. Kleitman and one of his students, Bruce Richardson, spent a month living in a large chamber in Mammoth Cave, Kentucky. The idea was to find out whether people could become conditioned to changes in the traditional 24-hour pattern of sleeping and waking. The investigators lived on a 28-hour schedule – nine hours of sleep and a 19-hour working day – with breakfast shortly after waking, and two larger meals seven and 13 hours later.

The experiment proved one thing: you can definitely do something about your diurnal cycle, providing you are young enough. Richardson had no trouble fitting into the new pattern. Within a week his body temperature had shifted from a 24-hour to a 28-hour rhythm. But he was in his twenties. Dr. Kleitman, who was 43 at the time, found the going rough: "I had difficulty in falling asleep, or woke up too early, or both. I offered the greater resistance to change, and I also happened to be the older."

These and other pioneer experiments hint at what may lie ahead. We still have an enormous amount to learn' about the physiology of sleep, because it involves the workings of the human brain – the most complex and mysterious structure we know of in the physical universe. But the next step, the big challenge of the future, is an active and organized program to modify our sleeping habits. That means a deliberate effort to alter old habits, and alter them radically. Think how much we've changed since caveman days. During the long and accelerating march of human evolution we have developed new kinds of homes, new diets, new tools and weapons and means of transportation, new customs and ethical standards.

But our basic sleeping habits do not differ appreciably from the habits of our ancestors who lived thousands of centuries ago. We still devote a large proportion of our lives to sleep, far too large a proportion in the opinion of some investigators.

In other words, the problem is to increase our waking time. Dr. Kleitman notes that our present cycle is eight hours of sleep and 16 hours of wakefulness. He believes that by careful conditioning and training it will be possible to take slightly more sleep, say up to 10 hours, and "stretch" it further so that we can stay awake longer before turning in again. How long could we stay awake under such conditions? "My own guess," reports Dr. Kleitman, "is that 40 or 50 hours is the limit."

Another interesting approach is based on the fact that we spend a total of only about one or two hours a night in deep sleep. Now suppose that researchers discover a drug that acts directly on centers in the brainstem, puts us into deep sleep right away – and keeps us there for a controlled period. Two hours of such sleep might be all we'd need. Apparently the idea has occurred to Soviet scientists too, because a recent report from Moscow predicts that within a century "no one will sleep more than one or two hours a night."

One thing is certain. Sooner or later man will take things in his own hands as he has always done in the past, and he will reduce his sleeping requirements. The stakes are high. After all, if we could do with two instead of eight hours' sleep a night, we'd add the equivalent of more than 5000 waking days or nearly 14 years to the average lifetime. We study sleep not only for knowledge of the brain, but also as a promising way to prolonging a full and fascinating life.