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What Is Normal? Whatever the problems, sleep and slumber, dreams and dreaming have fascinated man ever since he evolved the wits to think about them. But not until the 20th century did truly scientific medical research get rolling. The results are summarized in a scholarly monograph, Sleep and Wakefulness, by Dr. Nathaniel Kleitman (University of Chicago Press; $12.50). Dr. Kleitman lists no fewer than 4,337 learned publications on sleep, but he winds up with the sobering conclusion that, even today, nobody can define the condition. The basic question remains unanswered: Is wakefulness the more natural and fundamental state, in which sleep is only a restorative interlude, or is sleep the truly normal condition?
From his eminence as the grand old sandman of science, Dr. Kleitman dismisses the popular theory that man has a "sleep center" in his brain that must be activated to lull him out of his nor mal wakefulness and into sleep. "The principal, if not the only mechanism involved," he says, "is a center or system whose activity induces and maintains wakefulness and whose inactivity leads to sleep."
Muscle Fatigue. What does it take to make the wakefulness center fall asleep? Aristotle noted that a heavy meal leads to somnolence, went on to speculate that sleep is caused by vapors rising from the stomach. Physicians have attributed falling asleep to temperature changes in different parts of the body. Neurologists have found complex explanations in various nerve bundles. Pavlov, who became famous by getting a dog to drool at the sound of a dinner bell, invented a theory of cortical inhibition.
Nonsense, says Dr. Kleitman: man goes to sleep when his muscles are so tired that they have to relax, though this is complicated by the tensing effects of emotions on muscles. The mere act of lying down leads to eventual relaxation of all but two muscle groups—the sphincters that remain contracted to keep the sleeper from soiling his bed. Muscular relaxation leads, by some mechanism that no one yet understands, to relaxation of the wakefulness center.
In the process, the temperature of the body drops about one degree. No man can lull himself to sleep, however, simply by cooling down his bedroom. His own internal thermostat will fight back. Not only will the discomfort of being chilled tend to keep him awake; it will make him shiver, and shivering speeds up the body's metabolism, which also heightens wakefulness.
Stored Energy. During sleep, the heart slows down from an average of 75 to 60 beats a minute. Breathing slows down, from an average 16 to 12 respirations a minute. Blood pressure falls. Sweating increases. The liver stores up glycogen ("animal starch") that will be needed during the day for conversion into blood sugar that is in turn converted into energy. The kidneys go on working, endlessly filtering metabolic poisons out of the blood, but because the sleeper has no water intake, his first morning urine is more concentrated and darker than during the day.