Archived Columns
The True Nature of Sleep II
October 9, 2000
When I first got into the business of studying sleep, nearly half a century ago, the prevailing view was that sleep is simply the end of wakefulness; the brain turning off until the morning light turned it on again. There was a great deal of interest in the qualities of deep sleep and light sleep. The very words "deep sleep" connotated rest, restoration, the likelihood of awakening energized. "Light sleep" meant sleep was easily disturbed, less restorative, the brain "less" turned off. As I have and will point out repeatedly, we have not accomplished much in terms of weaning humanity from this point of view. Not only is maintaining these archaic views totally wrong, but it delays and obstructs the need to know, in as much detail and with as much understanding as possible, what sleep is.
Fact. Rest does not equal sleep. More than 70 years ago, Professor Nathaniel Kleitman at the University of Chicago asked volunteers to go to bed at home as they did every night, turn out the light, but not to sleep. All the volunteers reported that they had fallen asleep without intending. Kleitman transferred the study to his laboratory where the volunteers could be watched. It was clear almost immediately that if individuals succeeded in avoiding sleep while resting in bed all night, they felt sleepy the next day. In other words, they were anything but rested. Resting in bed but not sleeping for two consecutive nights was totally impossible. Unless the volunteers were made to get out of bed and walk around, they could not be kept awake.
More recently there has been a great deal of research on the relationship of vigorous exercise during the day and sleep at night. It is a proven fact that resting during the day does not decrease the amount of sleep at night, nor does vigorous exercise during the day increase the amount of sleep at night.
While being horizontal in bed is preferred by almost everyone, it is obvious that sleep can occur in a wide variety of positions and postures. If a chair is sufficiently comfortable, it is possible to sleep an entire night in a sitting position. In unusual circumstances, an individual can experience short bouts of sleep while standing, and even walking or running. We can only say that the horizontal posture, a comfortable bed and bed clothes, darkness, quietness, relaxation all favor the occurrence and continuity of sleep. Because of the great decrease in muscular activity, we use fewer calories during sleep. This slowing of metabolism could be a major advantage to sleeping every night, if food were scarce.
Of course, there is much more to say about sleep. In the first place, research over the past couple of decades has decisively established that the sleeping brain is an active brain. Because so many people believe that sleep occurs when the brain is "turned off," I like to say, "If that is your image of sleep, then hear this, 'the brain never sleeps!'" Thus, while the body may rest during sleep, the brain does not.
The next fundamental fact is that there are two entirely different kinds of sleep. One kind of sleep is called REM, and the other is called non-REM. Both kinds of sleep occur every night, and they alternate with one another every 90 minutes on the average. They are very different from one another, although both fulfill the fundamental property of sleep discussed in my 8/28/2000 commentary, The True Nature of Sleep I. We are not conscious of the world around us, we are perceptually disengaged during both REM sleep and non-REM sleep. The two chief characteristics of REM sleep, in addition to the occurrence of rapid eye movements, are (1) its association with vivid dreaming and (2) its association with a flaccid paralysis of all the voluntary muscles except the diaphragm. When an entire night of sleep is considered, we typically see an orderly sequence of sleep stages defined by brain wave patterns. Deep sleep occurs early in the night and gives way to lighter sleep and longer REM periods later in the night.
Although we are making major strides in sleep research and education, the importance of sleep is still a long way from having the recognition it deserves, but there is light at the end of the tunnel. we must remain hopeful.
Stay tuned.
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