Sleep and research- EEG effects and benefits of sleep

Based upon distinct changes in the EEG and upon another phenomenon-the appearance of rapid eye movements (REM) at some points -sleep investigators divide sleep into a series of stages: In stage 1, light sleep begins. There are slow EEG waves, 4 to 6 cycles a second. In stage 2, medium deep sleep, slower waves appear and voltage increases. In stage 3, deeper sleep, voltage increases still more. And in stage 4, deepest sleep, very large slow waves of high voltage appear on the EEG. But when deepest sleep is reached, it is not maintained long.

Instead, there is a return to stage 1 sleep. And with the return to stage 1, REM or rapid eye movements appear. And the progression through the various stages occurs about every 90 minutes. Thus, however much you may think so upon full awakening in the morning, you never sleep through a night "like a log." In fact, many changes take place. There are muscle movements at various stages of sleep, less often during stage 1, quite often during moving from one stage to another. Actually, in stage 1, the heart beats faster, breathing quickens, muscles tend to relax, as if, some investigators suggest, you were settling down to dream much as you would settle down in your seat before the curtain goes up in the theater. It is in stage 1, with the appearance of REM that you dream. And you dream whether you remember the dreaming or not.

Investigators, after many thousands of studies, know enough to realize that, for whatever reason dreams are needed, all people dream just as all people sleep, and the dreams are not haphazard but appear at regular times in the sleeping cycle. The need for dreaming has been demonstrated by investigators who have awakened subjects from sleep every time REM began, depriving them of their dreaming periods, allowing them to sleep at other times. The result: impaired functioning, physical and psycho- logical.

The EEG has established that some of the older ideas of sleep, such as the popular notion that sleep is always deepest and soundest at the beginning of the night and lightest in the morning near awakening time, are false.  Work in the sleep laboratory, you can reconstruct what happens a night's sleep in this fashion: As you relax and close your eyes, pulse is steady and even, your body temperature gradually to [all, and your brain waves show an even frequency of about  second, called alpha rhythm. You are awake but relaxed, to move into sleep.