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.
