It is fairly clear that sleeping period must have some function, and because
there is so much of it the function would seem to be important. Speculations
about is nature have been going on for literally thousands of years, and one
odd finding that makes the problem puzzling is that it looks very much as if
sleeping is not simply a matter of giving the body a rest. 'Rest', in terms of
muscle relaxation and so on, can be achieved by a brief period lying, or even
sitting down. The body's tissues are self-repairing and self-restoring to a
degree, and function best when more or less continuously active. In fact a
basic amount of movement occurs during sleep which is specifically concerned
with preventing muscle inactivity.#
If it is not a question of resting the body, then perhaps it is the brain that
needs resting? This might be a plausible hypothesis were it not for two
factors. First the electroencephalograph (which is simply a device for
recording the electrical activity of the brain by attaching electrodes to the
scalp) shows that while there is a change in the pattern of activity during
sleep, there is no evidence that the total amount of activity is any less. The
second factor is more interesting and more fundamental. Some years ago an
American psychiatrist named William Dement published experiments dealing with
the recording of eye-movements during sleep. He showed that the average
individual's sleep cycle is punctuated with peculiar bursts of eye-movements,
some drifting and slow, others jerky and rapid. People woken during these
periods of eye-movements generally reported that they had been dreaming. When
woken at other times they reported no dreams. If one group of people were
disturbed from their eye-movement sleep for several nights on end, and another
group were disturbed for an equal period of time but when they were not
exhibiting eye-movements, the first group began to show some personality
disorders while the others seemed more or less unaffected. The implications of
all this were that it was not the disturbance of sleep that mattered, but the
disturbance of dreaming.&