It is fairly clear that the sleeping period must have some function, and because
there is so much of it the function would seem to be important. Speculations
about its 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. In l960 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.