[00:00.49]It is fairly clear that sleeping period must have some function,
[00:05.82]and because there is so much of it the function would seem to be important.
[00:10.62]Speculations about is nature have been going on for literally thousands of years,
[00:16.43]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.
[00:25.82]'Rest', in terms of muscle relaxation and so on,
[00:30.33]can be achieved by a brief period lying, or even sitting down.
[00:35.68]The body's tissues are self-repairing and self-restoring to a degree,
[00:41.39]and function best when more or less continuously active.
[00:45.55]In fact a basic amount of movement occurs during sleep
[00:50.06]which is specifically concerned with preventing muscle inactivity.
[00:54.74]If it is not a question of resting the body,
[00:58.16]then perhaps it is the brain that needs resting?
[01:01.57]This might be a plausible hypothesis were it not for two factors.
[01:06.37]First the electroencephalograph
[01:09.81]shows that while there is a change in the pattern of activity during sleep,
[01:14.56]there is no evidence that the total amount of activity is any less.
[01:19.56]The second factor is more interesting and more fundamental.
[01:23.57]Some years ago an American psychiatrist named William Dement published experiments dealing with the recording of eye-movements during sleep.
[01:33.92]He showed that the average individual's sleep cycle is punctuated with peculiar bursts of eye-movements,
[01:41.23]some drifting and slow, others jerky and rapid.
[01:45.43]People woken during these periods of eye-movements generally reported that they had been dreaming.
[01:52.10]When woken at other times they reported no dreams.
[01:56.11]If one group of people were disturbed from their eye-movement sleep for several nights on end,
[02:01.70]and another group were disturbed for an equal period of time but when they were no exhibiting eye-movements,
[02:08.24]the first group began to show some personality disorders
[02:12.26]while the others seemed more or less unaffected.
[02:15.46]The implications of all this were that it was not the disturbance of sleep that mattered,but the disturbance of dreaming.
