[00:01.49]Lesson 19
[00:03.88]The stuff of dreams
[00:12.89]What is going on when a person experiences rapid eye-movements during sleep?
[00:21.48]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.
[00:32.48]Speculations about its nature have been going on for literally thousands of years,
[00:38.80]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.
[00:48.75]'Rest', in terms of muscle relaxation and so on, can be achieved by a brief period lying, or even sitting down.
[00:58.93]The body's tissues are self-repairing and self-restoring to a degree, and function best when more or less continuously active.
[01:09.16]In fact a basic amount of movement occurs during sleep which is specifically concerned with preventing muscle inactivity.
[01:19.58]If it is not a question of resting the body, then perhaps it is the brain that needs resting?
[01:26.60]This might be a plausible hypothesis were it not for two factors.
[01:31.71]First the electroencephalograph (which is simply a device for recording the electrical activity of the brain by attaching electrodes to the scalp)
[01:42.12]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.
[01:52.77]The second factor is more interesting and more fundamental.
[01:57.24]Some years ago an American psychiatrist named William Dement published experiments dealing with the recording of eye-movements during sleep.
[02:08.31]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.
[02:20.49]People woken during these periods of eye-movements generally reported that they had been dreaming.
[02:27.40]When woken at other times they reported no dreams.
[02:31.86]If one group of people were disturbed from their eye-movement sleep for several nights on end,
[02:37.64]and another group were disturbed for an equal period of time but when they were not exhibiting eye-movements,
[02:44.19]the first group began to show some personality disorders while the others seemed more or less unaffected.
[02:51.60]The implications of all this were that it was not the disturbance of sleep that mattered, but the disturbance of dreaming.