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Sleeping
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feedback mechanisms to ensure that the aim is achieved ? Are there some minimum necessary amounts of sleep and of dreaming, and if these are not allowed, is there full compensation by more sleep and dreaming later on ? It seems at first obvious that sleep is for rest and recuperation - but why should the brain alone need to recuperate rather than other tissues ? The heart for instance never rests.
Perhaps it is a mistake to look at sleep only or mainly as a rest for the brain. It is reasonable to think that inany bodily activities require periodical recuperation and that providing for this is the reason for the physiological changes that accompany the various sorts of sleep. The best known are the changes in adreno-corticotropic hormone (ACTH), which controls the secretion of cortisol by the adrenals, so that it is three times higher on waking in the morning than at midday. Since the adrenal cortex is responsible for promoting many activities that are responses to 'stress', we have here real evidence of the filling of a sort of 'reservoir during sleep.
Similarly, production of growth hormone (somatotropin) is at a maximum during the first hours of sleep, that is during a period mainly of quiet sleep. After a day of heavy bodily exercise, there is increased quiet sleep. 6. Sleep Requirement
Infants sleep nearly sixteen hours throughout day; children need ten or eleven hours. Most adults average seven or eight hours each night. Middle-aged people require slightly less sleep. In old age, naps become frequent.
The need for sleep increases during pregnancy and illness. Anxiety, depression and physical or mental exertion also lengthen sleep. Researchers theorize that additional REM time --- the result of longer sleep -- restores the brain and helps it to integrate new experiences. In less stressful periods, demands on the brain are reduced, decreasing REM time. REM deprivation actually benefits some people. In a 1975 experiment at the Georgia Mental Health Institute, patients bospitalized for depression improved wiren they were deprived of REM sleep.
