ABSTRACT
The daily circadian rhythm is driven by an endogenous clock in the suprachiasmatic nucleus with period of about 25 h, entrained to 24 h by the day-night cycle. Sleep deprivation is accompanied by very little physiological change, and limited cognitive changes. At the end of periods of sleep deprivation, only about 20-25% is recovered on the following 2 or 3 nights. Extending sleep deprivation of rats beyond what has been possible voluntarily in humans causes death after about 4 weeks. There are no persistent psychological effects of rapid eye-movement (REM) sleep deprivation that are different from those of general loss of sleep. People who claim that they never dream have just as many REM sleep periods as others, and they are nearly as likely to report dreams when awoken during these periods. Long-term memory traces of the dreams are apparently not formed during sleep, so they are mostly not recalled on waking.
