Timing of REM and stages 3 + 4 sleep during temporal isolation in man

During nonentrained sleep--wake conditions in man, healthy adult subjects spontaneously develop "long" biological days (greater than 35 hr) in addition to the normal, approximately 25 hr day. The ratio of sleep to total time remains constant (approximately 0.30), with long sleep episodes occurring approximately 180 degrees out of phase with the short sleep episodes. The timing and amount of REM sleep advance to an earlier time within the sleep episode during free-running, whereas stage 3 + 4 sleep is related to the initiation and course of the sleep process itself. The REM--NREM cycle length does not change, comparing entrained and nonentrained conditions. The study of the chronophysiology of humans under nonentrained conditions may serve as a model of the chronopathology of sleep--wake changes which occur in sleep disorders associated with depression, narcolepsy--cataplexy, sleep--wake dyssomnias, delayed sleep phase insomnia, and aging.