Acute Reversal of the Sleep-Waking Cycle in Man

Abstract

PAST studies of the sleep-waking circadian cycle in man emphasized the temporal relationship to other rhythmic physiological and chemical functions.¹It was implicitly assumed in these studies that sleep is a unitary process. Recent evidence, however, clearly indicates that sleep is composed of recurring short-term physiologic events.^2,3In man, during each daily sleep period, a consistent sequence of sleep patterns occurs, characterized by four or five recurrent 90-minute cycles. Future studies of circadian phase relationships between sleep and physiologic variables should take into account the qualitative and quantitative differences between sleep stage patterns. We have begun to study the time relation of sleep stages and neuroendocrine processes.⁴The method of cycle phase shift of 180° (sleep-waking cycle inversion) has been used in man.^5-8This report describes the changes in sleep pattern when normal young adults were subjected to an acute inversion of sleep-waking cycles in