Sleep Regulation: Circadian Rhythm and Homeostasis

Abstract

W. R. Hess characterized sleep as “.... the expression of a predominance of the trophotropic component of the autonomous nervous system and a preventive measure against exhaustion …” (Hess 1965). His concept of alternating trophotropic and ergotropic states resembles the present-day view of a circadian rest-activity rhythm. The trophotropic state and the circadian rest state have in common the predominance of physiological processes subserving energy conservation and restoration. They include, in addition to sleep, lipolytic processes of energy metabolism (Le Magnen et al. 1968; Danguir and Nicolaidis 1980) coupled to a low rate of feeding and drinking (e.g. Borbély 1977) and a low level of body temperature (Eastman 1980). The recognition of the integrative functions of the autonomic nervous system was at the root of the ergotropic-trophotropic state concept. The discovery of the existence of a central circadian oscillator was the major event in circadian rhythm research. Thus it became clear that the various physiological processes occurring typically during the circadian rest-phase are not merely a consequence of behavioural rest or sleep, but are under the direct control of a circadian pacemaker. The evidence was obtained from animals and people who lived under schedules without 24-h time-cues, and showed dissociations of their sleep-wake rhythm from the rhythms of body temperature or corticosteroid secretion, although sleep-related components were still evident (Weitzman et al. 1979; Eastman 1980). The results of rhythm research have therefore not only given a new significance to the concept of alternating ergotropic and trophotropic states, but have also shed light on the intrinsic control mechanisms of sleep and waking.