The Vertebrate Clock: Localisation, Connection and Entrainment

Abstract

Our lives are based around a series of recurrent cycles. Some of these cycles reflect changes in our physical environment, such as the solar day or the passage of the seasons, whilst others are social, for example the alternation between the working week and the weekend/Sabbath, or the imposed schedules of shift work. We are adapted to these cycles and function effectively because our metabolism, physiology and behaviour undergo regular rhythmic changes which are generated by an internal “body clock” synchronised to our environment (Aschoff 1981; Aschoff et al. 1971; Wever 1979; Moore-Ede et al. 1983; Folkard et al. 1985). Should this synchrony break down, our mental and physical performance is impaired and we experience a generalised disaffect (Moore-Ede et al. 1983; van Cauter and Turek 1986; Ehlers et al. 1988; Moore 1991; van den Hoofdakker 1994). Such desynchronisation may occur for two basic reasons. First, the internal processes of the clock which generates and controls bodily rhythms may be disrupted, for example due to disease or as a consequence of old age. Second, when our habits and routines are forcibly altered, for example during jet lag or irregular working schedules, the environment provides conflicting information and the regular progression of internal rhythms may be suspended (Chap. 14, this volume). If we are to understand how we are synchronised to the environment and so identify novel therapies to overcome the problems associated with desynchrony, it is necessary to examine the internal processes which generate biological rhythms and to describe how they are influenced by external cues. The aim of this chapter is to review what is known of the neural basis of the vertebrate clock, how it controls daily rhythms and how it responds to physical and social cues.