The role of chronobiology in sleep disorders medicine.

This review is concerned with circadian (approximately 24 h) aspects of chronobiology, and how they relate to sleep disorders medicine. We begin with an introduction to the key concepts and paradigms of circadian rhythms research in general, including a description of homeostatic and circadian determinants of sleep timing. This is followed by a brief history of chronobiology in relation to sleep disorders medicine. Both animal and human circadian rhythm studies are considered. We trace historical changes in the relative emphasis placed on social contacts, light, and melatonin in human circadian rhythms research. Special attention is given to free-running, forced desynchrony, and ultra-short sleep/wake cycle findings of particular relevance to sleep disorders medicine. The latter part of the review comprises a description of the circadian rhythm sleep disorders, highlighting insights derived from basic circadian rhythms research, including recent advances in molecular genetics. We conclude that the role of chronobiology in sleep disorders medicine is profound and pervasive, and that the two disciplines will move ever closer as a natural function of important new insights into sleep and sleep disorders provided by basic circadian rhythms research.