Biogenic amines and the states of sleep.

In the past 10 years the study of sleep mechanisms has developed very rapidly and has become one of the major fields of neurophysiological and psychological research. This rapid growth is in part due to some discoveries which have changed the classical neurophysiological picture of sleep from the concept of a passive resting state of the brain to that of a heterogeneous and complicated succession of active phenomena. Very seldom in the history of physiology has so much effort been devoted to the description, quantification, classification, and delimitation of such a complex phenomenon of almost totally unknown function. For this reason, I find it unnecessary to present a detailed review of the phenomenology of sleep and attempt instead to discuss the mechanisms involved in sleep. I first outline the four major concepts which have changed the classical theory of sleep. Second, I describe the neuropharmacological and histochemical data which have made possible the link between structural data and functional mechanisms. Finally, I present some recent findings which have led to the belief that a complex of monoamine-containing neurons are of paramount importance in the process underlying the succession of sleep states.