Development of the Concept of Sleep-Wake-Promoting Systems in the Brainstem and Hypothalamus

Abstract

A main part of fundamental knowledge about sleep regulation roots in the recognition of reciprocally antagonistic sleep-wake-promoting influences originating in brainstem/hypothalamic neuronal networks and in their dynamic interplay. All the presently known concepts and models of sleep regulation are essentially based on the anatomy and function of these subcortical networks. From the beginning of this century, the Harvard School of sleep research and the Lyon sleep research group have introduced important concepts about the working of the flip-flop model of “sleep switch” governing sleep/wake alternations and tried to connect these views with the earlier ideas explaining sleep cyclicity. These results have suggested that the subcortical neuronal assemblies have indeed a governing role in the EEG and behavioral changes during the sleep/wake cycle. However, within the NREM sleep period, robust dynamical changes take place, about which the flip-flop model has nothing to say about. NREM sleep cannot be taken as a “stable” state. Growing evidences about the “microstructure” of NREM sleep present sleep as an ever-changing fluctuating state intermingled with microarousals, strongly ­contradicting to this simple model.