Neuroanatomical and neurophysiological aspects of sleep: basic science and clinical relevance

This is an exciting period for basic sleep research, because we are now beginning to understand some of the mechanisms controlling the changes in consciousness associated with sleep and wakefulness. Witness the recent discoveries of a probable genetic involvement in narcolepsy, the identification of hypothalamic structures promoting sleep, and the mounting evidence that adenosine is an endogenous sleep factor. We review these and other recent developments that help us understand the neuroanatomical and neurophysiological basis of some sleep disorders. For a detailed discussion of specific sleep disorders and clinical issues, the reader is referred to other sources. Overviews are also available covering rapid eye movement (REM) and non-REM sleep physiology, the role of humoral factors in sleep, and the relationship between the immune system and sleep. In fact, where appropriate, here we draw directly on material from our earlier summaries of work in the field. We begin with a brief review of the organization of sleep and wakefulness to provide the background for the subsequent discussions of the anatomy and neurophysiology of the neural control of different vigilance states and associated sleep disorders. For example, a brief description of the neural mechanisms of REM sleep will be followed by an outline of selected sleep disorders related to REM sleep. In summary, we make no attempt here to include all sleep disorders and only review a few selected examples, those in which there is an understanding based on knowledge of central nervous system physiology. Unfortunately we are not now able to include sleep apnea, because the discovery of sleep apnea not only was a defining moment for clinical sleep research, but to this day remains the principal presenting complaint at some sleep disorder clinics.