Contribution of sleep physiology to depressive pathophysiology.

Among the best characterized neurobiological changes in mood disorders are specific alterations in electroencephalographic (EEG) sleep, including disinhibited rapid eye movement (REM) sleep and suppressed slow wave sleep. A strong link between mood disorders and sleep is that depressive symptoms are alleviated by one night of sleep deprivation and reoccur after sleeping. Sleep underlies homeostatic and circadian mechanisms that interact in complex ways. These relationships have been formalized in electrophysiological, neurochemical and neuroendocrinological models that extend to the pathophysiology of affective illness. Sleep research as a pathophysiological window to the brain has contributed extensively to the understanding of the neurobiology of depression and has been a substantial guide for the advancement of model-driven clinical and preclinical research. Pharmacological probes of normal and depressed sleep play an important role. It is anticipated that the combination of novel topographical EEG and neuroimaging techniques with traditional experimental methods will provide us with further insight into the neurobiology of sleep and depression.