DEPRESSION AND SLEEP - PRESENT STATE OF R ESEARCH

Abnormalities of REM sleep, i.e. shortening of REM latency, lengthenin g of the duration of the first REM period and heightening of REM densi ty, which are frequently observed in patients with a Major Depressive Disorder (MDD), have attracted considerable interest. Initial hopes th at these aberrant patterns of sleep constitute specific markers for th e primary/endogenous subtype of depression have not been fulfilled. Th e specificity of REM sleep disinhibition for depression in comparison to other psychopathological groups is also challenged. Demographic var iables like age and sex exert strong influences on sleep physiology an d must be controlled when searching for specific markers of depressed sleep. It is still an open question whether abnormalities of sleep are statemarkers or trait-markers of depression. Beyond baseline studies, the cholinergic REM induction test (CRIT) indicated a heightened resp onsitivity of the REM sleep system to cholinergic challenge in depress ion compared with healthy controls and other psychopathological groups , with the exception of schizophrenia. A special role for REM sleep in depression is supported by the well known REM sleep suppressing effec t of most antidepressants. The antidepressant effect of selective REM deprivation by awakenings stresses the importance of mechanisms involv ed in REM sleep regulation for the understanding of the pathophysiolog y of depressive disorders. The positive effect of total sleep deprivat ion on depressive mood which can be reversed by daytime naps, furtherm ore emphasizes relationships between sleep and depression. Experimenta l evidence as described above instigated several theories like the REM deprivation hypothesis, the 2-process model and the reciprocal intera ction model of nonREM-REM sleep regulation to explain the deviant slee p pattern of depression. The different models will be discussed with r eference to empirical data gathered in the field.