D. Riemann, Department of Clinical Psychology and Psychophysiology, Centre for Mental Disorders, University Medical Centre Freiburg, Germany.

The investigation of sleep in mental disorders has been a focus of neurobiologically oriented sleep research for more than five decades. Based on a meta-analysis of the polysomnographic literature it was confirmed that changes of sleep continuity, and to a lesser extent, sleep depth, are not specific for any mental disorder but occur transdiagnostic. In contrast, changes of REM sleep, like shortened REM latency or increased REM density are more specific for depressive disorders. Interestingly, changes of sleep continuity like prolonged sleep onset latency or an increased number of nocturnal awakenings also occur independent of mental disorders, then called “insomnia disorder”. Insomnia disorder is a risk factor to develop depression and anxiety disorders. Thus, at present we can argue that the relationship between changes of sleep, either insomnia, reduced sleep depth or altered REM sleep latency are not only typical symptoms of many mental disorders but can also be predictive or even be considered risk factors for mental disorders. This bi-directional relationship merits further investigation, with the aim to enhance our understanding of the etiology/ pathophysiology of mental illness and to improve diagnostic, therapeutic and preventive avenues for these disorders.