Sleep Neurophysiology in Depression

Sleep disturbances are both a primary symptom of and risk factor for major depressive disorder (MDD). Sleep alterations in MDD include the presence of insomnia or hypersomnia and aberrations in sleep macro- and microstructure, including a reduced latency until and prolonged duration of the first rapid eye movement (REM) episode, decreased slow-wave sleep (SWS), disturbed sleep continuity and decreased steepening of aperiodic neural activity. MDD sleep is further characterized by dysfunctional autonomic cardiac activity as reflected by decreased heart rate variability. Sedating and novel antidepressants might improve sleep continuity and SWS while activating antidepressants tend to suppress REM sleep. Cognitive processing during sleep may contribute to MDD symptomatology, however empirical research in this direction is still inconclusive. The rapid effects of antidepressants on sleep structure and of acute sleep deprivation on MDD symptoms suggest an intimate association between sleep and MDD neuropathology, however, the underlying mechanisms still need to be elucidated. This narrative review aims to provide a comprehensive overview of our current understanding of the physiology of sleep alterations in MDD and to discuss how sleep may play a role in current therapeutic approaches while also identifying novel strategies for modulating sleep in the context of depression. It seeks to offer a well-rounded foundation of the current knowledge on sleep and depression, meant for basic and clinical scientists to guide future investigations to improve existing and develop novel sleep-based therapeutic interventions.