Lay summary
The recruitment process of this study was very demanding. We required 3 years to carefully recruit 17 young depressed women who were unmediated and willing to participate in a challenging laboratory protocol, which lasted 64 hours during which intensive physiological and psychological monitoring was performed. Careful screening enabled us to really assess whether potential volunteers suffered from a major depression but not from insomnia. This was confirmed by significant lower self-ratings of their mood, standardized depression scales by external psychologist and polysmonographic sleep screenings during an adaptation night in the laboratory.Inspection and first analysis of the data indicate that unmediated young depressive women without sleep problems live under a higher sleep pressure than an age-matched healthy female control cohort. This was quantified by increased levels of low EEG components during wakefulness, baseline sleep and recovery sleep after high- and low sleep pressure challenges as well as increased levels of subjective sleepiness and subjective tension in the depressed women compared to the controls. Circadian phase and its timing relative to the sleep-wake cycle did not differ between depressed and control women, although night time melatonin secretion was significantly reduced in the depressed cohort.As a first conclusion, we hypothesize that a use-dependent phenomenon (enhanced rumination in depression) and/or attenuated circadian amplitude at night could lead to higher sleepiness levels or more sleep pressure in women suffering depression without sleep problems. In the future it would be interesting to test efficacy of a chronotherapeutic, such as light treatment, in order to counteract higher sleep pressure levels and/or enhance the circadian alerting drive in these depressive women.