Recent findings indicate that in the first half of the night, individuals with major depressive disorder (MDD) who have less slow-wave activity (SWA) dissipation as a consequence of impaired SWA regulation have greater mood disturbance, and may suggest that appropriate homeostatic regulation of sleep is an important factor in the disorder. 37 depressed and 59 healthy adults spent 3 consecutive nights in a sleep laboratory. On the third night, bedtime was delayed by 3 hours, as this procedure has been shown to provoke SWA. The Profile of Mood States questionnaire was administered on the morning following the baseline and sleep delay nights to measure mood disturbance. Researchers found that following sleep delay, a lower delta sleep ratio, indicative of inadequate dissipation of SWA from the first to the second non-rapid eye movement period, predicted increased mood disturbance in only those with MDD.
Goldschmied JR, Cheng P, Hoffmann R, Boland EM, Deldin PJ, Armitage R. Effects of slow-wave activity on mood disturbance in major depressive disorder. Psychol Med. 2019;49(4):639-645. doi:10.1017/S0033291718001332.
This paper by Goldschmied et al. contributes to the literature that theorizes that depression may either lead to or contribute to disrupted circadian rhythms or brain activity during sleep. Here, in non-depressives, sleep delays allowed dissipation of deep sleep/slow-wave activity where in depressed patients this did not occur. Furthermore, this relative excess in depressives seemed to initiate next day increases in dysphoria. Researchers continue to link abnormal sleep electrophysiologic findings to symptom generation in major depressive disorder. Slow-wave sleep activity is theorized to downgrade synaptic strength. Here, depressed patients may have too much of this activity and lose synaptic plasticity. Other treatments such as certain psychotherapies, pharmacotherapies, and neuromodulation techniques have been shown to increase neurotrophic factors (and plasticity) en route to remitting depressive symptoms. It is interesting also that delaying sleep to a greater degree (or sleep deprivation) may lower slow-wave activity and allow greater plasticity in a parallel model providing not only a biomarker but also a possible treatment for major depressive disorder. —Thomas L. Schwartz, MD; Senior Associate Dean of Education, Interim Chair/Professor of Psychiatry, SUNY Upstate Medical University.