Background: Sleep plays a critical role in mood regulation, yet the mechanisms linking sleep to mood improvement remain unclear. Electroencephalographic (EEG) slow-wave activity (SWA) during non–rapid eye movement (NREM) sleep is reduced in patients with major depressive disorder. Here, we examined sleep architecture in patients with depression undergoing electroconvulsive therapy (ECT). Methods: Sleep EEG data were collected using wireless Dreem devices before and after each ECT session serially throughout the ECT course. Sleep stages were manually scored into rapid eye movement (REM) and NREM stages (N1–N3) according to modified American Academy of Sleep Medicine guidelines. Depression severity was assessed using the 16-Item Quick Inventory of Depressive Symptomatology-Self Report (QIDS). SWA was quantified as the average 0.5-4 Hz frontal EEG power per minute during N2 and N3 sleep. Results: Across 214 sleep records from 22 subjects (median 9 per patient), the percentage of time in N3 sleep increased over the course of therapy in the responders’ group ( P =0.030). SWA increased throughout the ECT course across all participants ( P =0.001), and it was negatively correlated with the QIDS score ( P <0.001). Mediation analysis revealed that SWA mediated the effect of treatment on QIDS only in the responders’ group ( P =0.037). Conclusion: Our findings demonstrate that ECT increases N3 sleep and SWA in the responders’ group, with SWA changes mediating improvements in depressive symptoms. These findings highlight SWA as a biomarker of antidepressant response and a potential target for sleep-based strategies to augment brain stimulation therapies for depression.
Kafashan et al. (2026) studied this question.