REM sleep microarchitecture in adolescent major depressive disorder.

Rapid eye movement (REM) sleep abnormalities in adolescents with major depressive disorder (MDD) remain poorly characterized. Although previous work has reported altered eye-movement density and burst dynamics, findings are inconsistent, and few studies have examined the distinct phasic and tonic microstates of REM sleep, each defined by unique neurophysiological signatures. Here, we investigated REM microarchitecture and its association with depressive symptom change using a sleep delay challenge (SDC), an experimental paradigm that delays bedtime by three hours while maintaining total sleep time. This manipulation extends REM sleep duration and shortens REM sleep latency, providing a controlled framework to assess REM regulation. Adolescents with MDD (n = 66) and healthy controls (n = 62) underwent polysomnography across three nights: adaptation, baseline, and SDC. MDD participants exhibited longer phasic REM duration but reduced burst intensity and density relative to controls, along with higher tonic eye-movement density. Only the MDD group showed SDC-related increases in theta-alpha activity time-locked to eye movements over frontal and parietal sites. Within the MDD group, shorter phasic REM duration, higher burst intensity, and lower tonic eye-movement density predicted greater improvement in depressive symptoms following the SDC. These findings suggest that REM microarchitecture, marked by shorter, more intense phasic bursts and reduced tonic eye-movement activity, underlies individual variability in the short-term change in depressive symptom severity response to sleep delay.