Neural sleep signatures in major depressive disorder: Altered oscillatory and aperiodic components

This study aimed to extend prior work on sleep as a window into the pathophysiology of major depressive disorder (MDD), incorporating recent advances in characterizing oscillatory and non-oscillatory brain activity during non-rapid eye movement (NREM) sleep. We specifically tested the hypotheses of reduced coupling between slow oscillations (SO) and sleep spindles, quantified by the modulation index (MI), and a shift toward excitatory activity, reflected in a flattened spectral slope compared to healthy controls.

Polysomnography/EEG data were analyzed from 14 medication-free patients with MDD (age 38.7 ± 11.4 years) and 14 healthy controls (age 38.8 ± 11.5 years). Both groups showed a predominance of male participants (13 men, 1 woman per group), limiting the assessment of sex-specific effects. SO-spindle coupling was quantified via the modulation index (MI). The aperiodic spectral slope (1-45 Hz) was estimated during NREM and REM sleep.

Patients with MDD exhibited significantly reduced SO-spindle coupling and a flattened spectral slope across NREM and REM sleep compared to controls. MDD patients showed a reduced spindle density. Standard polysomnographic parameters did not differ between the groups in the current sample DISCUSSION: This study provides the first evidence that MDD is characterized by reduced slow oscillation-spindle coupling and a flattened spectral slope during sleep. These alterations suggest attenuated thalamocortical coordination and may represent a mechanistic link between sleep physiology and clinical symptoms.