Distinct temporal neural dynamics of working memory in depressive patients: early encoding deficits and late maintenance correlates of rumination.

Working memory (WM) deficits and maladaptive rumination are hallmark features of major depressive disorder (MDD), yet the stage-specific electrophysiological mechanisms remain poorly understood. This study investigated neural dynamics during WM encoding and maintenance in individuals with depressive episode (DE) and their associations with rumination subfactors. A total of 59 DEs and 49 healthy controls (HCs) performed an n-back task (0-back and 2-back) while 64-channel electroencephalography (EEG) was recorded. Behavioral results demonstrated that the DEs exhibited impaired WM updating, characterized by significantly lower accuracy and slower reaction time (RT) under high cognitive load. Electrophysiological analyses revealed that during encoding, the DEs showed attenuated load-related modulation of the frontal N2 amplitude. During maintenance, the DEs demonstrated pathologically elevated occipital alpha power. Crucially, a significant group × alpha interaction (Wald χ² (1) = 9.258, p = 0.002) in predicting RT was observed. Higher alpha power was associated with slower RT in HCs (β = 0.006, p = 0.021), whereas this neurobehavioral coupling was disrupted and paradoxically reversed in the DEs (β = -0.003, p = 0.063). Within the DE group, alpha power was significantly negatively associated with brooding (β = -0.962, p = 0.006) and reflective pondering (β = -0.692, p = 0.035) independent of task load. Our findings reveal that impaired resource mobilization during encoding and disorganized functional inhibition during maintenance converge to drive WM deficits in depressive patients, with the latter uniquely tied to maladaptive rumination.