State-Dependent qEEG Biomarkers in Depression.

BackgroundsIdentifying state biomarkers in major depressive disorder (MDD) is critical for understanding neurobiological underpinnings of disorder. Quantitative electroencephalography (qEEG) has emerged as a promising tool for distinguishing stable versus dynamic neural alterations associated with MDD.MethodsThis study included 70 patients diagnosed with MDD and 98 healthy controls (HC). Resting-state qEEG recordings were obtained at three time points: baseline(T0), early treatment(T1), and late treatment(T2). Patients were categorized as responders(≥50%HDRS-21) or non-responders. Changes in absolute band power across delta, theta, alpha, beta, and gamma frequencies were compared with HCs. Associations between qEEG activity with HDRS and HARS scores at each time point were calculated.ResultsResponders showed longitudinal reductions in delta power with normalization toward HCs. Gamma activity increased marginally over time. Non-responders exhibited stable and elevated delta and alpha power that persisted across sessions. Decreased fronto-central delta and increased left fronto-central gamma power were also associated with improvement in depression and anxiety.ConclusionMDD Responders demonstrated state-dependent electrophysiological normalization, while non-responders show stable pattern with unchanged depressive state. These findings highlight the utility of qEEG state-markers in monitoring clinical improvement in depression.