Deficits of unconscious emotional processing in patients with major depression: An ERP study

•Depression is associated with negative bias in unconscious emotional processing.•Robust emotion×group interactions were observed in P1, N170 and P3.•Unconscious emotional process in patients has a time course of three-stage deflection.

BackgroundMajor depressive disorder (MDD) is associated with behavioral and neurobiological evidences of negative bias in unconscious emotional processing. However, little is known about the time course of this deficit. The current study aimed to explore the unconscious processing of emotional facial expressions in MDD patients by means of event-related potentials (ERPs).MethodsThe ERP responses to subliminally presented happy/neutral/sad faces were recorded in 26 medication-free patients and 26 healthy controls in a backward masking task. Three ERP components were compared between patients and controls.ResultsDetection accuracy was at chance level for both groups, suggesting that the process was performed in the absence of conscious awareness of the emotional stimuli. Robust emotion×group interactions were observed in P1, N170 and P3. Compared with the neutral faces, 1) the patients showed larger P1 for sad and smaller P1 for happy faces; however, the controls showed a completely inverse P1 pattern; 2) the controls exhibited larger N170 in the happy but not in the sad trials, whereas patients had comparable larger N170 amplitudes in sad and happy trials; 3) although both groups exhibited larger P3 for emotional faces, the patients showed a priority for sad trials while the controls showed a priority for happy trials.ConclusionOur data suggested that negative processing bias exists on the unconscious level in individuals with MDD. The ERP measures indicated that the unconscious emotional processing in MDD patients has a time course of three-stage deflection.