Background: This study examines the directionality and temporal specificity of brain activity during sustained processing of emotional stimuli in individuals with current major depressive disorder (MDD) and nondepressed control participants.
Methods: Slow wave (SW) components of the event-related brain potential (ERP) were recorded from 16 control participants and 15 participants with MDD during a working memory task. During the task, individuals were shown a positive, neutral, or negative word and were asked to maintain it in memory for 5 sec. Participants then saw a letter and had to decide whether it was a part of the previously presented word. The ERP components were measured from nine scalp sites (F3, Fz, F4, C3, Cz, C4, P3, Pz, P4) during the encoding of emotional words.
Results: Compared with control individuals, MDD participants exhibited decreased brain responses to positive relative to negative or neutral stimuli. This decrease in brain activity during processing of positive information was evident across all sites and SW components.
Conclusions: Our findings suggest that cognitive deficits in MDD may stem from diminished brain responses during processing of positive information and may not be associated with an augmented response to negative stimuli.