Reduced electrocortical responses to pleasant pictures in depression: A brief report on time-domain and time-frequency delta analyses

Background: The late positive potential (LPP) to pleasant content is an electrocortical indicator of blunted emotional reactivity in depression. A reduced time-frequency delta power has never been investigated in clinical samples. The present study examined time-frequency delta in depression and at investigated whether the combination of time-domain and time-frequency data would explain additional variance in the depression status. Methods: The study was a secondary analysis of data collected during a passive viewing task of pleasant and neutral pictures in a community-based sample of 75 participants with a current depressive disorder and 42 controls. A time-frequency analysis on event-related changes within delta frequency band was conducted. Results: Cluster-based statistics revealed a centro-parietal increase in delta power to pleasant relative to neutral pictures in the control group but not within the depression group. Moreover, a fronto-centro-parietal reduction in delta power to pleasant pictures emerged in depression relative to controls. Both a smaller LPP and delta power to pleasant pictures were related to depression status. The combination of LPP and delta power explained a greater amount of variance compared to the model where LPP was entered as the only predictor of depression status. Conclusions: These data suggest that delta power might be a promising electrocortical correlate of the hypo activation of the approach-related motivational system in depression. Additionally, a blunted delta and LPP might reflect unique processes related to depression. A combination of these measures can be leveraged together to enhance clinical utility and to shed light on the underlying mechanisms associated with depression.