Reward mechanism of depressive episodes in bipolar disorder: Enhanced theta power in feedback-related negativity

• Patients with bipolar disorder (BD) depression did report anhedonia in everyday life. • A deepened feedback-related negativity (FRN) in response to negative outcomes was observed in the classic gambling paradigm in BD depression. • The FRN was composed by increased theta power. This study aimed to explore the reward-related neural mechanism in patients with depressive mood in bipolar disorder (BD) using event-related potentials. It remains unknown whether or not different neurobiological markers underlying depression symptoms in BD depression and major depression disorder (MDD). 24 patients with BD depression and 20 healthy controls were included. Participants underwent evaluation with the Temporal Experience of Pleasure Scale (TEPS), followed by the classical gambling paradigm, while undergoing 64-channel electroencephalography. The waveform of feedback-related negativity (FRN) was extracted from the 250–350 ms time-window after participants received feedback regarding loss or gain. Event-related potential datasets were obtained using time-frequency analysis. (1) The TEPS scores of the patients were significantly lower than those of the controls [ t (42) = 5.16, p < 0.01]. (2) The event of loss elicited a deeper FRN in patients than that in controls [ t (42) = 2.19, p < 0.05], while no difference was observed in the event of gains ( t (42) = 1.12, p > 0.05). (3) Theta power rooted in FRN in patients was significantly higher in loss than in gain [ F (1,42) = 30.32, p < 0.01]. (4) Analysis of Variance (ANOVA) illustrated the interaction effect of theta power in gain/loss between two groups [ F (1,42) = 3.59, p = 0.06]. Our study did not analyze the effect of different drugs which might affect our results. The enhanced reflection of negative feedback was consistent with the negative bias, impulse control impairment, and emotional dysregulation observed in the bipolar disorder spectrum. We suggested that the extreme theta power generated from the anterior cingulate gyrus (ACC) might be the main component of abnormal FRN.