Dysfunctional reward learning in bipolar disorder : an event-related potential study

Abstract

Bipolar disorder is characterized by behavioral changes such as risk taking and increased goal directed activity. These kinds of behaviors may account for the abnormal reward processing in bipolar patients which result from impaired reward learning. Bipolar patients have been reported to show impaired reward learning in situations that require integration of feedbacks over time. In this study, I examine the reward learning in manic and euthymic patients with bipolar disorder behaviorally and electrophysiologically using a probabilistic reward task. I recruited 24 manic, 20 euthymic patients with bipolar disorder, and 24 healthy controls. They were required to perform the probabilistic reward task. This task is a reward-based paradigm to produce a response bias, in which correct identification of two ambiguous stimuli is rewarded differently. As a result, both manic and euthymic patients with bipolar disorder showed a reduced acquisition of the response bias toward rich rewarded stimuli (F = 6.21, p = 0.005) and showed attenuated feedback-related negativity in the early phase of the task (F = 6.53, p = 0.003) compared to controls. With the Young’s Mania Rating Scale, positive correlation was shown with the changes of the response bias (p = 0.05) and negative correlation was seen with the changes of feedback-related negativity (p = 0.001). Conclusively, these findings suggest that manic and euthymic patients with bipolar disorder may have deficits in reward learning. Risk taking behavior and reward processing in bipolar patients may be linked to this deficit.