ABSTRACT
OBJECTIVE: Bipolar disorder patients often show excessive goal-directed and pleasure-seeking behavior during manic episodes and reduced hedonic capacity during depressive episodes, indicating that bipolar disorder might involve altered reward processing. As such, bipolar disorder subjects have been reported to show impaired reward learning in situations requiring integration of reinforcements over time. In this study, we examined characteristics of reward learning in euthymic patients with bipolar disorder using a probabilistic reward task. METHODS: We recruited 23 euthymic patients with bipolar disorder and 47 healthy subjects for the probabilistic reward task. This task is a reward-based paradigm to produce a response bias, in which correct identifications of two ambiguous stimuli are differently rewarded. The other dependent measures were the discriminability, hit rate and reaction time. RESULTS: Relative to comparison subjects, bipolar patients showed a reduced acquisition of response bias toward the more frequently rewarded stimulus (p<0.01). The overall reward learning was positively correlated with state and trait anxiety levels in bipolar patients (p<0.01). No significant differences of discriminability, hit rates, and reaction time were found between bipolar patients and controls. CONCLUSION: These findings suggest that euthymic patients with bipolar disorder may have deficits in reward learning related to anxiety.