During the proposed study functional magnetic resonance images will be acquired while subjects perform a version of the probabilistic reversal learning task. Four groups will take part: MDD, bipolar depressed, unmedicated MDD in remission and healthy control subjects. These images will be used to investigate differences in neural activation between the four groups, to clarify whether this specific profile of behavioral response extends to bipolar depressed subjects and to assess the mood state dependences of this effect. This would increase understanding of the specific profile of performance on this task and neural basis of this abnormal response to negative feedback that contributes to impairment of cognitive performance in depression.