Amygdala and orbitofrontal cortex lesions differentially influence choices during object reversal learning.

In nonhuman primates, interaction between the orbitofrontal cortex (OFC) and the amygdala (AMG) has been seen as critical for learning and subsequently changing associations between stimuli and reinforcement. However, it is still unclear what the precise role of the OFC is in altering these stimulus-reward associations, and recent research has questioned whether the AMG makes an essential contribution at all. To gain a better understanding of the role of these two structures in flexibly associating stimuli with reinforcement, we reanalyzed a set of previously published data from groups of monkeys with either OFC or AMG lesions that had been tested on an object reversal learning task. Based on trial-by-trial analyses of rewarded and unrewarded choices, we report two new findings. First, monkeys with OFC lesions were, compared with both control and AMG groups, unable to use correctly performed trials to optimally guide subsequent choices. Second, monkeys with AMG lesions showed the opposite pattern of behavior. This group benefited more than controls from correctly performed trials that followed an error. Finally, as has been reported by others, after a change in reward contingencies, monkeys with OFC lesions also showed a slightly greater tendency to choose the previously rewarded object. These findings demonstrate that the OFC and AMG make different contributions to object reversal learning not highlighted previously.