| The amygdala and orbital prefrontal cortex (PFo) interact as part of a system for affective processing. To assess whether there is a hemispheric functional specialization for the processing of emotion or reward or both in nonhuman primates, rhesus monkeys were prepared with combined lesions of the amygdala and PFo in one hemisphere (left or right) and compared with unoperated controls on a battery of tasks that tax affective processing. Results from five tasks are reported here: (1) reinforcer devaluation; (2) reaction to a rubber snake; (3) object reversal learning; (4) reaction to a human intruder; and (5) response to reward magnitude shifts. For task 1, whereas controls showed robust devaluation effects, as evidenced by their tendency to avoid choosing objects overlying the devalued food, monkeys with unilateral lesions, left or right, showed attenuated reinforcer devaluation effects. For task 2, monkeys were measured on their latencies to reach over a rubber snake to obtain a food reward. On snake trials monkeys with unilateral lesions, left or right, exhibited reduced latencies relative to controls. Latencies to reach over neutral objects did not differ across groups. Monkeys with left or right lesions did not differ from controls in tasks 3, 4, and 5. This study does not provide evidence of hemispheric functional specialization. Reported here, however, is the novel result that unilateral lesions of the amygdala-PFo circuit in monkeys are sufficient to significantly disrupt some aspects of affective processing. This finding could have important implications for the understanding of fear processing and reward-related processing in humans. |
