The effects of bilateral lesions of the amygdala on dyadic social interactions in rhesus monkeys (Macaca mulatta)

The role of the amygdala in dyadic social interactions of adult rhesus monk eys (Macaca mulatta) was assessed after bilateral ibotenic acid lesions, So cial, nonsocial, and spatial behaviors of amygdalectomized and control monk eys were assessed in 3 dyadic experiments: constrained, unconstrained, and round robin. Lesions produced extensive bilateral damage to the amygdala. A cross all experiments, the amygdalectomized monkeys demonstrated increased social affiliation, decreased anxiety, and increased confidence compared wi th control monkeys, particularly during early encounters. Normal subjects a lso demonstrated increased social affiliation toward the amygdalectomized s ubjects. These results indicate that amygdala lesions in adult monkeys lead to a decrease in the species-normal reluctance to immediately engage a nov el conspecific in social behavior, The altered behavior of the amygdalectom ized monkeys may have induced the increased social interactions from their normal companions. This is contrary to the idea that amygdalectomy produces a decrease in social interaction and increased aggression from conspecific s.