Bilateral neurotoxic amygdala lesions in rhesus monkeys (Macaca mulatta): consistent pattern of behavior across different social contexts.

Although the amygdala has been repeatedly implicated in normal primate social behavior, great variability exists in the specific social and nonsocial behavioral changes observed in nonhuman primates with bilateral amygdala lesions. One plausible explanation pertains to differences in social context. This study measured the social behavior of amygdala-lesioned and unoperated rhesus monkeys (Macaca mulatta) in 2 contexts. Monkeys interacted in 4-member social groups over 32 test days. They were previously assessed in pairs (N. J. Emery et al., 2001) and were therefore familiar with each other at the beginning of this study. Across the 2 contexts, amygdala lesions produced a highly consistent pattern of social behavior. Operated monkeys engaged in more affiliative social interactions with control partners than did controls. In the course of their interactions, amygdala-lesioned monkeys also displayed an earlier decrease in nervous and fearful personality qualities than did controls. The increased exploration and sexual behavior recorded for amygdala-lesioned monkeys in pairs was not found in the 4-member groups. The authors concluded that the amygdala contributes to social inhibition and that this function transcends various social contexts.