Influence of amygdalectomy on social behavior in monkeys.

Abstract

Eight young male rhesus monkeys were studied in individual and group cages for a period of 9 mos.; during this time, the 3 animals that were most dominant in the group situation were subjected to bilateral amygdalectomy. There was found to be a negative relationship between aggressiveness in the individual-cage and dominance in the group-cage situation before surgery. After amygdalectomy all animals appeared more aggressive in the individaul-cage situation. In the group-cage situation, the same animals, in 2 of 3 instances, fell from top to bottom positions in the hierarchy. The 3d animal suffered no loss in dominance and appeared more aggressive in the group situation after operation. The differences in changes in behavior appeared to be related to the social environment confronting each animal upon returnrto the group after surgery and to the length of time the preoperative relationships had existed. The differences in changes in behavior are not related to the differences in extent of lesions as a whole, though they are consistent with differences in damage to the basolateral nuclei of the amygdala.