Early amygdala or hippocampus damage influences adolescent female social behavior during group formation

This study continues a longitudinal analysis of rhesus macaque social behavior following bilateral neonatal ibotenic acid lesions of the amygdala or hippocampus, or sham operations. The social behavior of female subjects was evaluated at a critical developmental time point—the transition to adulthood. At approximately 4 years of age, female subjects were housed in small groups with other female subjects and reproductively viable adult males. As compared to neurologically intact control animals and animals with early amygdala damage, animals with early hippocampal damage were more social with their female peers. In contrast, as compared to control animals, animals with early amygdala damage spent less time with the males, engaged less frequently in behaviors typical of reproductive consortships, had higher frequencies of self-directed stereotypies, and became pregnant later. Males also generated fewer communicative signals towards animals with early amygdala damage than to control animals and animals with early hippocampus damage. Rates of sexual behavior were generally low for all animals and there were no lesion-based differences in their frequencies. Discriminant function analyses demonstrated that patterns of affiliative social behaviors differed across the three experimental groups, both in terms of the social behaviors directed to the males, and the social behaviors generated by the males towards the females. In four of the five social groups, amygdala-lesioned animals were lowest ranked, potentially contributing to reduced sociability interactions with males. Other potential mechanisms and the experiments needed to elucidate them are discussed.