17690
Mother Recognition and Preference after Neonatal Amygdala Lesions in Rhesus Macaques (Macaca mulatta) Raised in a Semi-Naturalistic Environment
Attachment to the caregiver, typically the biological mother, is crucial to young mammals’ socio-emotional and cognitive development and its disruption leads to long-term negative outcomes. Although studies in nonprimate species suggest that the amygdala regulates social preference and attachment development, its role in primate filial attachment development has been little investigated and has produced mixed results. In addition, in none of the earlier studies conducted in nonhuman primates (rhesus monkeys) did the mother-infant pairs live in large social environment characteristic of rhesus monkey societies.
Objectives:
This study aimed to assess the specific contribution of the amygdala in the development of filial attachment in primates. We specifically explored the effects of selective bilateral neonatal lesions of the amygdala or sham-operation on the expression of a preference for the biological mother, as well as proximity and comfort-seeking behaviors toward the mother, as compared to another familiar adult female, in infant monkeys raised in a species-typical social environment.
Methods:
Twenty-eight male and female infant rhesus macaques (Macaca mulatta) reared by their mother in complex social groups of about 100 animals underwent selective bilateral lesion of the amygdala (Neo-A, N = 16) or sham-operation (Neo-C, N = 12) at 2-3 weeks of age. Animals were given a preference test (mother vs. familiar female) at 3 and 6 months of age in an experimental, but familiar, environment allowing manual contact with the stimuli.
Results:
Neonatal amygdalectomy did not affect social discriminative abilities and mother preference at 3- and 6-month-old. Nevertheless, as compared to sham-operated controls, amygdalectomized infants were less often in physical contact with their mother across the two testing ages, sought less often proximity with their mother at 3 months as well as reached less often for their mother while in proximity at 6 months.
Conclusions:
These data strongly suggest that the amygdala is not involved in the cognitive processes underlying recognition of and preference for the mother in primates. However, there is still the possibility of an involvement of the amygdala during the formation of the mother-infant bond during the first few postnatal weeks. The findings also indicate that the amygdala might be critical in the development of higher cognitive processes necessary for the maintenance of social relationships and/or the establishment of new ones later on, since the amygdalectomized animals displayed less physical contacts with their mothers. The findings are discussed in relation to the known contribution of the amygdala to filial attachment in both rodents and humans.