Social attachment in juvenile monkeys with neonatal lesion of the hippocampus, amygdala and orbital frontal cortex

Non-human primates, like humans, develop and maintain social relationships and attachments throughout their life. The first and most crucial relationship in a primate life is that with its mother. Yet, in absence of their biological mother, infant primates form attachment to surrogate mothers. Although, this early attachment is critical for the development of normal species-typical social and emotional skills, the neural substrates underlying the formation of social relationships in primates are still unclear. The present study assessed, in infant rhesus monkeys (Macaca mulatta) reared by human caregivers and social interactions with peers, the effects of bilateral neonatal (1-2 weeks of age) ibotenic acid lesions of the amygdala and hippocampus (N = 6 in each group), aspiration lesions of the orbital frontal cortex (N = 6) or sham lesions (N = 5) on the development of a social attachment with the principal human caregiver. A specific preference for the later was assessed at 11 months of age, in a two-choice discrimination task, opposing the principal human caregiver to another familiar human, in a familiar environment. None of the lesions impaired the expression of preferential responses toward the principal human caregiver. Nevertheless, lesions of the orbital frontal cortex led to a weaker preference, suggesting that this structure may play a role in the quality and/or strength of the infant/mother relationships. The present non-human primate findings are discussed in terms of their relevance for autism.