Emotional responses in monkeys differ depending on the stimulus type, sex, and neonatal amygdala lesion status

The amygdala plays an essential role in evaluating social information, threat detection, and learning fear associations. Yet, most of that knowledge comes from studies in adult humans and animals with a fully developed amygdala. Given the considerable protracted postnatal development of the amygdala, it is important to understand how early damage to this structure may impact the long-term development of behavior. The current study examined behavioral responses toward social, innate, or learned aversive stimuli among neonatal amygdala lesion (Neo-Aibo; males = 3, females = 3) or sham-operated control (Neo-C; males = 3, females = 4) rhesus macaques. Compared with controls, Neo-Aibo animals exhibited less emotional reactivity toward aversive objects, including faster retrieval of food reward, fewer fearful responses, and more manipulation of objects. This lower reactivity was only seen in response to social and innate aversive stimuli, whereas Neo-Aibo animals had similar responses to controls for learned aversive stimuli. The current study also detected sex differences in behavioral response to aversive stimuli, such that, as compared with males, females took longer to retrieve the food reward across all aversive stimuli types, but only expressed more hostility and more coo vocalizations during learned aversive trials. Early amygdala damage impacted the expression of some, but not all, sex differences. For example, neonatal amygdala damage eliminated the sex difference in object manipulation. These findings add important information that broaden our understanding of the role of the amygdala in the expression of sexually dimorphic behaviors, as well as its role in learning fear associations and threat detection. (PsycINFO Database Record (c) 2020 APA, all rights reserved).