Threat perception and behavioral reactivity in response to an acute stressor in infant rhesus macaques.

Attentional bias to threat is an adaptive response to the presence of threat and danger in the environment (Haselton et al., 2009; Pollak, 2008). Attentional bias to threat is present in both human and nonhuman primates (e.g., Mandalaywala, Parker, & Maestripieri, 2014) and attentional bias to threat is exacerbated during periods of acute stress in rhesus macaque adults (Bethell et al., 2012a,b). Here, we build on this extant work to assess whether 5-month-old infant rhesus macaques, previously believed to be too young to express attentional bias to threat, might actually demonstrate attentional bias in response to an acute stressor. At approximately 5 months of age, free-ranging rhesus macaque infants on Cayo Santiago, Puerto Rico (N = 44) were briefly separated from their social group and underwent a maternal separation test, a validated stressor shown to induce anxiety in infant monkeys (Sánchez et al., 2001). We assessed their behavioral (Temperament Task) and cognitive (Threat perception/Vigilance for Threat task) reactivity. Across these two reactivity tests, infants could be classified as "vigilant-fighters"-trying to escape and paying more attention to a threatening than a neutral stimulus-or as "avoidant-freezers"-staying still and quiet and avoiding looking at the threatening stimulus in favor of the neutral stimulus. This behavioral and cognitive phenotype was related to infants' early life experiences, including exposure to early life adversity, and suggests both that attention to threat can be present as young as 5 months of age, and that infants quickly learn behavioral and cognitive strategies for coping with their particular circumstances.