The effects of maternal maltreatment on the behavioral and neuroendocrine development of the rhesus macaque (Macaca mulatta) infant: the first six months
McCormack, Kai Marie
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Across many species, early adverse experiences can alter the social and physiological development of individuals. The quality of the early caregiver-infant relationship can serve as a major source of vulnerability in later life. Evidence suggests that the hypothalamic-pituitary-adrenal (HPA) axis may be one system particularly vulnerable to the effects of early post-natal experience. Post-natal experiences can also impact early and later psychological development. This study examined the behavioral and neuroendocrine development of 10 maternally maltreated and 10 control rhesus macaques during the first six months of life. Mother-infant pairs were focally observed every week in captive groups at the Yerkes Field Station. In addition, reactivity ratings were also collected during times of stress. To obtain cortisol measures, basal blood samples were collected monthly, as well as blood samples following mother-infant separations during months 3 and 6. Compared to control infants, maltreated infants broke contact with their mothers less often, and they screamed more and exhibited more tantrums. Abusive mothers broke contact and rejected their infants more frequently than non- abusive mothers. Abused infants did not differ from control infants in their interactions with others. During the first month, when abuse rates were highest, abused infants had elevated levels of basal a.m. cortisol, in comparison to control infants. After the first month, however, they consistently exhibited lower basal and post-separation levels of cortisol compared to the control group. During stressful procedures, abused infants were less likely to be on their mothers, and they were less reactive to being handled. The data suggest that abused infants received lower quality care from their mothers, and that this impacted their cortisol levels. The lower levels of cortisol after month 1 are congruent with the reactivity data, suggesting that the behavioral and physiological systems of the abused infants may have become hypo-responsive in response to early adversity, thereby exhibiting blunted behavioral and cortisol responses. This suggests that rhesus monkeys exposed to early adversity may exhibit outcomes similar to those of maltreated humans, and that their neuroendocrine development may look similar to that of individuals with psychological disorders.