Psychoendocrine aspects of mother-infant relationships in nonhuman primates.

Studies will be presented which examine the physiological and behavioral responses of squirrel monkeys and rhesus macaques following disruptions of mother-infant relationships. Reliable increases in circulating levels of plasma cortisol occur following separation of the infant from its mother. The presence of familiar conspecifics during the time of separation reduces the pituitary-adrenal response, compared to that elicited by total isolation. Visual access to the mother during separation also ameliorates the plasma cortisol response. However, when infants are separated in the presence of unfamiliar conspecifics, the physiological response is exaggerated compared to animals which are totally isolated. The behavior expressed by the infant during separation, particularly separation-induced vocalizations, is not concordant with this physiological index of affect. The rate of vocalization produced when the infant has visual access to the mother was higher than when the infant was totally isolated. However, when allowed access to familiar conspecifics, the rate of vocalization was lower than during total isolation, with no vocalization produced while the separated infant was in the unfamiliar social group. The curvilinear relationship between vocalization and the physiological index of arousal has led to a revision of the traditional concept that separation-induced infant vocalization is reflective of distress. These data support the hypothesis that vocalizations may serve as a coping response that reduces the physiological indices of arousal. Social interaction with familiar cospecifics may serve as a non-vocal coping response (e.g., proximity contact to other monkeys) which also reduces the behavioral and physiological responses to maternal separation.