Oxytocin administration alters HPA reactivity in the context of parent-infant interaction.

The neuropeptide oxytocin (OT) and the steroid cortisol (CT) have each been implicated in complex social behavior, including parenting, and one mechanism by which OT is thought to exert its pro-social effects is by attenuating hypothalamic-pituitary-adrenal (HPA) response to stress. Yet, no study to date has tested whether OT functions to reduce CT production in the context of the parent-infant attachment. In the current study, we examined the effects of intranasal OT administered to the parent on parent's and infant's CT levels following parent-child interaction that included a social stressor. Utilizing a double-blind, placebo-controlled, within-subject design, 35 fathers and their 5-month-old infants were observed in a face-to-face-still-face paradigm twice, one week apart. Interactions were micro-coded for social synchrony, and salivary CT were repeatedly assessed from parent and child. Results showed that OT increased fathers' overall CT response to the stress paradigm. Furthermore, OT altered infants' physiological and behavioral response as a function of parent-infant synchrony. Among infants experiencing high parent-infant synchrony, OT elevated infant HPA reactivity and increased infant social gaze to the father while father maintained a still-face. On the other hand, among infants experiencing low social synchrony, parental OT reduced the infant's stress response and diminished social gaze toward the unavailable father. Results are consistent with the "social salience" hypothesis and highlight that OT effects on human social functioning are not uniform and depend on the individual's attachment history and social skills. Our findings call to further investigate the effects of OT administration within developmental contexts, particularly the parent-infant relationship.