Relationship between oxytocin and maternal approach behaviors to infants' vocalizations.

Infants communicate their emotions to caregivers mainly through vocalizations. Research has shown that maternal oxytocin levels relate to adaptive parenting; however, little empirical research exists regarding the effects of endogenous oxytocin levels on maternal responses to infant vocalizations. Thus, in this study, we examined the relationship between mothers' salivary oxytocin levels, subjective feelings, and behavioral response to infants' emotional vocalizations. Additionally, we examined the relationship between psychological traits and maternal behavioral responses to infant vocalizations. In this study, 39 mothers were asked to stand on a balance board while listening to infant vocalization stimuli, to measure movements of their center of pressure, an index of approach-avoidance behavior. Sixty infant vocalizations (laughter, crying, and neutral) were presented for 6 ​s each. Afterwards, participants were asked to rate their subjective responses to each stimulus (not aroused - aroused, displeased - pleased, not urgent - urgent, and healthy - sick). Maternal oxytocin levels were negatively correlated with anterior movement of the center of pressure in response to infants' crying and babbling vocalizations, though no relationship was found between maternal approach-avoidance behavior toward infant laughter and oxytocin levels. This study indicated that maternal approach behavior toward infant vocalizations varies as a function of maternal endogenous oxytocin and the type of infant vocalization.