Development of mother-infant co-regulation: The role of infant vagal tone and temperament at 6, 9, and 12 months of age.

Using Porges' (2011) Polyvagal Theory as a backdrop, this study examined whether changes in parasympathetic functioning, as indexed by baseline measures of cardiac vagal tone at 6, 9, and 12 months of age, were linked to changes in infants' (N = 101) dyadic co-regulation over these same time points. Mothers and infants were observed at each time point during a 15-minute unstructured free-play and co-regulated patterns of interactions were coded using the Revised Relational Coding System (Fogel et al., 2003). Analyses were carried out using multi-process growth curve modeling to examine baseline measurements (intercepts) and changes (slopes) in vagal tone, co-regulation as well as mothers' report of infant temperament. Findings demonstrate links between infants' vagal tone and changes in mother-infant co-regulation. Specifically, increasing levels of cardiac vagal tone was related to increases in symmetrical but decreases in unilateral patterns of co-regulation over time. These findings suggest that changes in the autonomic nervous system likely undergird infants' improving capacity to engage in more mutually sustained patterns of co-regulation.