Physiological Regulation in Young Children During Parent–Child Free Play: Attachment-Related Differences and RMSSD Synchrony

This study examined parent–child physiological synchrony within the context of interactions and attachment-related differences. Specifically, this study investigated physiological synchrony, as indexed by the association between parent and child root mean square of successive differences (RMSSD) during free-play interactions, and differences in children’s mean heart rates according to attachment classification. The participants were 25 parent–child dyads (mean child age = 36.48 months). Physiological responses were assessed during free-play interactions using heart rate (HR) and heart rate variability (HRV). Children’s attachment was classified as secure or resistant based on their behaviors observed during the separation–reunion procedure. The results showed a significant positive association between the parent and child RMSSD (ρ = 0.48, p < 0.05). Parental anxiety was positively associated with both parents’ and children’s physiological arousal. Attachment-related group differences were observed only in the mean heart rate, with children with resistant attachment showing a significantly higher HR than those with secure attachment (t = 2.69, p < 0.05). No significant group differences were observed in the RMSSD or HR/RMSSD ratios. Overall, these findings suggest that the parent–child RMSSD association, as a component of physiological synchrony, may reflect a normative feature of parent–child interaction that emerges across attachment classifications. In addition, attachment-related differences were primarily observed in physiological arousal.