Characterizing change in vagal tone during the first three years of life: A systematic review and empirical examination across two longitudinal samples

Functioning of the parasympathetic nervous system (PNS), most often indexed by respiratory sinus arrhythmia (RSA), influences the volitional, cognitively-mediated forms of self-regulation across development. However, despite its clear relevance to children's self-regulation, and its utility as a transdiagnostic biomarker of emotion dysregulation and psychopathology, the ontogeny of vagal tone under conditions of homeostasis across infancy and early childhood is not well understood. The current research is comprised of two complementary studies. The first aims to address this gap by conducting a systematic review of the literature which has assessed resting RSA in the first three years of life. The second study uses data from two diverse, longitudinal datasets (n = 203 and n = 370) to model change in RSA from infancy to toddlerhood. Results from a systematic review of 62 studies meeting inclusion criteria suggest that measures of resting RSA increase over time and demonstrate moderate stability across infancy, toddlerhood, and preschool ages. Results from a series of models fit to longitudinal data in study two suggest that baseline RSA is characterized by stable increases across infancy and early childhood. Moreover, although there was equivocal evidence for individual variability in trajectories of RSA, the findings suggest that the individual differences in resting RSA may become entrenched in early life based on observed significant variance in growth model intercepts. In all, the current study contributes to our understanding of the developmental trajectories of baseline RSA across infancy and early childhood and should support future research examining links between children's parasympathetic regulation and their adjustment in early life.

A Developmental Hierarchical-Integrative Perspective on the Emergence of Self-Regulation: A Replication and Extension

This study replicated and extended the Feldman (2009) study by applying the developmental hierarchical-integrative model to understand the emergence of self-regulation. Participants included 360 children (48.6% boys; 62.8% identified as Caucasian and 36.9% African American) and their families, predominantly from a low-income, rural background. Families completed assessments on child physiological, attention, emotion, and self-regulation when children were 6-, 15-, 24-, and 36-month-old, when caregiver sensitivity was observationally assessed. A path model revealed that child attention regulation at 6 months predicted physiological regulation at 15 months, and child attention regulation at 15 months predicted emotion regulation at 24 months. Attention regulation at 24 months predicted better self-regulation at 36 months. Notably, caregiver sensitivity moderated several developmental pathways. Findings support a continuous model of early self-regulation development and the ongoing individual-environment interplay in early childhood.