Child and mother cardiac vagal tone: continuity, stability, and concordance across the first 5 years.

In this prospective longitudinal study, vagal tone and heart period were measured at 2 months and at 5 years in children and their mothers to evaluate the development of vagal regulation at rest and during an environmental task. Child baseline vagal tone and heart period were discontinuous; mother baseline vagal tone was discontinuous, but heart period was continuous. Group mean baseline-to-task change in vagal tone and heart period were continuous in both children and mothers. Children reached adult levels of baseline vagal tone by 5 years and did not differ from their mothers in baseline-to-task change in vagal tone or heart period. Baseline vagal tone tended to be stable, but baseline heart period and baseline-to-task change in vagal tone and heart period were unstable in children; both were stable in mothers. Baseline-to-task change in vagal tone showed consistent child-mother concordance. These findings contribute to understanding psychophysiological development, especially the ontogenesis of the vagal system and its regulatory capacity.