The ontogeny of autonomic measures in 6‐ and 12‐month‐old infants

The purpose of this study was to develop a standardized protocol to measure preejection period (PEP), a measure of sympathetic nervous system, and respiratory sinus arrhythmia (RSA), a measure of parasympathetic nervous system, during resting and challenging states for 6‐ and 12‐month‐old infants and to determine developmental changes and individual stability of these measures. A 7‐min reactivity protocol was administered to Latino infants at 6 months ( n  = 194) and 12 months ( n  = 181). Results showed: (1) it is feasible to measure PEP and RSA in infants, (2) the protocol elicited significant autonomic changes, (3) individual resting autonomic measures were moderately stable from 6 to 12 months, but reactivity measures were not stable, and (4) heart rate and RSA resting and challenge group means changed significantly from 6 to 12 months. Findings suggest that although infants' autonomic responses show developmental changes, individuals' rank order is stable from 6 to 12 months of age. © 2006 Wiley Periodicals, Inc. Dev Psyshobiol 48: 197–208, 2006.