Infants' Biological Sensitivity to the Effects of Maternal Social Support: Evidence Among Mexican American Families.

The identification of infants who are most susceptible to both negative and positive social environments is critical for understanding early behavioral development. This study longitudinally assessed the interactive effects of infant vagal tone (respiratory sinus arrhythmia; RSA) and maternal social support on behavioral problems and competence among 322 low-income Mexican American mother-infant dyads (infants: 54.1% female) and explored sex differences. Infant RSA was calculated from resting HR data at 6 weeks of age. Mothers reported on general social support, partner support, and family support at 6 months, and infant behavioral problems and competence at 1 year. Two-way interactions (RSA × support source) were evaluated to predict behavioral problems and competence, adjusting for covariates. Results indicated higher competence among infants with lower RSA whose mothers reported higher general support or higher partner support. Interactive effects on behavior problems of RSA with maternal partner or family support were only found for female infants: Girls with higher RSA showed more behavior problems when mothers reported low support, but fewer problem levels in the context of high support. Our results suggest that infant RSA is an important moderator of the effects of the early social environment on early development.