ABSTRACT Respiratory sinus arrhythmia (RSA), an index of physiological regulation, increases during infancy, and is associated with concurrent and later social abilities. However, little is known about the moment‐by‐moment, bidirectional dynamics of RSA and social behaviors. This is particularly relevant to autism spectrum disorder (ASD), in which altered RSA may underly social deficits. The current study investigated the dynamic relationship between RSA and social behaviors in very young infants with and without ASD. Infants ( N = 74) at elevated (EL) or low (LL) familial likelihood for ASD who were later classified as typically developing (TD) or having ASD were included in analyses. These infants completed a dyadic, face‐to‐face interaction with their caregivers at 3, 4, and 6‐months. Infant social behaviors (looking and smiling) and RSA during the interaction were quantified. Granger causality analyses determined if RSA significantly “forecasted” social behaviors and vice versa. Social behavior, especially looking to the caregiver, significantly forecasted moment‐to‐moment changes RSA in more infants than the converse. Smiles forecasted RSA in more EL infants than LL infants. Looks forecasted RSA in more infants with ASD than TD infants. We found a bidirectional relationship between RSA and social behavior, with social behavior more often forecasting RSA. Infants later diagnosed with ASD showed a greater likelihood for social attention to forecast RSA than TD infants, suggesting early differences in dynamic behavior‐physiology processes. Additionally, EL infants showed a greater likelihood for smiling to forecast RSA than LL infants, suggesting that ASD likelihood may influence early physiological and social dynamics, regardless of outcome. Summary We explored the dynamic and bidirectional relationship between social behavior and respiratory sinus arrhythmia (RSA) in infants with and without autism spectrum disorder (ASD). Infant social behavior, especially looking to the parent, significantly forecasted moment‐to‐moment changes in RSA in more infants than the converse. Smiles forecasted RSA in more infants at elevated than low likelihood for ASD, suggesting that ASD likelihood may influence early physiological and social dynamics. Looks forecasted RSA in more infants with ASD than TD infants, suggesting early differences in dynamic behavior‐physiology processes.
Yurkovic‐Harding et al. (Sat,) studied this question.