Respiratory sinus arrhythmia and prosociality in childhood: Evidence for a quadratic effect.

Research investigating the link between the parasympathetic nervous system (PNS) and prosociality in childhood has yielded inconsistent findings. This relation has mainly been conceptualized as linear, however, the broader physiological literature suggests that children's physiological arousal and task performance may be related in an inverted U-shaped fashion-with peak performance at moderate levels of arousal. Therefore, we tested whether resting respiratory sinus arrhythmia (RSA)-a dispositional indicator of PNS activity-was quadratically related to child- and caregiver-reported sympathy and prosocial behaviors in an ethnically diverse sample of 4- and 8-year-olds (N = 300). We found a quadratic inverted U-shaped association between resting RSA and child-reported sympathy and prosocial behavior in 8-year-olds, whereas no consistent findings emerged for 4-year-olds. Therefore, moderate resting RSA in middle childhood may facilitate sympathy and prosocial behaviors. Dispositional over- or under-arousal of the PNS may impair children's ability to attend and respond to the distress of others by middle childhood.