“…Optimally, the sympathetic and parasympathetic systems should act in concert such that when sympathetic arousal (measured by HR in this study) increases in response to environmental challenge, there should be a decrease in parasympathetic activity (measured by RSA). This negative change in RSA from baseline to environmental challenge is associated with more optimal state regulation in infancy (DeGangi et al, 1991), decreased behavior problems in preschool-aged children (Porges, Doussard-Roosevelt, Portales, & Greenspan, 1996), and more adaptive behavior during attention and affect eliciting tasks in both preschool and school-aged children (Calkins, 1997;Suess, Porges, & Plude, 1994), and during social approach (Stifter & Corey, 2001). Thus, the measurement of change in RSA from baseline to challenging situations is an important concurrent and predictive index of parasympathetic regulation in infants.…”