Caregiver Holding, Not Vocalizing, Supports Real-Time Vagal Regulation

Caregivers play a critical role in infant physiological regulation. Lab-based studies show that more responsive mothers have infants that are better regulators, indexed by a decrease in infant respiratory sinus arrhythmia (RSA) during standardized stressors. However, little is known about the specific caregiving behaviors that lead to physiological regulation. This study leverages wearable sensors and ecologically valid observations of mother and infant behavior to identify how spontaneous caregiving behaviors influence real-time mother and infant parasympathetic regulation following infant distress. N = 41 mother-infant dyads (mean age 4.6 months) were recruited from an urban North American city. Infants and mothers wore ECG monitors while being video recorded participating in daily routines around their home for 1 hour. Trained RAs annotated infant crying and mothers' regulation behaviors, including holding and speaking to their infant. Contrary to laboratory findings, mothers did not respond immediately to their infant's crying in ecologically valid home interactions, with most response latencies around 10 s and some up to 2-3 min. Additionally, not all caregiving behaviors had effects on real-time physiological regulation. Mothers holding their infant, but not vocalizing, produced significant time-locked decreases in real-time mother and infant RSA, corresponding to regulation. Physical touch, but not vocalizations, may scaffold mother and infant physiological regulation in the context of unprompted infant distress. Specific caregiving behaviors actively shape in-the-moment physiological arousal and regulation "in the wild."