Dyadic physiological synchrony and maternal anxiety regulate infant autonomic and neural function.

Caregiver-infant physiological synchrony has been proposed as a mechanism through which early caregiving interactions shape regulatory systems and facilitate the transmission of emotional signals within dyads. However, it remains unclear how synchrony interacts with maternal emotional context and developmental timing to influence infant neurophysiological development. Specifically, we examined the effects of maternal anxiety and mother-infant physiological synchrony at 3 months postpartum on infant autonomic regulation and neural function. Infant physiological regulation was indexed by respiratory sinus arrhythmia (RSA), and neural function was indexed by aperiodic EEG slope and theta-beta ratio measured at 3 and 9 months. Surrogate control analyses confirmed that physiological synchrony significantly exceeded chance at 3 months. Further, higher maternal anxiety was associated with lower infant RSA and steeper aperiodic slopes across both timepoints. Developmental timing modulated these associations: anxiety effects on RSA and aperiodic slope were stronger at 9 months, whereas the associations of physiological synchrony with RSA and aperiodic slope were age-dependent, with concurrent effects at 3 months that attenuated by 9 months. Finally, physiological synchrony moderated the effect of maternal anxiety on infant RSA in a context-dependent manner - among high-synchrony dyads, greater anxiety predicted lower RSA, while no such association emerged among low-synchrony dyads. Interestingly, there were no main or interacting effects of synchrony or anxiety on theta-beta ratio. Together, these findings highlight the timing- and context-dependent role of physiological synchrony in shaping infant neural and autonomic development, suggesting that synchrony may both support regulation and intensify the transmission of maternal emotional states.