The Longitudinal Role of Mother–Child Synchrony in Predicting Functional Connectivity in Early Childhood

Early childhood is a sensitive period for brain development, during which sustained caregiving experiences may shape neural systems that support emotion regulation and social cognition. In a longitudinal study of N = 133 mother-child dyads, we examined whether children's attachment-related behavioral patterns at age 3 were associated with functional connectivity during the viewing of attachment-related video clips. We further tested whether mother-child behavioral synchrony observed at ages 1 and 3 predicted children's functional connectivity. Neural activity was measured using functional near-infrared spectroscopy (fNIRS), targeting the prefrontal cortex (PFC), and temporoparietal junction (TPJ). Attachment-related behaviors were assessed through a structured observational procedure and rated using the Brief Attachment Screening Questionnaire (BASQ), and mother-child synchrony was coded using the Dyadic Interaction Coding (DIC) system. Children in the BASQ-derived insecure group exhibited greater intra-hemispheric connectivity, whereas those in secure group showed stronger inter-hemispheric connectivity. Mother-child synchrony at ages 1 and 3 did not independently predict later neural connectivity. Instead, mother-child synchrony at age 3 moderated the association between synchrony at age 1 and connectivity at age 3: synchrony at age 1 predicted reduced intra-hemispheric MTG connectivity only when synchrony at age 3 was high. These findings suggest that sustained mother-child synchrony may contribute to the functional organization of neural systems supporting attachment-related processing.