Parental speech and gesture scaffolding moderate the neural dynamics of parent-child synchrony.

Parent-child interactions foster children's neurocognitive development through multiple pathways. A key pathway involves parental scaffolding, in which parents use speech, gesture, or their combination multimodally to guide children's problem solving and learning. However, the neural processes underlying different scaffolding modalities remain largely unknown. In the present study, we examined the neural basis for the role of parental scaffolding during a parent-child cooperative spatial problem-solving task. We characterized three different types of scaffolds parents used, specifically speech, gesture, and multimodal (speech + gesture). Using an fNIRS-based hyperscanning, we simultaneously recorded neural activity from both members of the dyad. The results revealed parental scaffolding modalities were differentially related to the temporal and spatial structure of neural synchrony. Temporally, multimodal scaffolding (speech combined with gesture) was associated with the most sustained neural synchrony across the interaction, showing the flattest trajectory and the highest level of synchrony, particularly in the later stages. Speech-only scaffolding was associated with an attenuated decline, following a pronounced U-shape with strong late-interaction recovery from a lower baseline. Gesture alone was not reliably associated with attenuation of the decline observed under no scaffolding. Spatially, exploratory channel-based analyses indicated that channel pairs coupling child right dorsolateral prefrontal cortex and parental temporo-parietal areas showed greater synchronization under multimodal scaffolding than other areas. These findings characterize distinct temporal and spatial neural correlates of parental scaffolding modalities. Overall, this study advances our understanding of how parental scaffolding relates to the neural dynamics that support children's engagement during naturalistic cooperative interactions.