A shift in brain functional systems during mother-child neural synchrony marks children's cognitive development.

Mother-child social interaction plays a crucial role in shaping children's cognitive development over the preschool years, with a particular emphasis on their self-regulation ability. Despite this acknowledged importance, the specific elements within mother-child interaction that significantly contribute to the development of children's self-regulation ability remain elusive. Additionally, the neural underpinnings associated with diverse facets of mother-child interaction have yet to be fully elucidated. To address these issues, this study integrated age-appropriate free-play tasks with the functional near-infrared spectroscopy (fNIRS) hyperscanning technique. The sample included 24 mother-child dyads and 24 stranger-child dyads in the 3-year-old group, and 25 mother-child dyads and 25 stranger-child dyads in the 7-year-old group. The results showed that behaviorally, committed compliance that reflects children's self-regulation ability was the dominant behavioral pattern among both age groups. At the neural level, interpersonal neural synchronization between the temporoparietal junction (TPJ) of children and inferior frontal cortex (IFC) of mothers was significantly associated with the committed compliance in the 3-year-old group. Conversely, in the 7-year-old group, a significant correlation was observed in the INS between the TPJ of mothers and that of children. Further analysis indicated that, at the age of 3, mutual responsiveness contributed more to children's self-regulation ability, and this effect was mediated by the TPJ-IFC's INS. In contrast, at the age of 7, children's responsiveness had a greater impact, which was mediated by the TPJ-TPJ's INS. Collectively, these results suggested a shift in neural functional systems supporting different aspects of mother-child interactions throughout the preschool period, thereby significantly contributing to children's self-regulation development.