Significant interactions in infant operculum regions when exposed to a bilingual environment: a resting-state fNIRS study.

Significance: Understanding the regional functionality during early development has significance across various domains such as developmental disorders. Aim: We aim to investigate the impact of early bilingual exposure on infant brain activity at the age of 4 months and to determine whether differences exist in the activity of specific brain regions between monolingual and bilingual infants in rest. Approach: To reach that aim, we utilize a combination of functional near-infrared spectroscopy and effective connectivity analysis (EC), integrated with our previously proposed graph construction method, importance of channel based on EC (ICEC), to assess neural mechanisms underlying bilingualism in infancy. Importantly, we represent a secondary analysis of a publicly available dataset. Results: Employing group-level analysis techniques, our findings reveal that bilingual experience is associated with anatomically specific rather than widespread alterations in EC. Differences were most pronounced in the superior frontal gyrus, superior temporal gyrus, and opercular regions, with the frontal and temporal cortices primarily acting as sources and the operculum functioning as both sources and sinks. Notably, bilingual infants exhibited a gradual increase in connectivity within the rolandic operculum during rest. Temporal analyses further indicated that early rest was marked by stronger inflow into right frontal-opercular hubs, whereas later rest showed a redistribution toward temporal and opercular regions with increased outflow. Together, these results provide evidence that bilingual exposure reorganizes infant brain connectivity in anatomically specific and temporally dynamic ways. Conclusion: These findings provide novel insights into the neurobiological foundations of early bilingual exposure, highlighting distinct patterns of EC in bilingual infants.