Interactive live fNIRS reveals engagement of the temporoparietal junction in response to social contingency in infants.

Live social interaction is the dominant form of human social activity, but it remains unclear if brain processing of live interactive social stimuli differs substantially from processing of non-interactive social stimuli, mainly because of technical difficulties measuring brain activity during natural social interactions. This distinction is particularly important during infancy considering the importance of real-life interactions for various forms of learning. To assess the impact of live social interaction accompanied by ostensive social signals on infant cortical processing, the present study measured the cortical activities of 6-8-month-old and 10-12-month-old infants using functional near-infrared spectroscopy under contingent and non-contingent conditions (appropriately timed versus delayed responsiveness). We found greater activation over the right temporoparietal junction region in response to contingent interactions relative to non-contingent interactions in 6-8-month-old and 10-12-month-old infants. Our study indicates a critical role of contingent responsiveness for differential processing of live interactive social stimuli.