Relationship-context differences in inter-brain synchrony during cooperative coordination and shared emotional viewing: An fNIRS hyperscanning study.

Interpersonal neural coordination may vary across close-relationship contexts, yet direct comparisons between friendship and romantic relationships remain limited. This study used functional near-infrared spectroscopy (fNIRS) hyperscanning to compare inter-brain synchrony (IBS) between female-female friend dyads and heterosexual romantic dyads during cooperative coordination and shared emotional video viewing. Thirty dyads were initially recruited, and 13 dyads in each group were included in the final analyses. During the cooperative coordination task, female-female friend dyads showed greater IBS than heterosexual romantic dyads in the right inferior frontal gyrus (IFG). No significant main effect of block or dyad type × block interaction was observed. During the shared emotional video-viewing task, heterosexual romantic dyads showed greater IBS than female-female friend dyads in the middle frontal pole and right IFG. No significant between-group differences were observed in the corresponding behavioral measures, and IBS was not significantly associated with behavioral performance. These findings suggest that interpersonal neural coordination varies across close-relationship contexts and task settings. Rather than indicating categorical differences in cognitive or affective empathy, the observed IBS patterns may reflect context-dependent differences in the neural processes supporting cooperative coordination and shared emotional experiences. These findings should be interpreted cautiously given the modest sample size and the confounding of relationship type with dyadic sex composition.