Abstract
Interbrain synchrony (IBS) is thought to reflect the flow of information between individuals and interpersonal mechanisms like empathy and bonding. Previous research suggests that IBS varies according to different factors, including interpersonal bond type, individual characteristics, emotional valence and physical presence/absence. This study investigated how IBS in mother-child dyads varies during imagined emotional situations, focusing on valence and imagined presence/absence of the mother. We used functional near-infrared spectroscopy (fNIRS) hyperscanning to measure IBS over the right prefrontal cortex, dorsolateral prefrontal cortex and temporoparietal junction in 38 mother-child dyads (child age: 10–14 years). Results showed that IBS differed across valence only when participants imagined the mother being present, with higher IBS in negative situations than in positive ones. Furthermore, in scenarios imagined with the mother present, IBS was associated with the mother’s personal distress —negative correlation in positive scenarios, and positive correlation in negative scenarios—and with children’s secure base support scores—negative association in the frontopolar cortex. These findings suggest that mothers and children perceive being together differently, depending on emotional valence, social context and individual differences. Overall, our results suggest that IBS reflects dyadic emotional processing and highlight associations with individual traits in dyadic neural synchrony. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1038/s41598-026-43086-7.