The neural-physiological coupling mechanism underlying positive emotion sharing boosting interpersonal connection among strangers

Emotional sharing plays a crucial role in boosting interpersonal connections among strangers. The present study aims to explore the emotion regulation and social connectedness function of emotional sharing among strangers and the underlying neural-physiological coupling mechanism during dyadic face-to-face interactions. Thirty-five stranger dyads (sharer vs. listener) completed the emotion sharing task (positive, neutral and negative) in which sharers recalled emotional events then shared their emotions to the listener. We recorded each pair of participants’ brain activities (using functional near-infrared spectroscopy), physiological signals (heart rate) and self-rated emotional states simultaneously. Our results revealed that both the sharer and the listener’s positive affect were significantly increased through positive emotion sharing, and listeners rated sharers as more interpersonally attractive after positive emotion sharing compared to neutral or negative sharing. At the neural level, interpersonal brain synchronization (IBS) between the sharer’s right primary somatosensory cortex (rPSC) and the listener’s left fusiform gyrus (lFG) was significantly higher in both positive and neutral conditions than in the negative condition. During positive sharing, rPSC sharer –lFG listener IBS was positively associated with the listener’s closeness increment, IPS was positively associated with listeners’ valence increment, and higher IBS patterns predicted sharers’ greater interpersonal trust increment when IPS pattern was higher. Together, these neural and physiological synchrony measures jointly predicted the sharer’s perceived interpersonal trust towards the listener. In sum, our converging multimodal behavioral, physiological, and neural evidence revealed that positive emotion sharing played a central role in enhancing neural-physiological coupling and fostering interpersonal connections between stranger dyads. Significance statement : Sharing positive experiences is among the most common and consequential acts in social life, yet the neurophysiological mechanisms by which it forges bonds between strangers are unknown. Using simultaneous fNIRS brain imaging and heart rate recording during dyadic interactions, our work reveals that the sharing of positive emotions has a distinct function beyond strengthening synchrony: it makes neural and physiological coupling socially meaningful. Specifically, during positive sharing, this synchrony is linked to the listener’s emotional resonance and intimacy with the sharer, and to the sharer’s trust in the listener. These findings provide the first multimodal neurophysiological account of how shared positive affect rapidly transforms strangers into socially connected partners.