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

Emotional sharing plays a crucial role in boosting interpersonal connections among strangers. The present study aims to explore the interpersonal emotion regulation and social connectedness function of emotional sharing among strangers and the underlying neural-physiological coupling mechanism. 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 sharers and listeners' 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 listeners' closeness increment, interpersonal physiological synchrony (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 the most common and consequential act in social life, yet the neurophysiological mechanisms by which it forges bonds between strangers remain unknown. Using simultaneous fNIRS brain imaging and heart rate recording during dyadic interactions, we reveal 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.