Inter-brain synchrony during collaborative gaming: an investigation using theta-burst stimulation at the right temporal-parietal junction

Although hyperscanning experiments have revealed robust inter-brain synchrony (IBS) during social interaction, the specific neural mechanisms through which IBS contributes to collaborative performance remain unclear. While prior studies have provided preliminary causal evidence linking IBS to collaboration, it is unknown whether IBS within specific social-cognitive regions, such as the right temporoparietal junction (rTPJ), plays a causal role. To address this, the current study employed theta-burst stimulation (TBS) to modulate cortical activity in the rTPJ-a key region of the mentalizing network-before participant pairs played 7-minute Tetris games together and individually. Thirty-three same-gender stranger dyads participated in a total of three sessions: no TBS, continuous TBS, and intermittent TBS. Functional near-infrared spectroscopy (fNIRS) was used to measure IBS at the prefrontal cortex (PFC) and rTPJ during collaborative versus individual Tetris. IBS was stronger during collaborative compared to individual Tetris, with IBS at the PFC greater than at the rTPJ. However, modulating rTPJ activity did not causally alter the relationship between IBS and collaborative Tetris performance. Intriguingly, a negative relationship between collaborative Tetris performance and IBS was found. Questionnaire data revealed that participants rated their partners as more likeable after collaborating regardless of their collaborative performance or TBS condition. Together, these findings suggest that while IBS reliably emerges during collaboration, its causal role-particularly at the rTPJ-may be more nuanced than previously assumed, calling for deeper investigation into the functional significance of IBS in social interaction.