Group Identity Enhances Inter-brain Synchronization in the Hold-Up Problem

The hold-up problem is common and often has profound implications, often related to the exclusivity of assets in incomplete contracts. Research has shown that group identity can resolve or alleviate the hold-up problem. However, it remains an open question how group identity affects inter-brain synchronization in the hold-up problem. In the present study, we implemented a hold-up game while recording their brain activity by EEG-based hyperscanning techniques. We used two treatments to explore the potential effects of group identity created by categorization only (NoChat treatment) and group identity created by categorization and chat-enhanced (Chat treatment) on subjects' inter-brain synchronization during the hold-up game. Brain imaging results showed in the Alpha-band, group membership (ingroup vs outgroup) and Online chat (NoChat vs Chat) had a remarkable impact on inter-brain synchronization, and significant ROIs were mainly concentrated in frontal and temporal regions, Moreover, ingroup members had significantly higher inter-brain synchronization than outgroup members in the significant ROIs, and this enhanced inter-brain synchronization was notably connected to an upsurge in dyads' group identity. inter-brain synchronization was lower in the NoChat treatment than Chat treatment in the significant ROIs. These discoveries also give evidence for the impact of group identity on inter-brain synchronization in the hold-up problem and reveal inter-brain mechanisms of social interaction.