Inter-brain Synchronization Is Weakened by the Power to Reject Offers in Bilateral Bargaining Games

Bargaining is an essential part of our lives; however, there has been little research focusing on inter-brain neural mechanisms underlying bilateral bargaining. In the current study, we employed the electroencephalography (EEG) hyperscanning technique to investigate how the power to reject offers influences neuronal correlation between bargainers. As the bilateral bargaining game can be converted into either the ultimatum game or the dictator game according to whether the responder does or does not have the power to reject offers during the bargaining process, it provides a proper framework for investigating this topic. When responders were able to reject offers, proposers provided fair offers more often, providing behavioral evidence for the effect of the power to reject offers on bargaining. Combining previous neuroimaging evidence, our event-related potential results showed a significant medial frontal negativity (MFN) in the dictator game when the responder faced a disadvantageous inequitable offer. The results revealed the effect of the power to reject offers on the psychological activity of responders and the corresponding neural mechanisms, suggesting that this power elicited an angry response in the responder to an unfair offer, rather than a cognitive response (i.e., a concern for fairness). Most importantly, the current study found a significantly greater inter-brain synchronization in high-frequency bands (beta, 13–30 Hz; gamma, 31–50 Hz) in the dictator game than in the ultimatum game. A shared norm concern hypothesis was proposed to identify a possible mechanism. The results suggest that when both bargainers attach great importance to social norms (e.g., fairness or cooperation) in their decision-making or judging process, their neural activities become more synchronized. This study provides evidence for the role of the power to reject offers on inter-brain synchronization during the bargaining process, and proposes a potential mechanism for inter-brain synchronization in decision-making tasks.