EEG hyperscanning reveals dynamic interbrain network patterns during interactive social decision-making

Social decision-making involves intricate and dynamic interactions between brains, yet prior hyperscanning research primarily concentrated on investigating the overall patterns of interbrain synchrony (IBS), leaving its fine-grained temporal dynamics unveiled. Here, after recording the electroencephalography of proposer-responder pairs who engaged in an iterated ultimatum game, time-varying IBS network architectures were explored by leveraging source-localized wavelet transform coherence and k-means clustering. Results revealed a sequence of temporally and functionally distinct IBS states along the response and feedback periods. Early states, occurring around stimulus onset, were dominated by a posterior parietal modular configuration, likely associated with shared attention and visual processing. In contrast, later states during the decision-feedback stage involved increased IBS in the frontal and temporoparietal regions, reflecting coordinated activity between interacting partners supporting decision execution and adaptive behavioral adjustments. Crucially, advantageous conditions (fair proposal or acceptance feedback) elicited more active and efficient dynamic IBS states than disadvantageous conditions (unfair proposal or rejection feedback), with greater IBS related to increased reciprocal behavior. These findings reveal recurring IBS patterns, suggesting that social decision-making is modulated not only by temporal fluctuations in IBS networks but also by flexible interbrain communication between key cortical regions.