ERP-based interbrain causal model reveals closed-loop information interaction in interpersonal negotiations

Uncovering the interbrain neural mechanisms underlying interpersonal negotiation offers insight into social decision-making dynamics in resource allocation. In this study, we used EEG hyperscanning alongside an iterated ultimatum game to investigate interbrain coupling and dyadic exchange behavior during negotiation. Frontal cortex event-related potentials (ERPs) revealed the distinct neural responses driven by partners' behavioral cues: the proposer's N200 differed significantly for fair versus unfair offers, and the responder's feedback-related negativity (FRN) showed a trend toward significance for the same contrast, while the proposer's N500 varied between acceptance and rejection feedback. Our analysis introduced a novel causal model based on directional phase transfer entropy (dPTE) and time-varying ERP amplitudes, illustrating directed neural processes driven by social exchange, where the proposer's brain activity initially exerts a causal impact on the responder's, whose feedback in turn influences the proposer, creating a closed-loop interaction that drives adaptive negotiation strategies. Additionally, our prediction model with autoregression with exogenous input, which incorporated these causal links between brains, demonstrated higher accuracy than single-brain or reverse causal models, underscoring the significance of dynamic interbrain coupling in interpersonal coordination. This causal model provides a mechanistic explanation of how proposer-responder pairs perceive and adapt to each other's decisions, facilitating shared attention and behavioral coordination in reciprocal, asymmetric negotiations. These findings offer a novel theoretical framework for studying complex social behaviors through interbrain dynamics and may inspire future applications in enhancing cooperative decision-making processes.