A BIO-EEG Hyperscanning Study of Moral Dyadic Negotiation

Background/Objectives: Recent social neuroscience research has increasingly shifted from individual moral decision-making to the study of how people negotiate moral dilemmas in interpersonal contexts. This multimethod hyperscanning study investigated whether initial differences in moral decision-making orientation within a dyad influence neural and autonomic synchronization during a joint moral negotiation. Methods: Fourteen dyads were classified as homologous or heterologous based on the similarity or dissimilarity of their individual decision-making orientations. Each dyad was asked to negotiate and reach a shared decision on a moral dilemma involving a realistic health emergency scenario. Electroencephalography (EEG) and autonomic signals were recorded simultaneously. Dissimilarity indices were computed to assess inter-brain and autonomic synchronization. Results: EEG analyses revealed a significant effect only in the delta frequency band: all dyads, regardless of orientation, showed greater dissimilarity in the left frontal region compared to the left temporo-central and right parieto-occipital regions. In addition, autonomic data indicated greater heart rate variability (HRV) dissimilarity in homologous dyads than in heterologous ones. However, these results did not confirm our initial hypotheses, indicating the opposite pattern. Conclusions: Left frontal delta dissimilarity emerged as an exploratory candidate marker of moral negotiation across dyads. Greater HRV dissimilarity in homologous dyads suggests that, in these dyads, successful negotiation may be supported by complementary rather than synchronized autonomic responses. This multimethod hyperscanning approach highlights the complex and partially dissociable contributions of neural and autonomic processes to the regulation of shared moral decision-making.