Interpersonal coordination enhances brain-to-brain synchronization and influences responsibility attribution and reward allocation in social cooperation

Fair distribution of resources matters to both individual interests and group harmony during social cooperation. Different allocation rules, including equity- and equality-based rules, have been widely discussed in reward allocation research; however, it remains unclear whether and how individuals' cooperative manner, such as interpersonal coordination, influence their subsequent responsibility attribution and reward allocation. Here, 46 dyads conducted a time estimation task-either synergistically (the coordination group) or solely (the control group)-while their brain activities were measured using a functional near-infrared spectroscopy hyperscanning approach. Dyads in the coordination group showed higher behavioral synchrony and higher interpersonal brain synchronization (IBS) in the dorsal lateral prefrontal cortex (DLPFC) during the time estimation task than those in the control group. They also showed a more egalitarian tendency of responsibility attribution for the task outcome. More importantly, dyads in the coordination group who had higher IBS in the dorsal medial prefrontal cortex (DMPFC) were more inclined to make egalitarian reward allocations, and this effect was mediated by responsibility attribution. Our findings elucidate the influence of interpersonal coordination on reward allocation and the critical role of the prefrontal cortex in these processes.