Forget and Forgive: Memory Constraints Enhance Cooperation in Dynamic Groups

Abstract

Understanding how group size influences cooperative behavior is crucial in economics and behavioral sciences. We investigated this phenomenon using a dynamic network-based Prisoner's Dilemma game combined with fMRI imaging. Contrary to traditional predictions, we observed that cooperation among participants increased as group size expanded. Computational modeling revealed that this effect was not a direct result of group size. Instead, it emerged from the interaction between individuals' stable prosocial tendencies and a reciprocal strategy modulated by memory confidence. In larger groups, the cognitive load impairs memory of past interactions, leading individuals to rely more on their inherent prosocial preferences rather than reciprocity. Neuroimaging data showed that memory confidence was encoded in the fusiform gyrus and precuneus, while its integration with prosocial tendencies involved the dorsolateral prefrontal cortex and dorsal anterior cingulate cortex. These findings suggest that memory limitations during reciprocal interactions shift behavior toward prosociality, providing a neurocognitive mechanism by which larger groups may foster increased cooperation despite traditional economic expectations.