Forget and Forgive: A Neurocognitive Mechanism for Increased Cooperation During Group Formation

Abstract

How do group size changes influence cooperation within groups? To examine this question, we performed a dynamic, network-based prisoners dilemma experiment with fMRI. Across 83 human subjects, we observed increased cooperation as group size increased. However, our computational modeling analysis of behavior and fMRI revealed that group size itself did not increase cooperation. Rather, interaction between (1) subjects stable prosocial tendencies, and (2) dynamic reciprocal strategy weighted by memory confidence, underlies the group size-modulated increase in cooperation because the balance between them shifts toward the prosocial tendency with higher memory demands in the larger groups. We found that memory confidence was encoded in fusiform gyrus and precuneus, whereas its integration with prosocial tendencies was reflected in the left DLPFC and dACC. Therefore, interaction between recall uncertainty during reciprocal interaction (i.e., forgetting) and ones individual prosocial preference is a core pillar of emergent cooperation in more naturalistic and dynamic group formation.