The medial prefrontal cortex contributes to representing shared goals among group Members: Evidence from tDCS

People often generalize the actions of known group members to unfamiliar members based on their goals. This goal-based action generalization is constrained by the belief that group members have a shared goal, which typically results in a nongraded pattern where the extent of generalization does not gradually increase with the prevalence of action goals. In the present study, 90 healthy participants (aged 15–27) were randomly assigned to three equal groups, each receiving one of three types of transcranial direct current stimulation (tDCS) targeting the medial prefrontal cortex (mPFC): anodal (anodal electrode over Fpz, return electrode over Oz), cathodal (reverse montage), or sham stimulation. In the implicit task, cathodal stimulation—diminishing mPFC excitability—weakened the representation of the shared-goal belief, leading to a graded generalization pattern in which expectations increased with action prevalence. In contrast, both anodal and sham stimulation produced the typical nongraded pattern. In the explicit task, both anodal and cathodal stimulation produced the similar graded generalization, while sham stimulation preserved the nongraded pattern. These findings suggest that the medial prefrontal cortex (mPFC) is involved in representing the belief that group members have a shared goal. This study advances our understanding of how the mPFC contributes to social cognition by integrating beliefs with statistical evidence to guide action expectations.