A Meta-Analysis of Functional Magnetic Resonance Imaging Studies on In-Group and Out-Group Categorization

Abstract

This meta-analysis examined systematic variation in neural activation during in-group and out-group categorization. Using activation likelihood estimation and PRISMA-guided methods, the study analyzed task-fMRI studies of healthy adults that reported whole-brain results in standard stereotaxic space. Overall in-group greater than out-group processing showed significant clusters including the left insula, inferior frontal gyrus, and uncus, while out-group greater than in-group processing showed clusters including the right presupplementary motor area. Analyses by group membership and task type revealed distinct patterns for ethnicity-based categorization and empathy processing. The findings suggest that group processing is not governed by a single universal neural mechanism, but varies by social category and task context.