This meta-analysis synthesized functional magnetic resonance imaging (fMRI) studies examining neural activation patterns during group categorization tasks in healthy adults. The analysis included 66 studies (108 contrasts, 518 foci) for in-group > out-group processing and 35 studies (61 contrasts, 371 foci) for out-group > in-group processing. Specific analyses focused on ethnicity-based categorization (38 studies, 59 contrasts, 279 foci) and empathy processing tasks (30 studies, 50 contrasts, 260 foci).
For in-group > out-group processing, researchers identified 22 significant activation likelihood estimation (ALE) clusters. Conversely, out-group > in-group processing showed 25 significant clusters. In ethnicity-based categorization tasks, 27 significant clusters indicated in-group bias, while empathy processing tasks revealed 23 significant clusters for in-group bias. Effect sizes and p-values/confidence intervals were not reported for these findings.
Safety and tolerability data were not reported in this neuroimaging meta-analysis. A key limitation noted by the authors is that previous meta-analyses treated all group memberships and task types as homogenous entities, potentially overlooking systematic variations in neural activation patterns.
The practice relevance suggests that interventions targeting group processing biases may need to address specific group-task combinations rather than assuming universal neural mechanisms. The findings indicate multiple neural pathways may underlie different aspects of group processing, with ethnicity-based categorization and empathy processing showing distinct activation patterns.
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INTRODUCTION: Systematic variations in neural activation patterns during processing of group categorization is a facet often overlooked in extant meta-analyses that typically treated all group memberships and task types as homogenous entities. Recognizing the necessity to differentiate between various group memberships and task types due to them eliciting distinct neural activity, our study addressed this gap by conducting a more fine-grained exploration.
METHODS: A comprehensive meta-analytic approach using the activation likelihood estimation (ALE) following PRISMA guidelines was employed. Inclusion criteria were task-fMRI studies, whole-brain analyses in a standard stereotaxic space, involved healthy adults, and published in English. Meta-analyses were performed using GingerALE.
RESULTS: Overall in-group > out-group (IG>OG) processing included 66 studies (108 contrasts, 518 foci), and ALE analysis revealed 22 significant clusters, with the largest (3328 mm) located in the left insula, inferior frontal gyrus, and uncus. Overall OG > IG processing included 35 studies (61 contrasts, 371 foci), and ALE analysis revealed 25 significant clusters, with the largest (1728 mm) located in the right presupplementary motor area. Group membership classification found 38 ethnicity studies on in-group bias (IG>OG; 59 contrasts, 279 foci), and ALE analysis revealed 27 significant clusters, with the largest (1616 mm) located in the right superior occipital gyrus, right middle occipital gyrus, right middle temporal gyrus, and right fusiform gyrus. fMRI task types found 30 studies in empathy processing on in-group bias (IG>OG; 50 contrasts, 260 foci), and ALE analysis revealed 23 significant clusters, with the largest (2480 mm) located in the right postcentral gyrus, and right posterior cingulate gyrus.
CONCLUSION: Our unrestricted search approach with ALE methodology extends beyond previous categorically constrained meta-analyses by capturing group dynamics not limited to predefined categories. The distinct activation patterns for ethnicity-based categorization and empathy processing tasks indicate multiple neural pathways rather than universal mechanisms for group processing. These context-dependent patterns suggest interventions must target specific group-task combinations rather than assume uniform neural processes.
