Superior Frontal Gyrus Cortical Thickness Mediates the Association Between Openness to Experience and Theory of Mind: Evidence from the Human Connectome Project

Background: Theory of mind (ToM), the capacity to infer the mental states of others, varies considerably across healthy adults. Openness to experience has been linked both to social-cognitive abilities and to thinner prefrontal cortex, but whether cortical structure statistically accounts for the association between openness and ToM is unknown. We tested whether bilateral superior frontal gyrus (SFG) cortical thickness mediates this association. Methods: Data from 1,049 healthy young adults with complete data were drawn from the Human Connectome Project. ToM was indexed by accuracy on the Heider-Simmel social animation task, openness by the NEO Five-Factor Inventory, and SFG thickness by FreeSurfer. Models adjusted for age, sex, intracranial volume and fluid intelligence; indirect effects were tested with 5,000 bootstrap resamples, and Benjamini-Hochberg false discovery rate correction was applied. Results: Openness showed a positive total effect on ToM accuracy (beta = .081, p = .009). Higher openness was associated with thinner left and right SFG (beta = -.085 and -.084), and thinner SFG with higher ToM accuracy (beta = -.082 and -.075). Indirect effects were significant (left: .0069, 95% CI [.0010, .0158]; right: .0063, 95% CI [.0007, .0146]), accounting for approximately 8.5% and 7.8% of the total effect, and remained significant after rank-based normalisation of the ceiling-affected ToM scores. Conclusions: SFG cortical thickness partially and statistically mediates the association between openness to experience and social cognition. Because the data are cross-sectional and effects are small, the findings do not establish a causal mechanism, neural efficiency or synaptic pruning, but they identify a candidate structural pathway for longitudinal testing.