The anatomical basis of morpho-syntactic computation reflected in gray matter volume and pattern of the inferior frontal gyrus.

This study examined whether gray matter (GM) volume in the inferior frontal gyrus (IFG)-specifically the pars triangularis and pars orbitalis-could predict individual sensitivity to morpho-syntactic violations. Native speakers of Korean performed a lexical decision task involving transposed syllable stimuli that either preserved or violated morphological boundaries. Behavioral efficiency was measured using inverse efficiency scores (IES), and structural brain data were analyzed via voxel-based morphometry. Univariate partial correlation analysis showed a significant negative association between GM volume in the left pars triangularis and IES difference scores (across-boundary minus replaced-control), suggesting that individuals with greater volume in this region are more sensitive to morpho-syntactic structure. No such effect was observed for the pars orbitalis. Multivariate pattern analysis (MVPA) further revealed that distributed GM patterns in both IFG subregions significantly predicted morpho-syntactic sensitivity. These findings remained robust under permutation testing that controlled for demographic and anatomical covariates. While the present study examined morpho-syntactic processing in participants' native language, the findings offer insight into inter-individual variability in IFG morphology, which may support language-specific computations.