White-matter microstructure differs in adult bilingual and monolingual brains

Behavioral research indicates that bilingual children and adults outperform monolinguals at executive function tasks, especially those related to cognitive flexibility, suggesting that experience with two languages alters brain structure. We investigated white-matter microstructure using Tract-Based Spatial Statistics (TBSS) in monolingual (n = 15) and Spanish-English bilingual (n = 16) adults, quantifying fiber tract organization in measures of directionality (fractional anisotropy, FA) and diffusivity perpendicular to the main axonal direction (radial diffusivity, RD). FA was significantly higher for monolinguals (p < 0.05, corrected) in three brain regions: the right posterior limb of the internal capsule, the right sagittal stratum that includes inferior frontal occipital fasciculus, and the right thalamus. RD was greater for bilinguals (p < 0.05, corrected) in multiple brain areas, most prominently in the cerebellum, inferior frontal occipital fasciculus, and superior longitudinal fasciculus. We inte...