Diffusion tensor imaging was used to compare white matter structure between American monolingual and Spanish-English bilingual adults living in the United States. In the bilingual group, relationships between white matter structure and naturalistic immersive experience in listening to and speaking English were additionally explored. White matter structural differences between groups were found to be bilateral and widespread. In the bilingual group, experience in listening to English was more robustly correlated with decreases in radial and mean diffusivity in anterior white matter regions of the left hemisphere, whereas experience in speaking English was more robustly correlated with increases in fractional anisotropy in more posterior left hemisphere white matter regions. The findings suggest that (a) foreign language immersion induces neuroplasticity in the adult brain, (b) the degree of alteration is proportional to language experience, and (c) the modes of immersive language experience have more robust effects on different brain regions and on different structural features.Graphical abstract
White matter regions most affected by immersive second language experience.