The Relevance of Dual Language Experience in Interhemispheric Brain Connectivity in Older Adults

Abstract Objectives to analyze the volumes of sections of the corpus callosum (CC) and the integrity of the interhemispheric fibers that connect homotopic regions of the frontal and temporal lobes in bilinguals and monolinguals and to correlate neuroimaging data with cognitive measures and bilingual variables. Method 107 bilinguals and 89 monolinguals from the 1Florida ADRC were clinically diagnosed as cognitively normal (CN), MCI, or dementia; mean age = 71.28 (10.94). CC volume was calculated from a T1-weighted scan using Freesurfer. Free water (FW) and free water-corrected fractional anisotropy (FAt) maps were calculated from a diffusion MRI scan within frontal and temporal transcallosal tracts (TCATT). Results Bilinguals had a larger proportion of the anterior CC volume compared to monolinguals independent of the diagnostic group. FAt values in the Supplementary Motor Area (SMA) and the inferior temporal lobe tracts (IT TCATTs) were higher in bilinguals compared to monolinguals indicating better white matter integrity. A significant interaction demonstrated that these values were higher in bilinguals for the dementia group. Correlations were significant between the SMA FW values and several cognitive tests particularly executive function tests in both language groups. In bilinguals, the IT TCATTs correlated with language test scores. FAt in the SMA TCATT correlated with the percentage of English exposure and FAt in the IT TCATTs positively correlated with English proficiency. Conclusions Bilingualism interacts with cognitive status in aging and is associated with CC volume and the integrity of white matter in the frontal and temporal lobes supporting its role in the increase of neural reserve.