Sequential language learning versus language immersion in bilingualism: Diffusion MRI connectometry reveals microstructural evidence

Abstract

Background: Bilingualism is a universal phenomenon. Study of bilingual brain has provided evidence to probable advantageous outcomes of early second language learning and brain structural correlates to these outcomes. Preservation of cognitive function with aging and executive dexterity are amongst proposed benefits. Method: Using the data deposited by Pliatsikas we analyzed through diffusion MRI connectometry structural difference in white matter tracts in 20 healthy sequential bilingual adults, who used English as a second language on a daily basis, and 25 controls in fiber differentiation analyses. Significant tracts were extracted with and without regression against language immersion period. Results: Connectometry results revealed increased connectivity in corpus callosum (CC), bilateral cingulum, arcuate fasciculus (AF), and left Inferior fronto occipital fasciculus (IFOF), of sequential bilingual adults. Also bilateral IFOF, AF as well as body and genu of corpus callosum were positively correlated with language immersion time. Conclusion: Mentioned white matter tracts with diffusion structural significance in young adults with long immersion into the second language, confirm results of previous results. These are also in consort with known pathways involved in neurophysiological processes in speech stream and in cognitive performance. Insertion of immersion time as a variable in the model, yielded the same results with higher FDR values, except for arcuate fasciculus. Future studies are warranted to address structural differences with larger samples, investigating the effects of early language immersion on white matter tracts versus individual and social variables that interfere with white matter maturation and integrity.