Microstructural plasticity in the bilingual brain

•The quantitative MRI (qMRI) technique was used to quantify and compare the microstructural properties in the bilingual brain.•Second language learning induced neuroplasticity at the microstructural level.•Early second language acquisition seems to enhance the microstructural development in language-related brain regions. The human brain has been uniquely equipped with the remarkable ability to acquire more than one language, as in bilingual individuals. Previous neuroimaging studies have indicated that learning a second language (L2) induced neuroplasticity at the macrostructural level. In this study, using the quantitative MRI (qMRI) combined with functional MRI (fMRI) techniques, we quantified the microstructural properties and tested whether second language learning modulates the microstructure in the bilingual brain. We found significant microstructural variations related to age of acquisition of second language in the left inferior frontal region and the left fusiform gyrus that are crucial for resolving lexical competition of bilinguals’ two languages. Early second language acquisition contributes to enhance cortical development at the microstructural level.