The effects of second-language age of acquisition on brain structural networks: A DTI study of high-proficient bilinguals

An increasing number of publications have focused on using the brain network perspective to study bilingual learning and cognition. However, no study analyzed the effect of second-language age of acquisition (L2 AoA) on topological properties (e.g. rich club organization) of brain white matter (WM) structural networks. In this study, we acquired diffusion tensor imaging (DTI) datasets from early and late Cantonese (L1)-Mandarin (L2) bilinguals, then constructed brain WM structural networks, and subsequently analyzed their topological properties. As compared with the late bilinguals, significantly higher global efficiency and local efficiency but lower characteristic path length were observed in the early bilinguals. In addition, the early bilinguals showed significantly higher nodal efficiency in the right rolandic operculum and gyrus rectus, as well as higher rich club coefficient and feeder connections than the late bilinguals. Taken together, these results indicated that information exchange and integration are more efficient in the early bilinguals, which provided the structural evidence for understanding the effect of L2 AoA on brain structural plasticity in bilingual learning.