The effect of bilingualism on brain development from early childhood to young adulthood

Christos Pliatsikas,Vincent Deluca,Kyle Shattuck,Michael T Ullman,Lotte Meteyard,João Veríssimo

doi:10.1007/s00429-020-02115-5

Abstract

Bilingualism affects the structure of the brain in adults, as evidenced by experience-dependent grey and white matter changes in brain structures implicated in language learning, processing, and control. However, limited evidence exists on how bilingualism may influence brain development. We examined the developmental patterns of both grey and white matter structures in a cross-sectional study of a large sample (n = 711 for grey matter, n = 637 for white matter) of bilingual and monolingual participants, aged 3–21 years. Metrics of grey matter (thickness, volume, and surface area) and white matter (fractional anisotropy and mean diffusivity) were examined across 41 cortical and subcortical brain structures and 20 tracts, respectively. We used generalized additive modelling to analyze whether, how, and where the developmental trajectories of bilinguals and monolinguals might differ. Bilingual and monolingual participants manifested distinct developmental trajectories in both grey and white matter structures. As compared to monolinguals, bilinguals showed: (a) more grey matter (less developmental loss) starting during late childhood and adolescence, mainly in frontal and parietal regions (particularly in the inferior frontal gyrus pars opercularis, superior frontal cortex, inferior and superior parietal cortex, and precuneus); and (b) higher white matter integrity (greater developmental increase) starting during mid-late adolescence, specifically in striatal–inferior frontal fibers. The data suggest that there may be a developmental basis to the well-documented structural differences in the brain between bilingual and monolingual adults.

Highlights

Bilingualism and brain structure in adultsRecent years have seen an emerging interest in the effects that learning and using more than one language have on brain structure (Luk et al 2020)
We probed cortical thickness, surface area, and volume, while for white matter we examined both fractional anisotropy (FA) and mean diffusivity (MD)
We focus on FA and MD, since longitudinal and transversal diffusivity can be difficult to interpret (Singh et al 2018), and are often not reported or discussed in studies probing white matter integrity, including in the bilingual literature

Summary

Introduction

Bilingualism and brain structure in adultsRecent years have seen an emerging interest in the effects that learning and using more than one language have on brain structure (Luk et al 2020). Brain Structure and Function (2020) 225:2131–2152 in white matter tracts that connect these regions (for recent reviews, see Hayakawa and Marian 2019; Pliatsikas 2019) These findings suggest that bilingualism/multilingualism (referred from here onwards as bilingualism) is on par with other types of longer term experience that lead to significant structural brain changes during the acquisition and maintenance of a new skill, such as juggling, the use of novel tools, and navigation (Maguire et al 2000; Draganski et al 2004; Quallo et al 2009; Taubert et al 2010). Bilingualism may be expected to affect the structure of cortical and subcortical regions involved in (perhaps among other functions) language learning, processing, and control, as well as the white matter tracts that provide connectivity between these regions.

Methods

Results

Conclusion