Redefining bilingualism as a spectrum of experiences that differentially affects brain structure and function

TLDR

Learning and using a second language affects brain structure and function, yet evidence varies because bilingualism has been treated categorically rather than as a dynamic experience. The study investigates how experience‑based factors in bilingual language use influence brain structure and functional connectivity. Experience‑based factors comprise measures of everyday second‑language use across immersive settings, such as social usage. Analyses show that brain structure and functional connectivity adapt to individual experience‑based factors, enabling maximally efficient processing and control of two languages.

Abstract

Learning and using an additional language is shown to have an impact on the structure and function of the brain, including in regions involved in cognitive control and the connections between them. However, the available evidence remains variable in terms of the localization, extent, and trajectory of these effects. Variability likely stems from the fact that bilingualism has been routinely operationalized as a categorical variable (bilingual/monolingual), whereas it is a complex and dynamic experience with a number of potentially deterministic factors affecting neural plasticity. Here we present a study investigating the combined effects of experience-based factors (EBFs) in bilingual language use on brain structure and functional connectivity. EBFs include an array of measures of everyday usage of a second language in different types of immersive settings (e.g., amount of use in social settings). Analyses reveal specific adaptations in the brain, both structural and functional, correlated to individual EBFs and their combined effects. Taken together, the data show that the brain adapts to be maximally efficient in the processing and control of two languages, although modulated ultimately by individual language experience.