Lifelong Bilingualism Maintains White Matter Integrity in Older Adults

Luk, Gigi; Bialystok, Ellen; Craik, Fergus I. M.; Grady, Cheryl L. · 2011 · OpenAlex-citations

DOI: 10.1523/jneurosci.4563-11.2011

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Summary

This study investigates the neural mechanisms underlying the cognitive advantages observed in older bilingual adults, specifically testing whether lifelong bilingualism preserves white matter (WM) integrity against age-related decline. Previous research established that bilinguals exhibit superior executive function compared to monolinguals, but the structural basis for this behavioral difference remained unclear. The authors hypothesized that the constant cognitive control required to manage two languages enhances WM connectivity, thereby providing a neural basis for "brain reserve." The researchers conducted a comparative analysis of 28 healthy older adults (mean age 70.5 years), divided equally into monolingual and lifelong bilingual groups. Participants underwent neuropsychological testing to ensure comparable cognitive performance and demographic backgrounds, followed by magnetic resonance imaging. The study utilized diffusion tensor imaging (DTI) to measure WM integrity via fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD). Additionally, resting-state functional MRI was employed to assess functional connectivity in frontal lobe regions adjacent to WM areas showing group differences. Data were analyzed using Tract-Based Spatial Statistics and seed-based partial least squares analysis. The results demonstrated that lifelong bilinguals maintained higher WM integrity than monolinguals. Specifically, bilinguals exhibited significantly higher FA values in the corpus callosum, extending to the bilateral superior longitudinal fasciculi and the right inferior frontal–occipital fasciculus. This preservation of integrity was driven by lower radial diffusivity in bilinguals, indicating reduced water diffusion perpendicular to axons, while no differences were found in axial diffusivity. Functionally, bilinguals displayed stronger anterior-to-posterior functional connectivity, linking frontal regions with temporal, parietal, and occipital areas. In contrast, monolinguals showed stronger functional connectivity restricted to anterior frontal regions. These structural and functional patterns were observed despite equivalent behavioral performance between groups. The findings provide the first evidence that naturally occurring lifelong experience, such as bilingualism, is associated with maintained WM integrity in older adults. The enhanced structural connectivity and more distributed functional networks in bilinguals suggest a mechanism for brain reserve, potentially compensating for age-related neural deterioration. This study implies that the cognitive demands of managing two languages may protect against WM decline, offering a structural explanation for the bilingual advantage in executive function and highlighting the role of enriched life experiences in healthy brain aging.

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• cognitive impairment