Multilingualism in use and white matter changes amongst healthy middle‐aged and older adults

Abstract Background Bilingualism can stimulate brain plasticity (Jafari et al. Ann N Y Acad Sci. 2021;1505(1):8‐22) and is also associated with better executive function (Grundy. J Cult Cogn. Sci. 2020;4: 177–199). We investigated whether any feature of multilingualism (age of acquisition (AoA), proficiency or language usage) was related to change in white matter lesions and cognition amongst a cohort of middle‐aged to older adults. Method Healthy adults (N=267, age range: 45‐69, 53.56% women) from the bilingual Barcelona Brain Health Initiative cohort (BBHI, Cattaneo et al. Front Aging Neurosci. 2018 11;10) were assembled. Participants completed questionnaires of AoA for a third language (L3), level of proficiency in up to five languages and daily use of languages, up to three languages. Shannon Entropy was computed as an index measuring the proportion of languages used daily in different contexts and participants were classified as monolinguals, bilinguals or multilinguals based on this score. T1 and T2‐weighted acquisitions allowed extraction of volumes of white matter hypointensities (WMH) using Freesurfer at baseline and two years later (N=210). Stepwise regression models were conducted cross‐sectionally to investigate associations between the predicted variables (WMH and cognition) and the following predictors: age, sex, education, AoA, proficiency and Entropy levels. Linear mixed models explored changes in WMH, including fixed effects and a random intercept. Result Proficiency (high) and AoA of L3 (after puberty) were retained as factors linked to increased working memory (t=3.49, p=0.001; t=2,88, p=0.004, respectively). High proficiency was also associated with better episodic memory (EM, t=3.19, p=0.002). Multilinguals (high Entropy) presented increased WMH at baseline (t=2.39, p=0.024) and over time (F=4.41, p=0.013). Additionally, there was a slight WMH*Entropy interaction, with a steeper decline in EM amongst monolinguals, regardless of WMH changes, while multilinguals with a medium burden of WMH improved in EM (Figure 1 in green; F=2.39, p=0.065). Conclusion Multilingualism in use was linked to increased white matter change and a slightly better maintenance of EM when the burden of structural damage was low to medium. Language usage may provide the brain with an ability to cope with structural brain changes and may be considered a proxy of CR.