Slide Slam L5
Bilingual experience affects white matter integrity across the lifespan
Toms Voits1, Vincent DeLuca1; 1UiT the Arctic University of Norway
Bilingual experience has been reported to change the structure and function of the brain across the lifespan (Bialystok, 2021). In the latter stages of life bilingualism has also been associated with increases in compensatory mechanisms to age-related neurocognitive decline thus delaying dementia symptom onset and leading to a more favorable trajectory of neurocognitive aging more generally (Perani & Abutalebi, 2015). However, most research to date has examined bilingualism-induced effects on neurocognition within one of the above age groups – with middle-aged individuals typically not being a population of interest – meaning there is little evidence for how bilingual experience affects the trajectory of neural decline across the lifespan. Furthermore, bilingualism is often treated as a dichotomous variable, despite it being quite a heterogeneous experience on an individual level (Leivada et al., 2020; Luk & Bialystok, 2013). Therefore, our knowledge of how degree of bilingual engagement modulates neural outcomes across all age groups is insufficient. In the present study we employed diffusion tensor imaging (DTI) to examine whether bilingualism and the degree of engagement in bilingual language use modulates the nature or rate of white matter decline associated with aging. DTI data and language history data, via the language and social background questionnaire (LSBQ; Anderson et al., 2018), were collected from a cohort of monolingual and bilingual individuals (n=78) spanning a wide age range (30-84 yrs.). We investigated mean diffusivity (MD) and fractional anisotropy (FA) values, both in whole-brain as a measure of total brain health, and in several white matter tracts, which are implicated in bilingual language control and aging, including the corpus callosum (CC), bilateral inferior fronto-occipital fasciculi (IFOF), and bilateral superior longitudinal fasciculi (SLF) (Anderson et al., 2018; Gold et al., 2012; Hämäläinen et al., 2017; Luk et al., 2011). Two separate analyses were run. First, generalized additive models were run on a matched monolingual and bilingual sample, examining effects of age on the trajectory of white matter integrity and how bilingualism modulates this effect. This analysis revealed a significant effect of age within the monolingual group for whole brain MD, right IFOF MD, and right SLF FA. However, the age effect within the bilingual group was not significant, indicating a more rapid decline in white matter integrity more rapidly within the monolingual cohort. Second, general linear models were run on the entire participant sample, which examined an interaction between age and degree of bilingual engagement (via continuous measures of bilingualism derived from the LSBQ) on white matter integrity. This analysis revealed a significant interaction of age and degree of bilingual engagement on white matter integrity measures in several regions of interest. Notably, bilingual engagement was found to affect whole brain MD and FA values, indicating that lesser engagement in bilingual language use across the lifespan correlates with a steeper decline in white matter integrity with age. Together these results indicate bilingualism, and, specifically, degree of bilingual engagement, is a significant factor that impacts the trajectory of age-related decline in white matter integrity across the lifespan.