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Effects of bilingualism on brain reserve in clinical AD variants
Poster Session A, Friday, September 12, 11:00 am - 12:30 pm, Field House
Nicoletta Biondo1, Maria Luisa Mandelli1, Stephanie Grasso2, Jessica De Leon1; 1University of California, San Francisco (UCSF), 2University of Texas at Austin
Bilingualism, defined as speaking two or more languages, may contribute to cognitive reserve and serve as a protective factor against neurodegeneration. However, studies are mixed. One potential explanation for previous mixed findings is that bilingualism has network-specific effects (e.g., more protective effects on language networks compared to memory networks). For example, De Leon et al. (2020) reported a later age of symptom onset in bilingual speakers with logopenic variant primary progressive aphasia (lvPPA) compared to monolingual speakers with lvPPA. Conversely, there was no difference in age of symptom onset between monolingual and bilingual speakers with amnestic Alzheimer’s disease (AD), therefore supporting network-specific effects of bilingualism in cognitive reserve. In the current study, we aim to assess the effect of bilingualism on brain reserve. In particular, we evaluated network-specific effects of bilingualism on brain volume in monolingual and bilingual speakers with lvPPA and amnestic AD. To compare brain volume in monolingual (lvPPA: n = 67; AD: n = 119) and bilingual (lvPPA: n = 21; AD: n = 17) speakers, we preprocessed T1-weighted structural MRI data in CAT12 within SPM12 using standard procedures. From the segmented, normalized, and modulated images, we extracted cortical volumes using the Brainnetome atlas. For each participant, we then obtained ROI values of cortical volume across the entire brain. These values were harmonized by scanner, age, and total intracranial volume using ComBat tools. We employed linear mixed-effects models (LMEMs) to analyze harmonized cortical volumes in individuals with lvPPA and AD, separately. The fixed effects included bilingualism, region of interest (ROI), and their interaction. To account for subject-specific variability, random intercepts for subjects were included in the model. Sex and MMSE total scores were included as covariates. Results were FDR-corrected for multiple comparisons. Results on left-hemisphere volumes showed that bilingual lvPPA speakers had significantly larger inferior parietal lobule (IPL) volumes compared to monolingual lvPPA speakers. Conversely, among individuals with amnestic AD, no regions showed larger volumes in bilinguals compared to monolinguals. We also found larger volumes in monolingual speakers compared to bilingual speakers in certain brain regions. Monolingual lvPPA speakers had larger volumes in the middle temporal gyrus (MTG), superior temporal gyrus (STG), and medial ventral occipital cortex (MVOcC) compared to bilingual lvPPA speakers. Monolingual AD speakers, compared to bilingual AD speakers, showed significantly larger volumes across multiple memory-related and occipital regions, including the fusiform gyrus (FuG), hippocampus (Hipp), and lateral occipital cortex (LOcC). Interestingly, adding years of education—a factor that is often related to cognitive reserve—as a predictor in the LMEMs analysis significantly improved the fit of the model for the AD group, but not the model for the lvPPA group. Our findings suggest that bilingualism may contribute to network-specific cognitive and brain reserve, particularly in language-related regions. Other factors related to cognitive reserve (e.g., years of education) might affect different groups and networks in a distinct way.
Topic Areas: Multilingualism, Disorders: Acquired