Multilingualism as a factor of resilience to Alzheimer's disease and related dementias in India

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Project Summary/Abstract By 2050, two-thirds of older individuals with dementia will live in low-and middle-income countries (LMICs). As LMICs continue to experience a reduction in mortality, it is critical to determine factors that confer protection and resilience toward Alzheimer’s disease and related dementias (ADRD). Some studies find that bilinguals are at reduced ADRD risk compared to monolinguals, but other studies do not find evidence of a bilingual advantage. The rationale for this study is that the equivocal findings of prior research has been driven largely by methodological inconsistencies that limit our understanding of bilingualism’s role in cognitive aging such as: 1) inadequate control for potential confounders that limit our ability to infer whether bilingualism has a direct effect on cognition or whether these relationships are due to environmental and sociocultural factors, 2) limited inclusion of markers of neuropathology, and 3) little attention given to within-group differences among bilinguals, such as age of second language (L2) acquisition, proficiency, frequency of language use, number of languages spoken, and diversity of language families. India offers a unique opportunity to study the role of bilingualism in cognitive reserve and resilience, given its rich linguistic and sociocultural diversity across the country. The overall aim of the study is to leverage the unique features of India’s linguistic and sociodemographic landscape to discern whether bilingualism modifies the association between blood-based and neuroimaging biomarkers of ADRD and cognition and cognitive decline. This study will analyze available plasma-based measures of amyloid and tau pathologies, MRI, and cognitive assessments from the Longitudinal Aging Study in India–Diagnostic Assessment of Dementia (LASI-DAD), a large, population-representative study of ageing and dementia in India. Specifically, the project will 1) determine whether bilingualism modifies the association between ADRD biomarkers (blood-based or neuroimaging) and cognitive outcomes, 2) evaluate whether the protective effect of bilingualism differs across diverse life-course environmental determinants of health, and 3) deconstruct language use within bilinguals in India to understand the mechanisms by which bilingualism confers cognitive reserve against biological risk of ADRD. We hypothesize that bilingualism will buffer the effects of blood AD-biomarkers (amyloid, and tau plasma levels), cortical atrophy, and white matter integrity on baseline cognition and rate of cognitive decline compared to monolinguals in the domains of memory, language, and executive functioning. In addition, by deconstructing bilingualism, we hypothesize that earlier age of L2 acquisition, higher bilingual proficiency, greater daily multiple language use, higher number of languages acquired, and greater distance between language families will confer cognitive reserve, independent of confounding sociocultural factors (i.e., education, socioeconomic status). This proposal will enhance the field of ADRD by uncovering the underlying mechanisms of resilience to ADRD that may be modifiable and transferable to other populations.