Multilingualism and cognitive reserve in older adults with, or at risk for, Alzheimer's disease: Evidence from resting-state functional connectivity.

Speaking more than one language is hypothesized to lead to greater brain resilience in aging and Alzheimer's disease, resulting in a delay in the symptom onset of Alzheimer's disease. While previous research has used structural neuroimaging measures to explore the neural underpinnings of this protective effect, few studies have used functional brain measures. Thus, we used functional connectivity measures of resting-state fMRI data to explore the association between multilingualism and brain resilience in older adults with, or at risk for, Alzheimer's disease. Participants were selected from The Comprehensive Assessment of Neurodegeneration and Dementia Study and The Consortium for the Early Identification of Alzheimer's disease - Quebec, and included older adults who were cognitive unimpaired, those with subjective cognitive decline, mild cognitive impairment, or mild Alzheimer's disease. Half of the participants in each diagnosis group were monolingual (i.e., reported knowledge of only one language) and half were multilingual (i.e., reported knowledge of 2 or more languages). Within diagnosis groups, monolinguals and multilinguals were strictly matched on age, sex, years of education, cognitive impairment, and memory function. We examined average within-network functional connectivity of the default mode network using the CONN Toolbox. We observed reduced connectivity within the default mode network for multilinguals compared to monolinguals with Alzheimer's disease. Our finding suggests greater Alzheimer's disease neuropathology for multilingual compared to monolingual participants, despite being matched on measures of cognitive impairment and memory function. Therefore, multilingual participants show evidence of greater brain resilience by way of greater cognitive reserve compared to their monolingual peers.