Gray Matter Volume as Evidence for Cognitive Reserve in Bilinguals With Mild Cognitive Impairment.

BACKGROUND: Compared with monolinguals, bilinguals have a later onset of mild cognitive impairment (MCI) and Alzheimer disease symptoms and greater neuropathology at similar cognitive and clinical levels. The present study follows a previous report showing the faster conversion from MCI to Alzheimer disease for bilingual patients than comparable monolinguals, as predicted by a cognitive reserve (CR). PURPOSE: Identify whether the increased CR found for bilinguals in the previous study was accompanied by greater gray matter (GM) atrophy than was present for the monolinguals. METHODS: A novel deep-learning technique based on convolutional neural networks was used to enhance clinical scans into 1 mm MPRAGEs and analyze the GM volume at the time of MCI diagnosis in the earlier study. PATIENTS: Twenty-four bilingual and 24 monolingual patients were diagnosed with MCI at a hospital memory clinic. RESULTS: Bilingual patients had more GM loss than monolingual patients in areas related to language processing, attention, decision-making, motor function, and episodic memory retrieval. Bilingualism and age were the strongest predictors of atrophy after other variables such as immigration and education were included in a multivariate model. DISCUSSION: CR from bilingualism is evident in the initial stages of neurodegeneration after MCI has been diagnosed.

Bilingualism as a Contributor to Cognitive Reserve: What it Can do and What it Cannot do.

In the absence of effective pharmacological interventions for the prevention of dementia, attention has turned to lifestyle factors that contribute to cognitive reserve. Although cognitive reserve cannot prevent the occurrence of disease, the trajectory is different for high reserve and low reserve patients, giving more time for independent living to high reserve individuals. We argue that lifelong bilingual experience meets the criteria for an experience that confers cognitive reserve, although neural reserve, a related concept, is more difficult to validate. Bilingual patients show symptoms at a later stage of disease and decline more rapidly than comparable monolingual patients. These patterns are considered in terms of evidence from behavioural, imaging and epidemiological studies. Finally, the role of bilingualism in protecting against symptoms of some forms of dementia are discussed in the context of other protective factors and the limits of this reserve approach in dealing with the consequences of dementia.

Poorer clinical outcomes for older adult monolinguals when matched to bilinguals on brain health.

Previous studies have reported bilingualism to be a proxy of cognitive reserve (CR) based on evidence that bilinguals express dementia symptoms ~ 4 years later than monolinguals yet present with greater neuropathology at time of diagnosis when clinical levels are similar. The current study provides new evidence supporting bilingualism's contribution to CR using a novel brain health matching paradigm. Forty cognitively normal bilinguals with diffusion-weighted magnetic resonance images recruited from the community were matched with monolinguals drawn from a pool of 165 individuals in the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. White matter integrity was determined for all participants using fractional anisotropy, axial diffusivity, and radial diffusivity scores. Propensity scores were obtained using white matter measures, sex, age, and education as predictive covariates, and then used in one-to-one matching between language groups, creating a matched sample of 32 participants per group. Matched monolinguals had poorer clinical diagnoses than that predicted by chance from a theoretical null distribution, and poorer cognitive performances than matched bilinguals as measured by scores on the MMSE. The findings provide support for the interpretation that bilingualism acts as a proxy of CR such that monolinguals have poorer clinical and cognitive outcomes than bilinguals for similar levels of white matter integrity even before clinical symptoms appear.

Conversion of Mild Cognitive Impairment to Alzheimer Disease in Monolingual and Bilingual Patients.

PURPOSE: Conversion rates from mild cognitive impairment (MCI) to Alzheimer disease (AD) were examined considering bilingualism as a measure of cognitive reserve. METHODS: Older adult bilingual (n=75) and monolingual (n=83) patients attending a memory clinic who were diagnosed with MCI were evaluated for conversion to AD. Age of MCI and AD diagnoses and time to convert were recorded and compared across language groups. PATIENTS: Patients were consecutive patients diagnosed with MCI at a hospital memory clinic. RESULTS: Bilingual patients were diagnosed with MCI at a later age than monolingual patients (77.8 and 75.5 y, respectively), a difference that was significant in some analyses. However, bilingual patients converted faster from MCI to AD than monolingual patients (1.8 and 2.8 y, respectively) resulting in no language group difference in age of AD diagnosis. This relationship held after accounting for education, cognitive level, immigration status, and sex. DISCUSSION: The findings suggest that greater cognitive reserve as measured by language status leads to faster conversion between MCI and AD, all else being equal.

Cultural Context as a Biasing Factor for Language Activation in Bilinguals.

Two studies investigated how cultural context and familiarity impact lexical access in Korean-English bilingual and English monolingual adults. ERPs were recorded while participants decided whether a word and picture matched or not. Pictures depicted versions of objects that were prototypically associated with North American or Korean culture and named in either English or Korean, creating culturally congruent and incongruent trials. For bilinguals, culturally congruent trials facilitated responding but ERP results showed that images from both cultures were processed similarly. For monolinguals, culturally incongruent pairs produced longer RTs and larger N400s than congruent items, indicating more effortful processing. Thus, an unfamiliar culture impeded linguistic processing for monolinguals but facilitated it for bilinguals familiar with that culture. Study 2 presented images that were more or less familiar and both groups replicated the pattern for monolinguals in Study 1. Therefore, in Study 1 monolinguals responded to familiarity but bilinguals responded to culture.

Differential Allocation of Attention During Speech Perception in Monolingual and Bilingual Listeners.

Attention is required during speech perception to focus processing resources on critical information. Previous research has shown that bilingualism modifies attentional processing in nonverbal domains. The current study used event-related potentials (ERPs) to determine whether bilingualism also modifies auditory attention during speech perception. We measured attention to word onsets in spoken English for monolinguals and Chinese-English bilinguals. Auditory probes were inserted at four times in a continuous narrative: concurrent with word onset, 100 ms before or after onset, and at random control times. Greater attention was indexed by an increase in the amplitude of the early negativity (N1). Among monolinguals, probes presented after word onsets elicited a larger N1 than control probes, replicating previous studies. For bilinguals, there was no N1 difference for probes at different times around word onsets, indicating less specificity in allocation of attention. These results suggest that bilingualism shapes attentional strategies during English speech comprehension.