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Degree of bilingualism predicts age of diagnosis of Alzheimer's disease in low-education but not in highly educated Hispanics

Department of Psychiatry, University of California, San Diego, La Jolla, CA 92093-0948, United States.
Neuropsychologia (Impact Factor: 3.3). 12/2011; 49(14):3826-30. DOI: 10.1016/j.neuropsychologia.2011.09.041
Source: PubMed

ABSTRACT

The current study investigated the relationship between bilingual language proficiency and onset of probable Alzheimer's disease (AD) in 44 Spanish-English bilinguals at the UCSD Alzheimer's Disease Research Center. Degree of bilingualism along a continuum was measured using Boston Naming Test (BNT) scores in each language. Higher degrees of bilingualism were associated with increasingly later age-of-diagnosis (and age of onset of symptoms), but this effect was driven by participants with low education level (a significant interaction between years of education and bilingualism) most of whom (73%) were also Spanish-dominant. Additionally, only objective measures (i.e., BNT scores), not self-reported degree of bilingualism, predicted age-of-diagnosis even though objective and self-reported measures were significantly correlated. These findings establish a specific connection between knowledge of two languages and delay of AD onset, and demonstrate that bilingual effects can be obscured by interactions between education and bilingualism, and by failure to obtain objective measures of bilingualism. More generally, these data support analogies between the effects of bilingualism and "cognitive reserve" and suggest an upper limit on the extent to which reserve can function to delay dementia.

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    • "Moreover, Schweizer et al. (2012) reported comparable cognitive performance between bilingual and monolingual AD patients despite greater brain atrophy in the former. Bilingualism has also been claimed to favor CR throughout healthy aging (Bak et al., 2014), especially if high proficiency levels are attained (Gollan et al., 2011). Additional studies found that life-long bilingualism is positively associated with white matter integrity (Gold et al., 2013; Olsen et al., 2015) and gray matter density (Abutalebi et al., 2014, 2015) in several brain areas, crucially including the frontal lobes. "
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    • "Participants who felt they would obtain higher neuropsychological test scores if tested primarily in English were classified as Englishdominant and participants who preferred to be tested in Spanish were classified as Spanish-dominant. The current study applied an objective assessment of language dominance [8]. "
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    • "The results found in older adults indicate that age-related differences in performance on EC tasks are less severe in bilinguals than monolinguals (Bialystok et al., 2004). More dramatically, this cognitive advantage extends to dementia, where bilinguals show significantly later onset of symptoms for both Alzheimer's disease (Alladi et al., 2013; Bialystok et al., 2007; Craik et al., 2010) and mild cognitive impairment (Bialystok et al., 2014; Ossher et al., 2013), although in some studies this protection is restricted to specific cultural (Chertkow et al., 2010) or educational (Gollan et al., 2011) groups. "
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