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


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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    • "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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    ABSTRACT: Bilingualism is associated with enhanced executive functioning and delayed onset of mild cognitive impairment (MCI) and Alzheimer's disease (AD). Here, we investigated neuropsychological differences between mono- and bilingual patients with MCI and AD as well as the respective effects of dementia on the dominant and non-dominant language of bilinguals. 69 patients with MCI (n = 22) or AD (n = 47) and 17 healthy controls were included. 41 subjects were classified as lifelong bilinguals (mean age: 73.6; SD = 11.5) and 45 as monolinguals (mean age: 78.1; SD = 10.9). Neuropsychological performance was assessed on the CERAD-NP, the clock-drawing test, and the logical memory subscale of the Wechsler Memory Scale. Neuropsychological profiles showed only minor nonsignificant differences between mono- and bilingual subjects when compared between diagnostic groups. Bilingual MCI patients scored significantly lower on the verbal fluency and picture naming task in their dominant language than bilingual controls. Bilingual AD patients showed a reduced performance in their nondominant language when compared to bilingual MCI patients and bilingual controls (main effect language dominance: verbal fluency task p < 0.001; BNT p < 0.001). Bilingual MCI and AD patients show a similar pattern of neuropsychological deficits as monolingual patients do. The dominant language appears to be compromised first in bilingual MCI patients, while severe deficits of the nondominant language develop later in the course with manifestation of AD. These findings are important for the diagnostic work up of bilingual patients and the development of improved care concepts for bilingual patients such as migrant populations.
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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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    • "Hilchey & Klein, 2011). As already discussed, this protective advantage has been attributed to the frequent need, on the part of bilingual speakers, to switch between languages and thus to exercise inhibitory control (Festman et al., 2010; Prior & Gollan, 2011). "
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