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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    • "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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    ABSTRACT: The decline of cognitive skills throughout healthy or pathological aging can be slowed down by experiences which foster cognitive reserve (CR). Recently, some studies on Alzheimer's disease have suggested that CR may be enhanced by life-long bilingualism. However, the evidence is inconsistent and largely based on retrospective approaches featuring several methodological weaknesses. Some studies demonstrated at least 4 years of delay in dementia symptoms, while others did not find such an effect. Moreover, various methodological aspects vary from study to study. The present paper addresses contradictory findings, identifies possible lurking variables, and outlines methodological alternatives thereof. First, we characterize possible confounding factors that may have influenced extant results. Our focus is on the criteria to establish bilingualism, differences in sample design, the instruments used to examine cognitive skills, and the role of variables known to modulate life-long cognition. Second, we propose that these limitations could be largely circumvented through experimental approaches. Proficiency in the non-native language can be successfully assessed by combining subjective and objective measures; confounding variables which have been distinctively associated with certain bilingual groups (e.g., alcoholism, sleep disorders) can be targeted through relevant instruments; and cognitive status might be better tapped via robust cognitive screenings and executive batteries. Moreover, future research should incorporate tasks yielding predictable patterns of contrastive performance between bilinguals and monolinguals. Crucially, these include instruments which reveal bilingual disadvantages in vocabulary, null effects in working memory, and advantages in inhibitory control and other executive functions. Finally, paradigms tapping proactive interference (which assess the disruptive effect of long-term memory on newly learned information) could also offer useful data, since this phenomenon seems to be better managed by bilinguals and it becomes conspicuous in early stages of dementia. Such considerations may shed light not just on the relationship between bilingualism and CR, but also on more general mechanisms of cognitive compensation.
    Full-text · Article · Jan 2016 · Frontiers in Aging Neuroscience
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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.
    Full-text · Article · Feb 2015 · Journal of Alzheimer's disease: JAD
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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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    ABSTRACT: Bilingual older adults typically have better performance on tasks of executive control (EC) than do their monolingual peers, but differences in brain activity due to language experience are not well understood. Based on studies showing a relation between the dynamic range of brain network activity and performance on EC tasks, we hypothesized that life-long bilingual older adults would show increased functional connectivity relative to monolinguals in networks related to EC. We assessed intrinsic functional connectivity and modulation of activity in task vs. fixation periods in two brain networks that are active when EC is engaged, the frontoparietal control network (FPC) and the salience network (SLN). We also examined the default mode network (DMN), which influences behavior through reduced activity during tasks. We found stronger intrinsic functional connectivity in the FPC and DMN in bilinguals than in monolinguals. Although there were no group differences in the modulation of activity across tasks and fixation, bilinguals showed stronger correlations than monolinguals between intrinsic connectivity in the FPC and task-related increases of activity in prefrontal and parietal regions. This bilingual difference in network connectivity suggests that language experience begun in childhood and continued throughout adulthood influences brain networks in ways that may provide benefits in later life.
    Full-text · Article · Nov 2014 · Neuropsychologia
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