Researchers have provided further evidence that bilingualism may contribute to cognitive reserve and delay the onset of dementia of the Alzheimer’s type (DAT). A study published in the Journals of Gerontology Series B focused on the association between bilingualism and amnestic mild cognitive impairment (aMCI)—the common transition stage between normal aging and DAT. Specifically, the researchers examined the impact of bilingualism on the age of onset in patients with different subtypes of aMCI—single- or multiple-domain aMCI.
Patients diagnosed with aMCI have memory problems not severe enough to warrant a diagnosis of dementia. Single-domain aMCI patients experience memory deficits only, whereas multiple-domain aMCI patients exhibit memory problems and may also have impaired executive functions, language, or visuospatial ability. The study results indicate that only in cases of single-domain aMCI, bilingual patients were diagnosed at an age four and a half years older that of monolinguals. For multiple-domain aMCI patients, bilinguals were slightly younger than their monolingual counterparts. These findings indicate that bilingualism selectively protects cognitive functioning in single-domain aMCI, which is the subtype of aMCI most specifically associated with progression to DAT. The association between single-domain aMCI and DAT may reflect a compensatory advantage for single-domain aMCI patients where contributions from other brain systems (e.g., the frontal region) compensate for the cognitive losses associated with dementia (e.g., executive functioning). Unlike single-domain aMCI patients, impairment occurs directly in the frontal regions for multiple-domain aMCI patients, potentially eliminating any frontally based compensatory advantage.
Ossher L, Bialystok E, Craik F, et al. The effect of bilingualism on amnestic mild cognitive impairment. The Journals of Gerontology, Series B: Psychological Sciences and Social Sciences, 68, 8–12. DOI:10.1093/geronb/gbs038