Bilingualism may delay onset of dementia

Preliminary data from a study by Canadian researchers suggest that speaking two languages throughout one’s life may delay the onset of dementia by up to four years. The study, led by Ellen Bialystok, a professor of psychology at York University in Toronto, Canada, and an associate scientist at the Baycrest Research Center’s Rotman Research Institute, is published in the journal Neuropsychologia.

Bialystok and her colleagues assessed 184 cognitively impaired subjects, all of whom had been treated at the Baycrest Research Center Memory Clinic between 2002 and 2005. 132 of the subjects met the criteria used to diagnose Alzheimer’s Disease, while the remaining 52 suffered from other forms of dementia. Of these patients, 91 were monolingual and 93 were bilingual. The latter group contained speakers of 25 different languages, the most prevalent of which were Polish, Yiddish, German, Romanian and Hungarian.

Results of all the patients’ Mini-Mental State Examinations were compared, and interviews were held with the neurologists who examined the patients during their first visit to the clinic. It was found that in the monolingual group, the mean age of onset of dementia was 71.4 years, whereas, for the bilingual group, the mean age was 75.5 years. Bilingualism appeared to have no effect on the progression of dementia symptoms after onset.

ambfig.JPGPrevious work by Bialystok’s team showed that bilingual 6-year-old children, as well as bilingual adults, are more adept than monolinguists at seeing both images in ambiguous figures such as the ‘rat-man’ on the left. Attention is believed to play a role in the interpretation of ambiguous figures. It has been suggested that the greater success of bilinguals in interpreting ambiguous figures may be due to their ability to control selective attention, which in turn may reflect the necessity to maintain, and remain fluent in, two language sets.

Cognitive decline is a normal part of the ageing process, with some functions, such as attention and memory encoding and retrieval being affected more than others. The distinction between age-related cognitive decline and the various forms of dementia is unclear. There is increasing evidence that the ability to retain one’s mental abilities in the twilight years is related to the lifestyle one leads in early and mid-life. For example, a recent study showed that a curry ingredient called curcumin may prevent the accumulation of amyloid plaques associated with Alzheimer’s Disease, while a study in the current issue of Ageing suggests that people with a high level of education may actually be more inclined to cognitive impairments in later life.

So how might the ability to speak more than one language have a protective effect on the ageing brain? It is possible that bilingualism contributes to what psychologists call ‘cognitive reserve’, a hypothetical construct which may be defined as the brain’s resilience to age-related neurodegeneration, due to, for example, enhanced neuronal plasticity and the ability to compensate for neuronal cell death by using alternative regions to perform certain functions.

Bialystok and her colleagues plan to carry out further research into the relationship between bilingualism and the onset of dementia symptoms. It would also be interesting to investigate the effects of learning a second language later in life.

References:

Bialystok, E., et al. (2007). Bilingualism as a protection against the onset of symptoms of dementia. Neuropsychologia 45: 459-464.

Bialystok, E. & Shapero, D. (2005). Ambiguous benefits: the effect of bilingualism on reversing ambiguous figures. Developmental Science 8: 595-604.

Whalley, L. J., et al. (2004). Cognitive reserve and the neurobiology of cognitive ageing. Ageing Research Reviews 3: 369- 382.

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