In 2007, a pioneering study by Canadian researchers Ellen Bialystok, Fergus Craik and Morris Freedman obtained results that were relayed around the world (see here). It concerned the development of dementia, that is disorders that impact memory, language, motor and spatial skills, problem solving and attention. They examined the medical records of a number of patients with dementia at a memory clinic in Toronto, half of whom were bilingual, and they found that the age of onset of the symptoms was 4.1 years later for that group than for the monolingual group. Basically, being bilingual had a protective effect in delaying the onset of dementia.
A few years later, the same researchers concentrated only on patients diagnosed with Alzheimer's disease–a common cause of dementia–and found similar results. In their conclusion, they were careful to underline that bilingualism does not prevent the development of the disease but that it appears to postpone the onset of its symptoms.
Since that set of studies, other research groups have examined the topic in the hope of confirming that speaking two or more languages does indeed have a protective effect. Morris Freedman and eight other colleagues from three different countries reported on these studies recently. They compared the Toronto results with those of two other studies, one done in Hyderabad (India) and one in Montreal. They reported that in the Hyderabad study the age of onset of dementia in a large group of patients was strikingly similar to that of the first Toronto study: 4.5 years later in bilinguals than in monolinguals.
However, and this comes as a surprise, the Montreal study failed to show the same global effect. The study did show a significant protective effect for those who spoke at least four languages, but the benefit was only marginal for those with three languages, and there was no difference between those who spoke one or two languages, unless they were immigrants. What was even more surprising was that native-born Canadian bilinguals developed Alzheimer’s disease earlier, and not later, than monolinguals.
Morris Freedman and his colleagues tried to make sense of these contradictory results. For example, they mentioned that the measure of the onset of dementia was different in Toronto and Hyderabad, on the one hand, and in Montreal, on the other. In addition, they questioned the way immigrants and nonimmigrants were defined in the Montreal study.
But the explanation may be more general than that. We have known for a long time that a person's cognitive reserve, that is the brain's resistance to cognitive decline due to aging, is associated with a number of factors such as childhood cognition, education, lifestyle including social and leisure activities, occupational status, physical exercise, etc. This explains why numerous websites dedicated to health mention exercise, mental stimulation, stress management, and having an active social life as ways, among others, of delaying dementia. So it could be, according to Morris Freedman and his colleagues, that ".... bilingualism alone is insufficient to guarantee the postponement of dementia."
This realistic statement is a step back from what people (mainly the media) took away from the early studies conducted by Ellen Bialystok. A combination of factors, instead of just one factor, would appear to have a protective effect.
Where does this leave bilingualism and its effect on later-life cognition, and not just on dementia? A study conducted by Thomas Bak and his colleagues in Edinburgh, on older citizens and not on demented patients, clearly shows that bilingualism does have a positive effect. So as to avoid the problem of different baseline characteristics in bilingual and monolingual groups (e.g. childhood intelligence), they gave a series of cognitive tests to people who had been originally tested at age 11, some 60 years beforehand. When they compared the monolinguals and the bilinguals in the group, they found that bilinguals (the majority of whom had acquired another language after age 11) performed significantly better than predicted from their baseline cognitive abilities, whereas monolinguals did not.
I asked Ellen Bialystok to comment on this result, and it is worth quoting parts of her answer: "A prevailing problem in conducting research on bilingualism is the difficulty of disentangling cause and effect: did people develop certain skills because they were bilingual or did they become bilingual because of their advantages in those skills? As much as we try to control the research, that question persists. The study by Bak and colleagues goes a long way in addressing that issue. ... It is not definitive evidence for causality, but it is the closest anyone has come to tracing the emergence of bilingual advantages in cognition to just the experience of being bilingual."
In sum, bilingualism does appear to have a positive effect on later-life cognition, as do other factors that have been known about for a much longer time.
For a full list of "Life as a bilingual" blog posts by content area, see here.
Photo of a nurse and an elderly lady from Shutterstock.
Bialystok, E., Craik, F., and Freedman, M. (2007). Bilingualism as a protection against the onset of symptoms of dementia. Neuropsychologia, 45, 459-464.
Freedman, M., Alladi, S., Chertkow, H., Bialystok, E., Craik, F., Phillips, N., Duggirala, V., Bapi Raju, S., and Bak, T. (2014). Delaying onset of dementia: Are two languages enough? Behavioural Neurology, Article ID 808137, http://dx.doi.org/10.1155/2014/808137
Bak, T., Nissan, J., Allerhand, M. & Deary, I. (2014). Does bilingualism influence cognitive aging? Annals of Neurology, 75(6), 959-963.
Woumans, E., Santens, P., Sieben, A., Versijpt, J., Stevens, M. & Duyck, W. (2015). Biingualism delays clinical manifestation of Alzeimer's disease. Bilingualism: Language and Cognition, 18(3), 568-574.
François Grosjean's website.