Body Science

Understanding dementia and Alzheimer’s Disease, through the latest developments in research.

The bilingual brain: A mental two-timer

The bilingual brain: A mental two-timer

by MATT KWONG
Contributor

The good news: Speaking a second language keeps Alzheimer’s at bay. The bad news: Bilingualism makes it harder to test for the disease.

The bilingual brain is a mental two-timer. One moment it appears faithful to a native tongue; the next, it’s summoning a second language like it’s a mistress on speed dial.

It’s a cognitive juggling act that supports the idea that people who speak more than one language are slick multi-taskers. The probable reason, according to researchers, is their mastery of the brain’s so-called executive function. The command centre that manages judgment, attention processes and task switching also allows bilinguals to toggle freely between systems of communication.

What happens, though, to that cerebral circuitry as we age? Studies indicate that fluency in another language bolsters our neurological wiring against the damaging effects of dementia. “It’s called the ‘bilingual advantage,’” says University of Ottawa psychology professor Vanessa Taler. “There are aspects of some higher-order cognitive processes that bilinguals are better at. We’re interested in figuring out how it’s a factor contributing to cognitive reserve.”

Cognitive reserve refers to the brain’s resiliency and ability to stave off clinical diseases such as dementia that might be due to greater connectivity between brain regions. Education, exercise, diet and social interactions can help build greater reserves, according to doctors.

As we age, hallmarks for Alzheimer’s such as “senile plaques” deposit in the brain’s grey matter, Taler said. Those protein buildups can disrupt signals in the brain.“Neuroimaging methods can actually let you see the senile plaques, the atrophy,” she said. “The argument is that bilingualism helps you deal with it better.”

When a patient is being assessed in one language, we may not be getting the full picture of their abilities or impairments.

In 2010, Neurology published an analysis of clinical records that suggested bilingualism can push back the onset of Alzheimer’s symptoms by as much as five years. Last year a team of Toronto-based researchers detected the first physical evidence to support those findings, analyzing CT scans of multilingual patients, which showed that they were functioning at the same cognitive level as monolinguals even though their brains showed significantly more advanced symptoms of Alzheimer’s.

Evidence that learning two languages can, to some degree, delay the onset of the disease is of particular significance in a bilingual and multicultural country like Canada, where close to one-fifth of the population is fluent in both official languages.

But there’s a wrinkle. The very skill that helps delay cognitive impairment can also make it tricky to test. That’s where Taler’s work developing a French-English test for dementia comes in.

“We know there’s a high prevalence of bilingualism in Canada, we know there’s an increasing population that’s getting older, which is a primary risk factor of dementia, and yet we don’t actually have good norms for testing bilinguals,” she said. “This is what we’re trying to figure out.”

The project, funded by the Alzheimer Society of Canada and based in Taler’s lab at the Bruyère Research Institute in Ottawa, is working on a French-English diagnostic assessment. Part of the problem is bilinguals process language very differently than monolinguals, so they can’t be assessed with the same baselines Ellen Bialystok, a York University psychology professor and leading expert on bilingualism and cognitive aging, said it’s well established that there are “major significant vocabulary differences between monolinguals and bilinguals.”

Most bilinguals tend to have more streamlined vocabularies, split between both languages, and perform worse on language tasks than people fluent in only one language. Bilinguals may at times have less robust word power in both languages because their cognitive capacities for storing that much information gets maxed out.

Further, one language may be more impaired than another as Alzheimer’s progresses, explained Laura Moretta, a speech therapist and assistant professor at Université Laval who is collecting francophone data for Taler’s project.

“Bilinguals can access one language and then the other, but when they have a problem in the brain, they’re not affected in the same way,” she said.

For example, some stricken with Alzheimer’s may forget more of one language than the other. “That’s why, when a patient is being assessed in one language, we may not be getting the full picture of their abilities or impairments,” added Shanna Kousaie, a post-doctoral fellow at the Bruyère who is assisting Taler.

As for which words fade from cognitively impaired patients’ memories first, they tend to be recently learned terms or least-used words. Proper nouns such as names usually slip away as language function deteriorates. Those names may get replaced by more vague pronouns like “him” or “her.”

Taler added there is some evidence of “a disadvantage” for “biological kinds” of words, such as names for animals, possibly due to confusion over similarities in semantic features — many living creatures have four legs and fur, for instance.

She expects to have a working model of the computerized adaptive testing for French and English bilinguals finished in two years. In the meantime, her lab will gather data from 400 people to create algorithms for the test, which would present images such as a helicopter, jacket or window for a patient to identify using whichever language the subject chooses. Based on the responses—right or wrong, French or English, and the breadth of the vocabulary available—an algorithm would determine the next slide, with an adjusted difficulty level.

The test would have to be adapted for different language combinations, such as Cantonese and English, or Arabic and French.

“A bilingual has a lower vocabulary size in each language just due to being bilingual,” said Taler. “That might lead you to think there’s a problem, but it’s not because their language skills are inferior. It’s because they’re managing two languages.”

When Taler tested control subjects in a “choose your own language” scenario, 30 per cent of about 120 participants performed worse than subjects who were asked to respond in their stronger language. Two languages jockeying for words could cancel each other out, causing the participant to draw a blank, she theorized.

 

Matt Kwong is a writer based in Atlanta, Georgia, and Toronto, Canada



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