Bilingualism helps protect the aging brain and may even postpone signs of dementia, a new review of recent studies indicates.
The
paper by Canadian researchers, published Thursday, suggests bilingual
people have higher cognitive reserves as they get older. Higher
cognitive reserve is associated with a lower risk of Alzheimer’s and
other memory-destroying dementias.
More than half the world’s
population is bilingual, the researchers write in the journal Trends in
Cognitive Sciences. But in the United States and Canada, about 20 per
cent of the population speaks a language other than English at home.
Lead
author and psychologist Ellen Bialystok, of Toronto’s York University,
had already begun accumulating evidence that the bilingual advantages
seen in children could also be found in healthy adults. In a 2004 study,
her team reported that bilingual adults, young and old, performed
better than monolinguals on “conflict tasks” – situations where people
need to ignore distracting stimuli to perform properly. (Think of
driving on a busy highway).
But, Bialystok said, she kept being asked one question: What about dementia?
So,
in a study published in 2007 involving about 200 Alzheimer’s patients,
half of whom were lifelong bilinguals, her team found that the bilingual
patients had been diagnosed 4½ years later with Alzheimers than people
who spoke only one language. Bialystock calls that difference “huge.”
Others
have recently shown that bilingual Alzheimer’s patents are better able
to cope with the disease and can function longer without showing
symptoms, even when CT scans of their brains show more advanced
“pathology” or disease.
It has to do with cognitive reserve,
Bialystok says – “a building up of resilience that comes from certain
experience that allows you to cope.
is cognitive impairment from nasty things like Alzheimer’s disease, the
finding is that [bilinguals] can appear to function for a longer time
than they otherwise would,” she said. “Cognitive reserve is an extra
resource that enables you to keep functioning.”
It’s not exactly
clear why. But one theory is that managing two different languages
boosts brain regions that are critical for general attention and
cognitive control.
“We know that if you know two languages, and
that there are two languages you could be speaking at any time, then
both of those languages are always active – they’re always kind of
‘available’ in your mind,” she said.
“That means that every time
you want to say something or understand something or write something,
there’s potential interference from the other language.”
When that happens, the brain’s executive-control system kicks in to man-age the conflict between languages.
The
executive-control system is the basis for our ability to multi-task and
to stay focused on what’s relevant and avoid distraction.
In bilinguals, that brain network gets “massive practice,” said Bialystok, a Distinguished Research Professor at York.
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