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Areas of the brain are shown in colour where it is active as someone switches tasks. A new study shows brains of bilingual speakers don't have to work as hard as people who speak only one language.

Brian T. Gold/University of Kentucky

Brian Gold grew up confident in the value of a bilingual education when his parents placed him in a French immersion school.

Now, years after leaving Montreal and becoming a neuroscientist, Dr. Gold has helped illuminate bilingualism's role in buttressing the human brain against the ravages of old age.

While the effect has been noted before, in a new study published Tuesday in the Journal of Neuroscience, Dr. Gold and his colleagues have found that older subjects who routinely employ two languages also use less energy as they alternate between mental tasks.

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The results reinforce the idea that by continually switching between languages, bilingual speakers are helping to build up their "cognitive reserve" – the synaptic stamina that can delay the onset of dementia in later years.

It is an especially important effect to understand, said Dr. Gold, who is based at the University of Kentucky at Lexington, because, unlike other brain-protecting factors that may depend on genes, acquiring and maintaining a second language is something a person can choose.

"To the extent that we can identify lifestyle variables that can help us age successfully or gracefully, that's of high importance both for individual satisfaction and for the health care system," Dr. Gold said.

In the study, Dr. Gold's team imaged the brains of 80 subjects – half of whom were fluently bilingual – as they switched between two simple tasks, one that required them to pay attention to colour and one that required them to pay attention to shape.

For younger participants, having a second language made little difference to performance. But among the older subjects, those who were bilingual were measurably faster at the task. The images revealed which parts of their brains were most active and how much oxygen their brain cells took up during the switch, a proxy for how much energy they needed to accomplish the task.

Like well-trained athletes, the brains of the bilingual subjects were more efficient at getting the job done.

Although the differences are subtle – measured in thousandths of a second – the researchers argue they demonstrate that bilingual speakers, on average, appear to be better at retaining cognitive control in their later years. Neuroscientists associate cognitive control with both an ability to switch smoothly between mental tasks and with keeping conflicting signals at bay when the brain is trying to stay focused.

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The study adds to a growing body of evidence that reinforces the value of raising children to be fluently bilingual. "I think parents worry that one language will suffer but it turns out that the parallel systems operating together offer a hidden benefit," says Kenji Hakuta, a professor of education at Stanford University.

According to Ellen Bialystok, an expert in language and cognition at York University in Toronto who was not involved in the study, the slight edge that bilingual people exhibit may add up to years of difference when it comes to maintaining brain function.

Dr. Bialystok notes that while it is a major challenge to separate the effects of a second language from the vast number of environmental and genetic factors that can influence the aging brain, her work has shown that bilingual people "who eventually do become cognitively frail and show up at the memory clinic are, on average, significantly older" than those who are unilingual and closely matched in other respects.

Health officials have warned of a coming epidemic of dementia as the baby boom generation approaches its twilight years.

Dr. Bialystok adds that while other activities, from playing a musical instrument to doing crossword puzzles, have been invoked as good ways to keep the mind limber, bilingualism is in a different category because "you use language every minute."

For his part, Dr. Gold fears he has probably lost the protective effect of French because it slipped away from him after he left Montreal in his adolescence. He is instead banking on another positive influence: "My situation is that when I came to the States, I met a Mexican woman. I married her and now I speak Spanish."

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