The Bilingual Brain

Maureen sits in the doctor's office, where she has just received a diagnosis of Alzheimer's disease—the irreversible, progressive brain disease that slowly destroys memory and thinking skills. Also in the waiting room is Jean-Marc, who is about to see the doctor and will receive the same diagnosis. His cognitive function is about the same as Maureen's, though his symptoms appeared several years later in life.

There is one other major difference between them—Jean-Marc grew up in Québec and spent his working life in Toronto, speaking both English and French. Maureen spoke only one language.

This fictional comparison illustrates key findings of York University researcher Ellen Bialystok. Her studies have involved over 400 patients, divided into bilingual and monolingual groups at equal stages of Alzheimer's disease. She found that bilingual patients experienced the onset of symptoms about four and a half years later. She also found that bilingual patients were, on average, three to four years older when they were diagnosed.

This difference is believed to be the result of a lifetime of bilingualism, which causes the brain to operate in a different manner.

"No matter what language a bilingual person is speaking at a given moment, both languages are active in the brain," says Bialystok. "This joint activation means that bilinguals need to recruit the executive function system to pay attention to the right language. Constantly engaging this executive control function is a form of mental exercise. Bilingual people can get a little extra mileage from these cognitive networks because they have been enhanced throughout life."

Her findings have been confirmed by other studies around the world, and Bialystok's work has received extensive media coverage in major newspapers and on television news shows. She is quick to point out that being bilingual will not prevent Alzheimer's disease, but it does help patients cope with the disease for longer. Further research by Bialystok is beginning to provide some answers as to why.

She compared computed tomography (CT) scans of people with Alzheimer's disease who were bilingual with those who were monolingual. Both groups were at the same stage in their cognitive ability. For bilingual people, atrophy of grey matter in the brain area affected by Alzheimer's disease was twice as large. According to conventional wisdom, they should have had a much lower cognitive ability. However, somehow, their brains were compensating.

Further studies using diffusion tensor imaging—a magnetic resonance imaging (MRI) technique—provides the likely answer. In the bilingual group, their white brain matter—a component of the central nervous system—was larger and healthier.

"Some kind of protective effect is kicking in," says Bialystok. "The constant brain activity associated with the bilingual brain is preserving white matter and providing extra resources with which to compensate when Alzheimer's begins to strike."

These results are the first evidence that maintained white matter integrity is related to a lifelong, naturally occurring experience. This white matter integrity is providing people with a "brain reserve" that can compensate for impaired cognitive ability.

"These findings could contribute to better therapies for patients recovering from a stroke or a brain injury," says Bialystok. "There's also potential for improving education and learning; the brain has an incredible capacity for adapting and we need to know more."