09 Jan 2013

Faites attention! Mounting evidence suggests that lifelong bilingualism helps maintain youthful cognition. How? It may sustain neural efficiency as a person ages, according to a report in the January 9 Journal of Neuroscience. Researchers led by Brian Gold at the University of Kentucky, Lexington, found that bilingual adults performed better than monolinguals when switching between tasks, and expended less cortical energy making that switch. These results fit with a paper published September 2012 in the journal Cortex. Researchers led by Ellen Bialystok at York University, Toronto, Ontario, reported—somewhat counterintuitively—greater brain atrophy in AD patients with two native tongues versus those with just one, even though patients had similar levels of cognitive decline. That data suggested bilinguals do more with less brain volume, supporting the idea that they have more cognitive reserve and better withstand dementia pathology.

“The constant use of two languages during [a person's] lifetime seems to have protective effects on frontal parts of the brain that are especially susceptible to decline as we age,” said Gold.

Scientists have been unsure exactly what functional changes underscore a bilingual benefit. Previous studies suggested that bilingual adults get dementia an average of four years later than their monolingual counterparts (see Bialystok et al., 2007). In addition, they have better white matter integrity (see Luk et al., 2011). These polyglots may engage both language centers when talking, but suppress the irrelevant one (see Bialystok and Craik, 2010). That constant monitoring and switching back and forth could enhance other executive control systems, one theory goes. But what’s the functional mechanism behind the brain boost?

Gold and colleagues tackled that question by using functional magnetic resonance imaging (fMRI) to measure cortical activation while younger (~32 years) and older (~64 years) cognitively healthy adults performed a cognitive task that asked them to alternately identify the color or shape of objects. This type of “task switching” tests the cognitive control required to flexibly shift thoughts and behavior according to changing environmental demands. All the younger adults, regardless of language status, switched between color and shape tasks with the same reaction times, and activated similar brain structures. However, the story was different in older adults. In those who spoke only one language, performance slowed while they more strongly activated brain regions typically recruited for task-switching—the dorsolateral and ventrolateral prefrontal cortices as well as the anterior cingulate cortex. Bilingual adults, meanwhile, performed the task as quickly as younger participants, and activated networks in the brain to about the same extent as well.

It seems that knowing two languages imparted an ability to switch tasks with fewer resources than monolingual adults use, said Gold, suggesting that the brain worked more efficiently in bilingual speakers as they aged.

“Neuroimaging studies like this one help us to understand the reasons for differences between bilinguals and monolinguals—they use their functional circuitry in different ways,” said Bialystok, who was not involved in this work but has studied bilingualism and the aging brain. “Until very recently, we did not have good evidence for a functional mechanism.”

Gold’s results are consistent with Bialystok’s findings published last September. First author Tom Schweizer, St. Michael's Hospital, Toronto, and colleagues used computed tomography scans from 40 patients with probable AD to show that bilingual people showed greater cortical atrophy than monolinguals matched for years of education, cognitive functioning, and clinical severity. “Results suggest that if bilingual people are hit with Alzheimer’s disease pathology, they can lose more brain tissue than monolingual people, yet maintain cognitive abilities for longer,” Schweizer told Alzforum. This line of research adds to those investigating the mental prowess of musicians, taxi drivers, chess players, and others (see ARF related news story and ARF news story) to understand how neuroplasticity changes with aging. “Anything that keeps the brain active or involves learning a new skill would, in theory, have the same effect,” said Schweizer. Neither report suggests that full-grown adults should start learning a new language to stave off dementia, since they mainly examined people who spoke two languages starting early in life. However, the data do suggest other reasons to encourage dual language learning in children, Gold said—better fluency early in life and long-term aging benefits. “If we can identify variables that help us age more gracefully, that would have significant implications for the healthcare system,” he told Alzforum. Bilingualism especially interests Gold because it is unlikely that genetics plays a role. Researchers can thus study a purely environmental, modifiable cause of neuroplasticity.—Gwyneth Dickey Zakaib

Can Being Bilingual Preserve Brain Function?

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