Neuroscientists have been discovering mounting evidence that being fluent in more than one language protects against age-related cognitive declines. But there's still the major question: Why?

Researchers used functional magnetic resonance imaging (fMRI) to get a closer look at the brains of both bilinguals and monolinguals, comparing how their activity differs during specific tasks. This new study, published Tuesday in the Journal of Neuroscience, expands upon previous ideas that bilinguals tend to show superior task-switching abilities compared to monolinguals. The study was led by Brian Gold of the University of Kentucky in Lexington.

Methods

Scientists recruited 110 people who all took a survey about language background, abilities and frequency of usage. "Lifelong bilinguals" were defined as people who are fluent in two languages, specifically those who spoke English and another language every day since age 10 or younger. There was a variety of languages represented among the bilinguals, which adds to the strength of the experiments, said Judith Kroll, professor of linguistics and psychology at Pennsylvania State University, who was not involved in this study.

Results

Bilinguals and monolinguals scored about the same, on average, on tests of simple working memory. But in experiments where participants were switching between perceptual tasks, the older adult bilinguals were faster than the older adult monolinguals.

Generally among younger participants, performance did not appear to be related to bilingual vs. monolingual status.

"The fact that only the older bilinguals reveal these differences also demonstrates that this isn't a simple effect," Kroll said. "After all, the older lifelong bilinguals were once younger lifelong bilinguals."

The pattern of brain activity observed in adult bilinguals was similar to what the researchers saw in younger adults. Their better performance appeared to require "less activation in several frontal brain regions linked with effortful processing," the study said. In other words, the older bilinguals were using their brains more efficiently than the older monolinguals.

"This suggests that neural efficiency may represent a core underlying mechanism of the bilingual task-switching advantage in aging," the study authors wrote.

The researchers did not find significant differences in the volumes of key brain regions between monolinguals and bilinguals, suggesting that size was not a factor in performance.

Limitations and future research

As with many fMRI studies, the sample size in this series of experiments was relatively small. The cost of the fMRI process often limits the number of participants in studies of this nature. Further research with more participants should be done to confirm the results.

Based on this study, it's unclear whether starting to learn a second language later in life would give the same cognitive benefits as lifelong bilingualism. A different study could compare people who had begun language acquisition at various ages.

The cognitive benefits of being bilingual in old age, as observed in this study, could be considered analogous to brain benefits from exercise and other kinds of training seen in other research. Kroll noted that if that is the case, then perhaps the age of language acquisition isn't so important, but more research needs to be done in order to verify this.

Bottom line

Kroll said the study "makes an exciting contribution" to this line of research about the cognitive advantages of being bilingual in old age. There had been some skepticism about whether it was truly the knowledge of two languages that's linked to particular benefits in aging, or some other underlying characteristic that bilinguals have.

"We and others have suggested that bilinguals are 'mental jugglers' for whom the continuous activity of both languages imposes the demand to select the intended language, but we are still at an early stage of understanding how language experience specifically produces the sort of neural efficiency reported in this study," Kroll said.