Researchers have found that the brains of people who grow up bilingual process the two languages differently from those who learn a second tongue later in life. Bilingual children appear to store both languages in the same part of a brain region, while people who become bilingual in adulthood put language ability into different cubbyholes. The findings, reported in tomorrow's issue of Nature, may help educators better evaluate language learning strategies, and they should help brain surgeons avoid damaging a person's native language area.
For years, neurosurgeons have suspected that languages might be stored in different parts of the brain--after an injury or seizure, a bilingual person can lose one language but retain the other. To better understand this phenomenon, Joy Hirsch and her colleagues at the Memorial Sloan-Kettering Cancer Center in New York City studied two groups of bilingual people: early bilinguals who learned a second language while growing up, and late bilinguals who learned as adults. As the subjects thought of a story in their native tongue and then in a second language, the researchers used magnetic resonance imaging (MRI) to monitor brain activity. Because body movement distorts an MRI image, the subjects did not speak, but imagined what they would have said.
The mute storytelling in the native tongue lit up several brain sections, including Broca's region, which is thought to store grammar knowledge. When early bilinguals thought in their second language, the exact same part of Broca's region fired up. But when the late bilinguals tried it, an area 9 millimeters away turned on. This confirms that two languages can be stored in different locations, Hirsch says. "But the independence of the two languages depends on when the two languages are learned," she says. She speculates that adults may learn languages differently than children do, or perhaps the native language region gets closed off to a second tongue after a certain age.
The findings are exciting, says Michael Posner, a language researcher at the University of Oregon. "If these results reflect the greater ease of second-language use among those who acquire languages early, they may provide us with ways to evaluate different methods of teaching," he says. Brain surgeons, in the meantime, will be able to use the findings right away. In removing a brain tumor, they'll know better how to avoid damaging the storage area for a patient's native language. "There are lots of different ways to go into the brain," says Hirsch, "and if you can tell the surgeon that you put a language function more at risk by going in from this direction, they'll have a real advantage."