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El Cerebro Bilingüe/The Bilingual Brain

Dartmouth researchers find bilinguals use more areas of the brain when processing language

Dartmouth researchers have identified areas in the brain that indicate bilingualism, a finding that sheds new light on decades of debate about how the human brain's language centers may be enhanced when faced with two or more languages as opposed to only one. The study was presented at the Society for Neuroscience's annual meeting in October 14.

NIRS researchers
From left: Ioulia Kovelman G'06, Mark Shalinsky, Melody Berens, and Laura-Ann Petitto. The researchers used infrared light to study brain activity. (Photo by Joseph Mehling '69)

The researchers used an optical imaging technology called Near Infrared Spectroscopy (NIRS) as a new "microscope" into the human brain's higher cognitive capacities, and they are among the first to use the technology in this way. NIRS has been used in the detection of, for example, breast tumors and heart blood flow. The Dartmouth team used NIRS to measure changes in the brain's oxygen levels while people performed specific language and cognitive tasks.

Authors of the study are Laura-Ann Petitto, professor and chair of the Department of Education and the study's senior scientific director; Mark Shalinsky, a former postdoctoral fellow at Dartmouth and now at Massachusetts General Hospital; Ioulia Kovelman G'06, currently a postdoctoral fellow at MIT; and Melody Berens, currently a postdoctoral fellow at Dartmouth.

"NIRS provides much the same information as functional magnetic resonance imaging or 'fMRI,' but has several advantages over fMRI," says Shalinsky, the study's electro-neurophysiologist. "NIRS technology is quiet, small, and portable. ... It's child-friendly, and it tolerates a participant's body movements, which makes it ideal for studying language where participants move their mouths to speak."

The researchers examined 20 people ranging from 18 to 30 years old. Ten participants were monolingual (spoke only English), and ten were bilingual (spoke both English and Spanish from around birth). The NIRS showed similar increased brain activity across all people in the brain's classic left-hemisphere language regions when they were speaking in only one language (that is, in "monolingual mode"), involving the left Broca's area and left dorsolateral prefrontal cortex (DLPFC), brain areas key to language and verbal working memory, respectively.

When bilinguals were simultaneously processing each of their two languages and rapidly switching between them (in "bilingual mode"), they showed increased brain activity in the left and right hemisphere Broca's area, with greater activation in the right equivalent of Broca's area and the right DLPFC. This finding emerged as the key indicator of the brain's bilingual signature.

"For decades, people have wondered whether the brains of bilingual people are different from monolinguals. People also worry that the brains of bilingual children are somehow negatively impacted by early experience with two languages," explains Petitto, who also holds the John Wentworth Endowed Chair in the Social Sciences. "The present findings are significant because they show that the brains of bilinguals and monolinguals are similar, and both process their individual languages in fundamentally similar ways. The one fascinating exception is that bilinguals appear to engage more of the neural landscape available for language processing than monolinguals, which is a very good thing."

The team proposes that bilingual language processing provides a new window into the extent of what nature's neural architecture for language processing could be, if only we used it. Petitto adds, "The irony is that we may find it is the monolingual that is not taking fuller advantage of the neural landscape for language and cognitive processing than nature could have potentially made available."

This research is funded by grants from the National Institutes of Health and the Dana Foundation.


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Last Updated: 12/17/08