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.
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)
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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.
By SUSAN KNAPP
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