Mae West, the noted actress, sex symbol and wit, once said, "I speak two languages, Body and English." While West was evidently adept at speaking both simultaneously, most bilinguals are neurologically incapable of speaking more than one language at a time. Scientists long assumed multilingual people used distinct areas of the brain—one for each language—but mounting evidence indicates that polyglots use only one area for all the languages they speak. The brain must therefore transition between multiple "modes" in order for the speaker to switch languages while continuing to use the same section of the brain for language processing.
A new study led by University College London neurologist Jenny Crinion pinpointed the left caudate—an area of the brain known for its role in motor control—as the area responsible for controlling language and preventing the speaker from switching between dialects at inopportune times. Their results are published in the June 9th issue of the journal Science.
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"[Our result] highlights how this brain area is actually monitoring the fact that languages are changing, so that allows us to sort of make inferences about it playing an important role in bilingualism," said study coauthor Cathy Price, a UCL neuroscientist.
The researchers recorded the brain activity of 35 subjects presented with word pairs. The participants represented three groups of bilinguals: two groups of German/English speakers—whose brain functions were monitored by two different mechanisms, fMRI or positron emission topography—and one group of Japanese/English speakers, measured by fMRI. The words in each pair came in one of four combinations: similar meaning, same language; similar meaning, different language; different meaning, same language; and different meaning, different language. The scientists observed that only the left caudate became active when the words were either in different languages or had different meanings, indicating that this area is responsible for the change in mental state needed to switch between languages or topics.
"What we've shown is that this area is involved irrespective of the language that's being spoken," Price said. "It generalizes both to a European language, like German, and also to a different linguistic family, like Japanese."
The UCL team's finding that the left caudate is universally responsible for making a language switch jives with a 2000 case study led by Jubin Abutalebi, a neuroscientist at Vita-Salute San Raffaele University in Milan, Italy.