As far as the brain is concerned, all languages are pretty much the same. Whether the conversation is in German or English or Japanese, recent research suggests that fluent speakers use the same set of brain regions to make sense of what's being said. But if there's really just a single language circuit, how do bilingual people make sure it's only used for one language at a time? A study in tomorrow's Science hints at a possible answer.
Studies of bilingual people have found that the same brain regions, particularly parts of the left temporal cortex, are similarly activated by both languages. But there must be some part of the brain that knows Deutsch from English, reasoned cognitive neuroscientist Cathy Price at University College London. Price, along with German and Japanese colleagues, used functional magnetic resonance imaging and positron emission tomography to search for a language switch in the brains of German-English and Japanese-English bilingual volunteers.
The researchers showed the volunteers pairs of words one after another, for example "trout" followed by "salmon." In this case, the words are similar in meaning, and language regions in temporal cortex responded weakly to the second word, as if recognizing that "salmon" is nothing new. The same regions responded similarly to equivalent words in different languages, firing weakly to "salmon" after seeing the German equivalent "lachs." As previous work suggested, these regions of the temporal cortex seem to care about the meaning of words, regardless of the language.
But a region deep in the brain, the left caudate did register the change in language, responding strongly to "salmon" when preceded by "lachs," but only weakly when preceded by "trout." The left caudate picked up the switch for other equivalent German-English word pairs, as well as for Japanese-English pairs, the researchers found. Together with case studies of bilingual patients with damage to the left caudate--who are prone to switch languages involuntarily--the findings suggest that this part of the brain helps control the language in use, Price says.
The study is especially compelling because the results held up in both bilingual groups and with two imaging techniques, says Daniela Perani of Vita-Salute San Raffaele University in Milan, Italy. The work is "an important contribution to understanding the bilingual brain," agrees Michael Chee, a cognitive neuroscientist at SingHealth, a public research institute in Singapore. While much of the research on language has focused on the cortex, Chee says the new findings suggest that areas such as the caudate, tucked deep inside the brain, may have important roles too.