Individuals proficient in more than one language automatically speak the right language in a given situation. Yet neuroimaging studies show that multiple languages rely on a common brain area, which leaves open the question of how a bilingual individual keeps different languages distinct. Now, Cathy Price, from University College London in the United Kingdom, and colleagues have identified a region of the brain, called the left caudate, that becomes activated when an individual switches from one language to another.
In the current study, which was published in the June 9 issue of Science, bilingual individuals were shown two words in rapid succession. Sometimes the words had similar meanings, such as fish and salmon. Other times they were dissimilar. Also, the two words could be in the same language or in each of the two languages in which the volunteer was fluent.
As expected, the team saw that language centers in the brain became active regardless of which language was used. However, they saw that neuronal activity in the left caudate increased when the second word had a different meaning or was in a different language.
“We found that this one region in the caudate was responding both to the meaning of language and the language itself,” says Price. She thinks the left caudate detects changes in the characteristics of words. For example, we constantly select words that are appropriate for a given context, choosing some words when talking to an adult and others when talking to a small child. If Price is correct, then when a bilingual person chooses which language to use in a particular context, he or she is using the same language control region we rely on all the time, even within a single language.