TOKYO – An international research team, including a group from Kyoto University, has identified a region of the brain that acts like a switch from one language to another.

The team discovered the brain was less active when noticing a series of synonyms than noticing a series of antonyms because handling of the former is easier than the latter.

Based on the finding, a series of synonyms described in two different languages – such as “fish” and “sake” (salmon in Japanese) – were shown to 24 English-German bilinguals and 11 English-Japanese bilinguals, and their brain activities were monitored using functional magnetic resonance imaging (fMRI) and positron-emission tomography (PET).

Results showed a part located deep in the cerebrum called the left caudate responded to synonyms as the languages changed. But the left caudate shows less activity, on par with the rest of the brain, when the same experiment was conducted in just one language.

The team concluded the left caudate works like a switch to control language use.

Takashi Hanakawa, a section chief at the National Center of Neurology and Psychiatry who participated in the Kyoto University team’s research, said: “There are documented cases in which trilingual people mix up languages during a conversation when his or her left caudates are damaged. And now we can explain why that happens because of this experiment.”

The team published its findings in an article in the U.S. magazine Science.

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