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Bilinguals: Of Two Minds

What happens when you learn two languages in childhood? Here's how the brain organizes speech-processing areas.

If you learned a second language as a young adult, a foreign film with subtitles may tap two speech-processing parts of your brain. Neurologist Joy Hirsch monitored the brain activity of young people as they composed sentences in their heads. They included six "early" bilingual subjects, who have known two languages since childhood, and six "late" ones, those who learned a second language no earlier than age 11. Hirsch and her colleagues at Memorial Sloan Kettering Cancer Center found that the first group showed activity in a single part of Broca's area, a region in the frontal lobe of the brain that controls speech production. But in late bilinguals, Broca's area was home to two separate sites of activity, one for each language. (Although distinct, the two regions weren't all that far apart—about a third of an inch.)

The age at which we learn a language may determine how the speech-processing areas of the brain are organized, notes Hirsch in Nature . Neural pathways forged during the language-acquisition phase of childhood might not change after the phase is over (scientists aren't sure how long it lasts). So if a second language is learned later, the brain has to store that information someplace else.