When people think in a language they learned in adulthood, they employ special brain circuits not used for their native language, a study suggests.
But if adults started learning two languages in infancy, they use the same circuits for both, researchers found.
The difference appeared in a critical language centre of the brain called Broca`s area, which lies near the left ear in righthanded people.
The work appeared in the journal Nature.
It included six people who had been exposed to two languages in infancy and six who picked up a second language as adults. Their brains were scanned as they silently told themselves what they had done the previous day, thinking first in one language and then in another.
The findings fit with prior reports that in bilingual people, strokes or brain tumours can hinder ability in just one language.