Scientists studied young recruits at the Swedish Armed Forces Interpreter Academy who learned a new language at a very fast pace, going from having no knowledge of a language such as Arabic, Russian or Dari to speaking it fluently in the space of 13 months.
Measured against a control group of university students who also studied intensively but in subjects other than languages, the researcher found specific parts of the brains of the language students grew.
The parts that increased in size were the hippocampus, a deep-lying brain structure involved in learning new material and spatial navigation, and three areas in the cerebral cortex.
"We were surprised that different parts of the brain developed to different degrees depending on how well the students performed and how much effort they had had to put in to keep up with the course," said Johan Martensson, a researcher in psychology at Lund University.
Students with greater growth in the hippocampus and areas of the cerebral cortex related to language learning had better language skills than the other students, the researchers said.
Some previous research has suggested Alzheimer's disease has a later onset in people who are bilingual or multilingual.
"Even if we cannot compare three months of intensive language study with a lifetime of being bilingual, there is a lot to suggest that learning languages is a good way to keep the brain in shape," Martensson said.