Being bilingual produces changes in the anatomy of the brain, scientists said on Wednesday in finding that could explain why children are so much better than adults at mastering a second language.

They found that people who speak two languages have more gray matter in the language region of the brain. The earlier they learned the language, the larger the gray area.

“The gray matter in this region increases in bilinguals relative to monolinguals - this is particularly true in early bilinguals who learned a second language early in life,” said Andrea Mechelli, a neuroscientist at University College London.

“The degree is correlated with the proficiency achieved.”

Learning another language after 35 years old also alters the brain but the change is not as pronounced as in early learners.

“It reinforces the idea that it is better to learn early rather than late because the brain is more capable of adjusting or accommodating new languages by changing structurally,” Mechelli said.

“This ability of the brain decreases with time.”

Mechelli and his team used structural brain imaging to compare the size of the gray matter in the brains of 25 monolinguals, 25 early bilinguals who learned a second language before the age of five and 33 late bilinguals.

All the volunteers in the study, which is described in the science journal Nature, were native English speakers of comparable age and education.

In the early bilinguals, the gray matter in the left inferior parietal cortex was larger than in the monolinguals or the bilinguals learned a second language between the ages of 10-15.

“By looking at the size of the change (in the brain) I can tell whether someone is very proficient or not because the bigger the change the better the proficiency,” said Mechelli.

Grey matter in the brain is made up of neurons, or brain cells. The scientists do not know whether the change in bilinguals means there is an increase in the size of the cells, the number of cells or the connections between them.

“The next step would be to understand the change better at a small-scale level,” according to Mechelli.

He and his colleagues are planning further studies with people who have difficulty learning languages to see if their brain behaves differently.

They also plan to study speakers of several languages to determine whether the increase in gray matter is proportional to the number of languages .