The findings may explain why Albert Einstein said that he saw his equations as "clear images", whereas other mathematicians have reported calculating in words not pictures.
A study of people bilingual in English and Russian showed that the brain approaches a maths problem in two ways.
Scientists, led by Stanislav Dehaene, of the Inserm research centre near Paris, and Elizabeth Spelke of the Massachusetts Institute of Technology, found that asking question in a language which was not used in teaching the maths delayed the responses by a second - but only when the problem involved an exact calculation.
The research, published in the journal Science, found that exact calculations activated the left frontal lobe of the brain, known to be associated with words, whereas estimated numbers involved the left and right parietal lobes, known to be responsible for visual-spatial information and for finger control.
When brains don't count,
Review, page 9