Katherine Ellen Foley writing for Quartz.
“Researchers recruited 17 patients who were blind from birth and 19 patients who could see, but whose eyes were covered for the experiment. They asked the participants simple algebraic equations comparing two variables, like: If 7 − 2 = x and 6 − 1 = x, is x the same? These questions increased with difficulty slightly, to using double-digit numbers, and the researchers also asked a set of non-math questions (about the meaning of two different sentences) to serve as a control.
While they asked these questions to participants, the researchers took images of their brains using functional magnetic resonance imaging to look at which parts of the brains were using more oxygen (i.e., were more active and thus required more energy). They found that blind individuals used brain cells associated with basic visual processing (like noticing color contrast) when doing math, and used more of them as the math became more difficult. Sighted patients relied only on the part of the brain understood to play a primary role in numerical processing.
Previous work has shown that when a person lacks one sense, the brain can reallocate some of the area associated with that sense for other kinds of processing: For example, some patients who are blind appear to use the visual parts of their brain when processing different sounds. This is called cross-modal plasticity.”