When Blind People Do Algebra, The Brain's Visual Areas Light Up

People born without sight appear to solve math problems using visual areas of the brain.

A functional MRI study of 17 people blind since birth found that areas of visual cortex became active when the participants were asked to solve algebra problems, a team from Johns Hopkins reports in the Proceedings of the National Academy of Sciences.

"And as the equations get harder and harder, activity in these areas goes up in a blind person," says Marina Bedny, an author of the study and an assistant professor in the department of psychological and brain sciences at Johns Hopkins University.

In 19 sighted people doing the same problems, visual areas of the brain showed no increase in activity.

"That really suggests that yes, blind individuals appear to be doing math with their visual cortex," Bedny says.

The findings, published online Friday, challenge the idea that brain tissue intended for one function is limited to tasks that are closely related.

"To see that this structure can be reused for something very different is very surprising," says Melissa Libertus, an assistant professor of psychology at the University of Pittsburgh. "It shows us how plastic our brain is, how flexible it is."

Earlier research found that visual cortex could be rewired to process information from other senses, like hearing and touch. But Bedny wanted to know whether this area of the brain could do something radically different, something that had nothing to do with the senses.

So she picked algebra.

During the experiment, both blind and sighted participants were asked to solve algebra problems. "So they would hear something like: 12 minus 3 equals x, and 4 minus 2 equals x," Bedny says. "And they'd have to say whether x had the same value in those two equations."

In both blind and sighted people, two brain areas associated with number processing became active. But only blind participants had increased activity in areas usually reserved for vision.

The result suggests the brain can rewire visual cortex to do just about anything, Bedny says. And if that's true, she says, it could lead to new treatments for people who've had a stroke or other injury that has damaged one part of the brain.

Drugs or even mental exercises might help a patient "use a different part of your brain to do the same function," Bedny says. "And that would be really exciting."