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

Sep 19, 2016
Originally published on September 19, 2016 6:23 pm

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."

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When a person is born without sight, it changes their brain. Areas that usually process information from the eyes get rewired to do other jobs. And now there's evidence that blind people even use these visual areas to do math. NPR's Jon Hamilton reports.

JON HAMILTON, BYLINE: Marina Bedny of Johns Hopkins University wants to know how experience shapes the human brain, so Bedny's been studying people who have no experience with vision.

MARINA BEDNY: About a quarter of your brain is devoted to visual perception. And so what we can ask by working with people who are born blind is, what happens to this large part of the brain when it doesn't get its typical experience?

HAMILTON: Earlier studies found that in blind people, visual areas can be rewired to process information from other senses like hearing and touch. That's a pretty minor change, and Bedny says those studies lead to a view of the brain that assumes it can be rewired a little but not a lot.

BEDNY: It thinks of the brain as a toolkit with very particular functions, like - these are scissors; they cut, right?

HAMILTON: Bedny wasn't so sure. She wanted to know whether visual areas of the brain could do something radically different, something that had nothing to do with the senses, so she picked math.

Bedny in a team of researchers studied the brains of 17 blind people and 19 sighted people. The team used functional MRI to measure brain activity while participants were asked to solve algebra problems in their heads.

BEDNY: So they would hear something like, 12 minus three equals X. And then they would hear another equation, like four minus two equals X. And they'd have to say whether X had the same value in those two equations.

HAMILTON: Both blind and sighted people had lots of activity in two brain areas known to be involved in math, but Bedny says only the blind people also had activity in areas usually reserved for vision.

BEDNY: As the equations get harder and harder, activity in these areas goes up in a blind person. And that really suggests, yes, blind individuals appear to be doing math with their visual cortex.

HAMILTON: The results appear in the Proceedings of the National Academy of Sciences, and Bedny says they suggest the brain can rewire some areas to do just about anything. She says if that's true, it might lead to new treatments for people with injured brains.

BEDNY: So if you can't use this part of your brain 'cause you've had a stroke there, can we help you to use a different part of your brain to do the same function? And that would be really exciting.

HAMILTON: Other scientists who study brain development were surprised by the results. Melissa Libertus at the University of Pittsburgh says she never expected to see visual cortex doing algebra.

MELISSA LIBERTUS: It shows us how plastic our brain is, how flexible it is. And to see that this structure can be re-used for something very different is very surprising.

HAMILTON: Libertus says now she'd like to know precisely when a blind child's brain starts rewiring visual cortex.

LIBERTUS: In a sense, how long does the brain wait for input to come before it gives up and says, OK, let's figure out something else that we can do with as part of the brain.

HAMILTON: Libertus says knowing that could improve care for babies born with cataracts and other vision problems that can be corrected with surgery. Operating on a newborn is risky, but if surgeons wait too long, a child's visual system may not develop normally. Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.