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People born blind do math with their visual cortex

People born without sight apparently process math in their visual cortex. The findings come from a newly published Johns Hopkins study, and add support to the idea that when it comes to “nature versus nurture,” cortical development is mostly “nurture.”

Earlier research had shown that when one sense is impaired, the associated brain tissue could be “diverted” to handle input from other senses, a la Daredevil. When blind people read Braille, for example, their visual cortex becomes active, and deaf cats repurpose some auditory cortex to visually locate things in 3D space. But Marina Bedny, coauthor of the study and assistant professor of psychological and brain sciences at Johns Hopkins, wanted to know how far the repurposing could go. She chose to look at something totally unrelated to the senses: algebra.

When researchers compared fMRI scans from 17 people blind since birth to those of 18 people born with sight, they observed both groups’ occipital cortex lighting up when parsing sentences describing math problems. But then they discovered that in blind participants, their visual cortex lit up when asked to solve math problems, where sighted individuals’ cortex didn’t. And the activity scaled with the difficulty of the problems. “As the equations get harder and harder, actvity in these areas goes up,” explains Bedny.

What the study suggests is that the brain is even more adaptable than we thought. “The number network develops totally independently of visual experience,” said lead author Shipra Kanjlia, a graduate student in JHU’s Department of Psychological and Brain Sciences. “These blind people have never seen anything in their lives, but they have the same number network as people who can see.”

The study also demonstrates that the visual cortex develops completely in blind people; it doesn’t just sit there, let alone atrophy. The way it lights up in response to math problems shows that the visual cortex of blind people still gets specialized and partitioned by function, just like any other part of the brain.

Bedny, who has been publishing her work on the visual cortex for the better part of a decade, says when the findings here are taken together with earlier results, they suggest the brain as a whole is adaptable and extensible, almost modular. It could someday be possible to reroute functions from a damaged area to a new spot in the brain.

“If we can make the visual cortex do math,” Bedny said, “in principle we can make any part of the brain do anything.”

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