Cerebral plasticity and localization; mathematics, vision, numerosity

Dan Modano, Blind People Do Math In The Visual Cortex , ReliaWire:

People blind from birth appear to do math in a part of the brain typically devoted to vision, a new study has found. Researchers using functional MRI watched the visual cortex in the brains of congenitally blind people as they solved algebra problems in their heads.

The visual cortex didn’t merely respond, the researchers say. The more complicated the math, the greater the activity they saw in the vision center.

The same did not happen in the brains of sighted people with masks covering their eyes who did the same math exercises as the blind subjects.

However:

Many believe this number sense evolves from seeing the world and trying to quantify all the sights. But seeing has nothing to do with it; the study showed that the brain network behind this sort of numerical reasoning is identical in blind and sighted people.

“The number network develops totally independently of visual experience,” Kanjilia says. “These blind people have never seen anything in their lives, but they have the same number network as people who can see.”

The research article:

Shipra Kanjliaa, Connor Lanea, Lisa Feigensona, and Marina Bednya, Absence of visual experience modifies the neural basis of numerical thinking, PNAS vol. 113 no. 40 > Shipra Kanjlia, 11172–11177, doi: 10.1073/pnas.1524982113

Significance: Human numerical reasoning relies on a cortical network that includes frontal and parietal regions. We asked how the neural basis of numerical reasoning is shaped by experience by comparing congenitally blind and sighted individuals. Participants performed auditory math and language tasks while undergoing fMRI. Both groups activated frontoparietal number regions during the math task, suggesting that some aspects of the neural basis of numerical cognition develop independently of visual experience. However, blind participants additionally recruited early visual cortices that, in sighted populations, perform visual processing. In blindness, these “visual” areas showed sensitivity to mathematical difficulty. These results suggest that experience can radically change the neural basis of numerical thinking. Hence, human cortex has a broad computational capacity early in development.

Abstract: In humans, the ability to reason about mathematical quantities depends on a frontoparietal network that includes the intraparietal sulcus (IPS). How do nature and nurture give rise to the neurobiology of numerical cognition? We asked how visual experience shapes the neural basis of numerical thinking by studying numerical cognition in congenitally blind individuals. Blind (n = 17) and blindfolded sighted (n = 19) participants solved math equations that varied in difficulty (e.g., 27 − 12 = x vs. 7 − 2 = x), and performed a control sentence comprehension task while undergoing fMRI. Whole-cortex analyses revealed that in both blind and sighted participants, the IPS and dorsolateral prefrontal cortices were more active during the math task than the language task, and activity in the IPS increased parametrically with equation difficulty. Thus, the classic frontoparietal number network is preserved in the total absence of visual experience. However, surprisingly, blind but not sighted individuals additionally recruited a subset of early visual areas during symbolic math calculation. The functional profile of these “visual” regions was identical to that of the IPS in blind but not sighted individuals. Furthermore, in blindness, number-responsive visual cortices exhibited increased functional connectivity with prefrontal and IPS regions that process numbers. We conclude that the frontoparietal number network develops independently of visual experience. In blindness, this number network colonizes parts of deafferented visual cortex. These results suggest that human cortex is highly functionally flexible early in life, and point to frontoparietal input as a mechanism of cross-modal plasticity in blindness.