Congenitally blind people use visual cortex in the brain to do math thinking

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Congenitally blind people are born unable to see or with severe visual impairment. This means they have little visual experience and seldom use their visual cortex to process visual stimuli, such as faces, houses, buildings, and nature.

However, a recent study conducted by Harvard University and Johns Hopkins University shows that congenitally blind people use visual cortex to solve math problems. The finding is published in PNAS.

Researchers asked 17 congenitally blind people and 19 blindfolded sighted people to solve math equations with different difficulty (e.g., 27-12 = x vs. 7 – 2 = x) and a sentence comprehension task during fMRI scanning.

They found no difference was found in the math performance between the two groups. In both blind and sighted people, brain activity in the parietal (intraparietal sulcus) and prefrontal regions was stronger in the math task than in the sentence task.

In addition, the activity in the parietal region was correlated with math difficulty, and this confirmed previous findings.

Surprisingly, in blind but not sighted people, activity in the early visual areas was also found in the math calculation task. These visual areas played a key role in visual processing in normally sighted people.

In blind people, the early visual areas and parietal region showed similar activity patterns, that is, the activity was associated with math task difficulty. Furthermore, the visual areas showed increased functional connectivity with the parietal and frontal regions activated in the math task.

Researchers suggest that our knowledge of numbers develops independently of visual experience. In blindness, the brain network of numbers colonizes parts of the visual cortex. Moreover, human cortex is highly functionally flexible early in life.


Citation: Kanjlia S, et al. (2016). Absence of visual experience modifies the neural basis of numerical thinking. PNAS, in press. doi: 10.1073/pnas.1524982113
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