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A stroke took her braille
Brain imaging had shown that her visual cortex was no longer visual. It had been taken over by braille reading and hearing. After the stroke she lost both abilities, then recovered some function.
Her case fits a wider pattern. In people blind from birth, the occipital cortex at the back of the brain starts to respond to sound and to the touch of braille. Blind people who use their visual cortex this way have better auditory and touch acuity than sighted people, and perfect pitch is much more common among them. In people born without a nose or any smell structures in the brain, the areas that would have mapped smell are overtaken by touch, hearing, and sight.
The outer layer of the brain, the neocortex, works as a customized map of an individual's own experience. Someone who loses sight at 50 has less chance to repurpose that cortex than someone born blind, because the brain has already changed since infancy. The same pattern shows in a principle of neurology called the Kennard principle: if a brain injury is going to happen, it is better early in life.
Why would a blind brain give vision cortex to touch?
Without input from the eyes, the visual cortex does not sit idle. Neighboring senses send connections into it, and the cells that win those connections reorganize to serve them. Brain imaging studies by Alvaro Pascual-Leone and others found that braille reading in blind people activates the visual cortex. Temporary magnetic stimulation that disrupts that area interferes with their braille reading.
Why is perfect pitch more common in blind people?
Studies of blind musicians have reported higher rates of absolute pitch than in sighted musicians, especially among people blind from early life. One idea is that the extra cortex devoted to sound gives finer pitch memory. Early musical training matters too, since absolute pitch tends to develop in childhood. Researchers have found the pattern in several countries.
What is the Kennard principle?
Margaret Kennard, a neurophysiologist at Yale, found in the 1930s that infant monkeys recovered better from damage to the motor cortex than adult monkeys did. This became known as the Kennard principle. Later work showed the picture is more mixed, since early injuries can also cause lasting problems. Still, the young brain's greater ability to reassign tasks remains a central finding in developmental neurology.
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