Brains of the Blind Adapt
Verbal tasks are reassigned to unused visual areas of the brain
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MONDAY, June 16, 2003 (HealthDayNews) -- Rather than laying dormant, visual areas in the brains of those who are blind are reassigned to process non-visual information.
In a new study that advances the understanding of the brain's visual cortex, Israeli researchers explain that because blind people don't need to interpret visual images, the visual cortex in their brains processes verbal information instead.
"Basically, the study suggests that the visual cortex can be put to use in other non-visual tasks when the retina is dysfunctional from birth," says one of the study's authors, Ehud Zohary, a senior lecturer in the department of neurobiology at Hebrew University in Jerusalem. "It shows that the cortex is much more amenable to change than has previously been suggested."
Zohary says previous research had shown the visual cortex was active during Braille reading, but researchers believed the visual cortex was responding to the sense of touch used for Braille. The current study shows the visual cortex may instead be responding to non-sensory cues and appears to be processing verbal tasks.
For this study, published in the July issue of Nature Neuroscience, Zohary and his colleagues recruited 10 people who had been blind since birth to undergo functional magnetic resonance imaging (fMRI).
The test was broken into six different sections. One section tested verbal memory by asking the volunteers to recall a list of words they had learned. Another part of the test was called "verb generation" and the study participants were asked to come up with a verb to go with the stated noun. For example, "read" is a verb for the noun, "book." In another part of the test, the volunteers listened to words. They also had to read Braille words, and another test had them read meaningless groups of Braille letters to see if their visual cortexes were responding to touch or to the words. Finally, they also had a fMRI while they were at rest.
For comparison, the researchers also asked seven people with normal vision to complete the same tasks wearing a blindfold.
They found that in blind people, the visual cortex was most active when performing verbal memory tasks.
"The blind as a group seem to be better than their sighted peers in their verbal memory skills," says Zohary. "What is most exciting is that those individuals that show the greatest activation of their visual cortex during verbal memory tasks are the ones who are particularly good at these tasks, while others who show much less activation do much worse at those tasks. This strongly suggests that the blind take advantage of this extra cortical tissue to excel in verbal memory tasks."
Zahory says this research needs to be corroborated in future studies, but adds it's exciting to think that an area of the brain can undergo such a radical change in function.
Neurologist Dr. A. Robert Spitzer, from William Beaumont Hospital in Royal Oak, Mich., says he was surprised to see the visual cortex had taken over verbal memory tasks in the Israeli study.
"We normally think that particular areas of the brain are specifically dedicated to performing certain functions," says Spitzer. "What this is saying is that the brain can be rewired to perform completely different functions. The implication is that while the brain is making its connections, if it doesn't get any visual input, the brain makes a different set of connections."