A new study by a team of researchers headed by Dr. Ehud Zohary of the Department of Neurobiology at the Alexander Silberman Institute of Life Sciences at the Hebrew University of Jerusalem provides a better understanding of this phenomenon through closer examination of how and where information is processed in the brains of blind people. An article on his work appears in the current online edition of Nature Neuroscience magazine. It is believed that this work could open a window towards future enhancement of the quality of life for blind people.
Humans, like other primates, rely primarily on vision to direct their behavior. The areas devoted to vision constitute some 25 percent of the human brain. The prevailing thought up to now was that the loss of vision due to blindness renders these regions useless. New evidence, however, shows that the "unemployed" occipital cortex in the brain -- which usually functions in connection with vision -- is utilized in the blind for other purposes.
For example, neuroimaging techniques have shown that the occipital cortex of congenitally blind people is active during Braille reading, indicating that this so-called "sight" region of the brain becomes reoriented for information processing connected with the sense of touch.
Yet, Braille reading involves more than just fine tactile judgments, since reading involves language and memory processes as well. Using functioning imaging (fMRI) in the congenitally blind, Zohary, together with his doctoral students Amir Amedi and Noa Raz, found that extensive regions in the occipital cortex are activated not only during Braille reading, but also during performances of verbal memory tasks, such as recalling a list of abstract words.
One of these activated regions is the primary visual cortex, or V1, which is the central gateway for visual information processing in the normal human brain. In contrast, no such verbal memory-related activation was found in V1 of a sighted control group. This V1 activation, unique to the blind, was accompanied by superior verbal memory skills for the blind as a group, compared to their sighted peers. The test shows that the greater the occipital activation, the higher the scores in the verbal memory tests.
Zohary's research leads him to conclude that in congenital blindness, the visual cortex undergoes a dramatic reorganization and is recruited for high-level cognitive functions. There is evidence that this "conversion" is much more limited in people blinded at later stages in life.
Zohary says that his study opens a window for better understanding of cortical plasticity in brain systems, a crucial step in seeking to improve treatment for neurodegenerative diseases. Once researchers know more about how the cortical reorganization takes place -- and how to advance this process by proper training -- it may be possible to give blind people cognitive advantages that will serve them throughout life.
It is important to note, however, that due to the limitations of the fMRI technique, the actual neuronal mechanisms underlying memory cannot be addressed using neuroimaging, and therefore further complementary studies will be necessary, involving observation of laboratory animals performing similar behavioral tasks.