Brains of blind people store visual information

William Atkins
Friday, 23 May 2008 07:42

Science - Biology

According to a California/Washington study, the brains of people, who have regained their vision, are able to regain at least some of their original ability to process visual information, even after years of blindness.

The article “Visual Motion Area MT+/V5 Responds to Auditory Motion in Human Sight-Recovery Subjects” was published in the May 2008 issue of the Journal of Neuroscience (volume 28, page 5141).

Its authors are Melissa Saenz, Alexander G. Huth, and Christof Koch (all from Computation and Neural Systems, California Institute of Technology (CalTech), Pasadena, California, U.S.A.); Lindsay B. Lewis (Department of Psychology, University of California at San Diego, La Jolla, California, U.S.A.), and Ione Fine (Department of Psychology, University of Washington, Seattle, Washington, U.S.A.).

The team, led by postdoctoral researcher Saenz and biology researcher Koch, knew that only a very small number of people have regained their vision from surgery. However, the ophthalmological community is working on retinal implants and gene therapies that one day could restore vision to many blind people.

Thus, the researchers wanted to know if the brains of people, who had been given their sight partially back from surgery, could still interpret visual signals from the eyes after years of blindness.

The medical community knew that when a person goes blind the portion of the brain assigned to vision, is reassigned to other duties, such as the senses of touch, speech, and sound.

Saenz stated, "Previous studies had shown that a variety of new sensory functions move into the visual cortex when a person loses their vision, especially when vision is lost as a young child, when the brain is very adaptable.”  [CalTech news release: “Sight Recovery After Blindness Offers New Insights on Brain Reorganization”]

So, the Saenz-Koch team wanted to find out if the original parts of the brain used for vision had preserved the information it had learned while the person with sighted.

The researchers found two people whose sight was partially restored by surgery in middle age after being blinded early as children.

One subject had been blinded at the age of three years in a chemical accident. Eyesight in his left eye was partially restored through a corneal stem-cell transplant. The second subject was a 53-year-old women who had been blinded since birth because of damage to her retina and cataracts. She had the eyesight in her right eye partially restored by cataract removal.

The research team used functional magnetic resonance imaging (fMRI) to study the brain’s extrasriate visual cortex, or MT+V5, which is called the visual area V5, or the visual area MT (middle temporal)—the part of the brain used to sense (perceive) visual motion.

The two patients were shown images of moving dots and provided with a variety of sounds to hear.

The researchers found, through the fMRI scans, that both people processed both sounds and visual images within the MT+V5. In normally sighted people, those who had the use of their vision for all of their lives, the MT+V5 part of the brain processes only visual images.

However, the two people only processed motion-related sound; that is, sound that went from one ear to the other. When changes of pitch or volume were introduced, the two people did not hear them.

Saenz stated, “Our data show for the first time what happens to the new sensory responses if a blind person has the chance to see again. The sound responses didn't go away. They persisted together with the restored visual responses, even after many years with regained sight." [CalTech press release]

What are the conclusions of these researchers? Please read on.