Nov. 28, 2001 CHICAGO (Nov. 27) -- Deaf people sense vibration in the part of the brain that other people use for hearing – which helps explain how deaf musicians can sense music, and how deaf people can enjoy concerts and other musical events. "These findings suggest that the experience deaf people have when ‘feeling’ music is similar to the experience other people have when hearing music. The perception of the musical vibrations by the deaf is likely every bit as real as the equivalent sounds, since they are ultimately processed in the same part of the brain," says Dr. Dean Shibata, assistant professor of radiology at the University of Washington.
Shibata presented his findings at the 87th Scientific Assembly and Annual Meeting of the Radiological Society of North America (RSNA) here the week of Nov. 26.
"The brain is incredibly adaptable. In someone who is deaf, the young brain takes advantage of valuable real estate in the brain by processing vibrations in the part of the brain that would otherwise be used to process sound," Shibata says.
Shibata performed the research while on the faculty at the University of Rochester School of Medicine in New York. The deaf students in the study came from the National Technical Institute of the Deaf at the Rochester Institute of Technology. Shibata used functional magnetic resonance imaging (fMRI) to compare brain activity between 10 volunteers from the college and 11 volunteers with normal hearing. They agreed to let Shibata scan their brains while subjected to intermittent vibrations on their hands.
Both groups showed brain activity in the part of the brain that normally processes vibrations. But in addition, the deaf students showed brain activity in a golf ball-sized area, the auditory cortex, otherwise usually only active during auditory stimulation. The people with normal hearing did not show such brain activity.
"These findings illustrate how altered experience can affect brain organization. It was once thought that brains were just hard-wired at birth, and particular areas of the brain always did one function, no matter what else happened. It turns out that, fortunately, our genes do not directly dictate the wiring of our brains. Our genes do provide a developmental strategy – all the parts of the brain will be used to maximal efficiency," Shibata says.
The findings may explain how deaf people can enjoy music and how some become performers. Shibata uses an example from the National Technical Institute of the Deaf in Rochester, a college where musical productions are an important part of the deaf culture. Audience members attending musicals are provided with balloons which they can hold on their fingertips in order to "feel" the musical vibrations.
"Vibrational information has essentially the same features as sound information – so it makes sense that in the deaf, one modality may replace the other modality in the same processing area of the brain. It’s the nature of the information, not the modality of the information, that seems to be important to the developing brain."
Neurosurgeons should be aware of the findings before performing surgery on a deaf patient; in particular, a surgeon should be careful while operating around a deaf person’s auditory cortex, since it clearly does have a function, Shibata says.
In addition, Shibata says, the research is important because it suggests that it may be helpful to expose deaf children to music early in life so that their brain "music centers" may have the stimulus to develop. Similarly, tactile devices have been made to help convert speech sounds to vibrations in order to assist in communication. It might be helpful to expose young children to these devices early while their brains are still developing, rather than later, he says.
The findings are compatible with Shibata’s previous research into the flexibility and adaptability of the brain in deaf people. Last summer, Shibata published a paper in which he and colleagues showed that portions of the temporal lobe usually involved in auditory processing are much more active during certain visual tasks in deaf people.
Shibata performed his research using the same sort of MRI scanner that he uses clinically to study the brains of his patients at the University of Washington. However, with fMRI scans, the machine measures blood flow in the brain, and "lights up" to show what parts of the brain are active. The fMRI is still largely a research tool, but shows promise in helping to localize vital areas of the brain before surgery and is sometimes performed on patients at UW Medical Center.
The RSNA, based in Oak Brook, Ill., is an association of more than 30,000 radiologists and physicists in medicine dedicated to education and research in the science of radiology.
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