Brains of Deaf People May Rewire Themselves to "Hear" When Lip-reading
November 30, 1998
By capturing stunning images of the human brain at work, researchers at the University of Rochester have provided new evidence that the brains of deaf people may "rewire" themselves in a manner that may help them communicate with hearing people. The researchers found that a part of the brain normally responsible for hearing and speech - once thought to be relatively inactive in people who are deaf - is actually bustling with activity as deaf people read lips.
The findings shed new light on the brain’s remarkable ability to assign new functions to areas of the brain once thought to be dedicated to other purposes. Further, they may guide educators in developing new strategies for teaching hearing-impaired children, and may guide neurosurgeons who perform surgery near critical brain areas on deaf patients. Dean K. Shibata, M.D., of the Department of Radiology at the University of Rochester, will reveal these findings at the 84th Annual Scientific Assembly of the Radiological Society of North America in Chicago, November 30, at 9:00 a.m.
"When a hearing person imagines a sound, some activity in the part of the brain that processes sound can be seen with Functional Magnetic Resonance Imaging (FMRI)," says Shibata. "We’re finding similar areas of activation in deaf volunteers when they lip-read. It’s almost as if the brains of these volunteers were trying to create sounds to match the lips they were reading." FMRI is a relatively new technique for imaging how the brain functions. Locally, it’s available only at the University of Rochester, where surgeons use it to determine how to remove brain tumors without injuring sensitive nearby brain tissue well in advance of the actual operation.
Eight deaf volunteers, students at the nearby National Technical Institute of the Deaf, were compared to eight hearing volunteers performing a series of visual tasks while lying within a magnetic resonance scanner. The volunteers watched a silent video of someone speaking as the scanner recorded blood flow throughout regions of each volunteer’s brain. The hearing subjects showed a relatively symmetric distribution of activity between the left and right sides of the brain, but deaf volunteers showed a surprising focus of activity on the right side, in a part of the brain called the Superior Temporal Gyrus – an area normally used to process sound and speech. The activity varied depending on the type of task performed. Both hearing and deaf volunteers who tried to identify shapes that were displayed on a screen produced the same brain activity, but lip-reading produced substantial differences.
"When a person is born deaf, the brain is able to wire itself to make sure that the parts usually used for hearing are reassigned to more useful roles," says Shibata. "This study shows that this reconfiguration is very specific. A visual task involving shape identification does not activate these "auditory" areas, but tasks involving movement and language, such as lip-reading, do." This raises the question of why lip-reading in particular is allocated to the lobe responsible for hearing. It could be that the auditory cortex has the kind of processing power needed to understand language – no matter what its form.
"The findings are preliminary, but a better understanding of deaf physiology might eventually help guide strategies for deaf education," Shibata explains. "I’m currently studying how memory works. We know that deaf children use more visual approaches to memory tasks, and this may be reflected in the way their brain is organized."
The findings of the study will help neurosurgeons plan operations on a patient who is deaf. Knowing that a deaf person may be using his or her "auditory cortex" for other functions such as vision and language, neurosurgeons may take special precautions while operating near that area of the brain.
"Understanding the neurological changes brought about by deafness is important to the medical care of deaf patients," says Shibata. "Though the brain is still mostly a mystery to us, we’re chipping away at the mystery a little at a time. Every insight brings us closer to how the mind, both deaf or hearing, works."
The National Technical Institute of the Deaf at the Rochester Institute of Technology, Rochester, New York provided assistance with subjects for this project.
Collaborating with Shibata were Drs. Takasci Yoshiura, Edmund Kwok, Jianhui Zhong, David A. Shrier and Yuji Numaguchi of the Department of Radiology at the University of Rochester.