Study with the deaf reveals brain's 'rewiring'

By capturing images of the human brain at work, researchers at the Medical Center have provided new evidence that the brains of deaf people may "rewire" themselves in a manner that may help them maximize use of their brains and assign more relevant functions to parts of the brain usually involved in hearing. 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 extremely active as deaf people read lips.

The findings shed new light on the brain's ability to assign new functions to areas of the brain once thought to be dedicated to other purposes. Further, these findings 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.

Shibata

"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)," said Dean Shibata of the Department of Radiology. "We're finding similar areas of activation in deaf volunteers when they lip-read. Perhaps there are parts of the brain specialized in the kind of rapid temporal processing used in understanding speech, and these areas can be adapted in the deaf for lip-reading."

FMRI is a relatively new technique for imaging how the brain functions. Locally, FMRI is available only at Strong Memorial Hospital, where it can be used on patients to identify critical areas of brain function and help neurosurgeons plan operations to spare these areas.

Eight deaf volunteers 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 activity 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. However, 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," said 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."

Collaborating with Shibata were Takashi Yoshiura, Edmund Kwok, Jianhui Zhong, David Shrier, and Yuji Numaguchi, all of the Department of Radiology.