Imaging shows the blind can see through sound

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A researcher at Georgetown University Medical Center (GUMC) in Washington, D.C., has used fMRI and PET imaging to prove blind volunteers were much better at locating sounds.

Josef Rauschecker, PhD, director of the program in cognitive and computational Sciences (PICCS) at GUMC, said he is working for a “future in which people who are blind will be able to wear eyeglasses that can translate the visual field scanned by the glasses into sound transmitted through headphones.”

That stream of sound can then be interpreted by the brain into information about where objects are located and even what they are, Rauschecker said.

Rudimentary devices like this now exist, and much of the science behind them, including how the blind brain processes sound, is based on the work of Rauschecker and his colleagues, he said. But Rauschecker said he wants to perfect the technology to develop an even a better set of “eyes” for the blind.

Rauschecker began studies into sensory adaptation several decades ago at the Max Planck Institute in Sarrbrücken, Germany, because he wanted to know what happened in the brains of humans who have amblyopia, a developmental disorder in which an otherwise normal eye does not transmit visual information to the brain.

“If the area of the brain that was to receive the information is not stimulated during an infant’s first two years, it will never respond to visual cues,” Rauschecker said. He said that he was able to show through animal studies that neurons geared for sight in the brain are taken over to help process sound if they are not used.

Rauschecker said that using fMRI can identify when tiny areas of the brain are activated because the tissue uses more oxygen than areas that are quiet. “It is astonishingly good,” Rauschecker said. “We can see activity in millimeters of the brain.”

Rauschecker and his team have used both fMRI and PET imaging of the visual cortex to prove blind volunteers were much better at locating sounds. They also studied the tactile sensory perception of those who are blind to figure out “how the brain divvies itself up to process both senses” and are now using MRI to trace the tracts of neurons responsible for these functions in new research.

“Water diffuses along neuronal fibers that interconnect different brain regions, so we can follow these trails. We have beautiful images of networks that run from the auditory cortex to the visual cortex that have never been seen before,” he said. “We want to know where the ability to hear using the visual cortex comes from because these neuronal structures normally aren’t there or are very sparse. A massive reorganization of the brain has gone on in blind people, probably from birth.”

Rauschecker said he plans to collaborate with scientists in Europe on development of sensory prostheses – the spectacles-like gadget that produces sound.

“We are trying to understand how the brains of blind people can be so plastic, and what we can do to take advantage of that,” he said. If devices for people who have always been blind are successful, Rauschecker hopes to modify them for use by those who have lost their vision later in life.