Can Zebrafish Research Help Rewire the Brain of the Congenitally Deaf?

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Brain Rewiring

With the help of small, freshwater zebrafish, researchers at Oregon State University (OSU) have recently discovered that the otoferlin protein in congenitally deaf people has a mutation that causes profound deafness. They’ve also uncovered proof that this protein alters the growth and wiring of neurons that are vitally important to the central nervous system.

The otoferlin protein is responsible for encoding sounds within the sensory hair cells which are located inside the cochlea. Findings suggest that otoferlin serves as a calcium-sensitive linking protein. A mutation can weaken this link between the protein and a calcium synapse, or junction within the ear. These weaknesses are more likely to be the cause of hearing loss related to otoferlin.

A research team lead by Colin Johnson, associate professor of biochemistry and biophysics at OSU, learned that the otoferlin molecule, which was previously found to be too big to study easily, was much more manageable in zebrafish. In approximately five days this small freshwater species can mature from a cell to a swimming fish.

The cellular, genetic, and molecular levels of this particular species is very similar to that of humans, only on a smaller, more manageable scale. With their ability to mature quickly as well as the fact that they are transparent in color they are particularly useful. Add in the fact that they require only small amounts of water to be maintained and they are the most desirable option for study.

“We hope this work is a step toward treatment, and also toward better schemes for those who are deaf, for interacting with them and teaching them,” said Johnson. “People who are born deaf, their quality of life may be severely affected. They tend to drop out of high school at higher rates and generally not attain as high a level of education, and their incomes are not as great. We’re working hard on the biology of deafness and also trying to work our research into the other areas to come up with new ways of improving things.”

These findings propose that this protein mutation can also change the growth and wiring of specific neurons. They involve cells that serve as the cornerstones of the nervous system and are integral to the evolution of this delicate system.

“If you grow up without that protein, it’s not just a matter of throwing the gene back in. If you’re born deaf and grow up deaf, it seems the physical wiring of your brain is a little different,” added Johnson, putting emphasis on the need to “go beyond looking at those hair cells and look at the brain itself. Does the brain process information differently? That’s one area we need to think about.”

Findings suggest that the brains of people who are born deaf are able to rewire themselves. For congenitally deaf patients who hear almost nothing, the brain adapts to utilizing additional sensory skills such as peripheral vision and the sensation of touch. Many different areas of their brain are in play, especially the auditory cortex.

Researchers at the University of Western Ontario studied visual stimuli in cats. Using flashing lights in the periphery of their normal field of vision, they found that the auditory cortex was able to detect sounds coming from the peripheral areas. By deactivating the auditory cortex temporarily, their peripheral vision was noted to be unable to detect movement.

“The brain is very efficient and doesn’t let unused space go to waste. The brain wants to compensate for the lost sense with enhancements that are beneficial,” said Dr Stephen Lomber, who led the research.

“For example, if you’re deaf, you would benefit by seeing a car coming far off in your peripheral vision, because you can’t hear that car approaching from the side – the same with being to more accurately detect how fast something is moving.”

Armed with this information, Lomber feels that doctors could better learn how patients with cochlear implants adapt.

“If the brain has rewired itself to compensate for the loss of hearing, what happens when hearing is restored?”

The timing of this research was welcomed by Dr. Joanna Robinson, a researcher at the Royal National Institute for Deaf People (RNID).

According to Robinson, “This research supports previous findings that people who are deaf from birth have a larger visual field than hearing people. Research funded by ourselves recently showed that deaf adults can also react to objects in their peripheral vision more quickly than hearing adults, while deaf children react more slowly than their hearing counterparts.

“This indicates that it may take some time for the auditory part of the brain to make the switch to processing visual information.”

The future findings of such studies are anticipated by many in the scientific and medical fields. With these kinds of breakthroughs, there’s no telling with research will uncover.

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