Among the sometimes frustrating things about being a hearing specialist is that many of the conditions we deal with that have caused our patients to lose their hearing cannot be reversed. Damage to the tiny, sensitive hair cells of the inner ear is one of the more common reasons for hearing loss. The job of these hair cells is to vibrate in response to sound waves. Our sense of hearing is the result of these vibrations being translated into electrical impulses and transmitted to the brain for decryption.
The sensitivity of these tiny hair cells allows them to vibrate in such a manner, and thus makes it possible for us to hear, but their very sensitivity makes them very fragile, and at risk of damage. Infections, certain medications, aging or exposure to high-volume sounds (resulting in noise-induced hearing loss) are all possible sources of damage. Once these hair cells have been harmed in human ears, science has to date not found a way to repair or “fix” them. Therefore, hearing professionals and audiologists have to treat hearing loss technologically, using hearing aids or cochlear implants.
This wouldn’t be the case if humans were more like fish and chickens. Unlike humans, some fish species and birds have the ability to regenerate their damaged inner ear hair cells and regain their lost hearing. Strange, but true. Chickens and zebra fish are just two examples of species that have the ability to spontaneously replicate and replace their damaged inner ear hair cells, thus permitting them to fully recover from hearing loss.
Could hearing loss in humans be reversed? Glimmers of hope are emerging from the groundbreaking research of the Hearing Restoration Project (HRP), but the research is preliminary and no practical benefits for humans have yet been achieved. The nonprofit organization, Hearing Health Foundation, is currently conducting research at laboratories in Canada and the United States Researchers included in the HRP are working to isolate the compounds that allow the inner ear hair cells in certain animals to replicate themselves, with the ultimate goal of discovering some way to enable human hair cells to do the same thing.
The research is painstaking and difficult, because so many distinct molecules either contribute to replication or hinder hair cells from replicating. Researchers are hoping that what they learn about hair cell regeneration in fish or avian cochlea can later be applied to humans. Some of the HRP researchers are working on gene therapies as a way to promote such regrowth, while others are working on using stem cells to accomplish the same goal.
As noted before, this work is still in its very early stages, but we join with others in wishing that it will bear fruit, and that someday we will be able to help humans treat their hearing loss as easily as chickens do.