Many of the conditions that cause hearing problems for our patients cannot be reversed which is quite frustrating for our hearing specialists. One of the main causes of hearing loss, for example, is damage to the tiny hair cells in our inner ears that vibrate in reaction to sound waves. What we call hearing are the translations of these vibrations into electrical impulses which are sent to and interpreted in the brain.
These hair cell structures have to be really small and sensitive to do their jobs correctly. It is precisely because they are small and sensitive that they are also easily damaged. The hair cells of the inner ear can become damaged as a result of exposure to high decibel noises (causing noise-induced hearing loss), by certain drugs, by infections, and by aging. Once these hair cells are damaged in human ears, science has as yet not found a way to repair or “fix” them. Since we can’t reverse the damage, hearing specialists and audiologists turn to technology instead. We make up for hearing loss due to inner ear hair cell damage with hearing aids and cochlear implants.
This would not be true if humans were more like chickens and fish. That may seem like an odd statement, however it is true, because – unlike humans – some fish and birds can regenerate inner ear hair cells, thereby regaining their hearing once it has become lost. Chickens and zebra fish are just two examples of species that have the capacity to spontaneously replicate and replace their damaged inner ear hair cells, thus permitting them to fully recover from hearing loss.
While it is vital to mention at the outset that the following research is in its early stages and that no practical benefits for humans have yet been achieved, significant breakthroughs in the treatment of hearing loss may come in the future from the groundbreaking Hearing Restoration Project (HRP). This research, funded by the not for profit Hearing Health Foundation, is presently being conducted in 14 labs in the U.S. and Canada. Working to isolate the molecules that allow the replication and regeneration in some animals, HRP researchers hope to find a way to enable human hair cells to do the same.
Because there are so many different molecules mixed up in regeneration process – some that assist in replication, some that impede it – the researchers’ work is slow and difficult. 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 pursuing gene therapies as a way to promote such regrowth, while others are working on using stem cells to accomplish the same goal.
As mentioned before, this work is still in its very early stages, but we join with others in wishing that it will be productive, and that someday we will be able to help humans cure their hearing loss as easily as chickens do.