A number of the conditions that cause hearing loss for our patients cannot be reversed which is frustrating for our hearing specialists. Damage to the tiny, very sensitive hair cells of the inner ear is among the more prevalent reasons for hearing loss. The work of these hair cells is to vibrate in response to sound waves. What we call hearing are the translations of these vibrations into electrical energy, which is then sent to the brain.
The sensitivity of these tiny hair cells allows them to vibrate in such a manner, and thus enables us to hear, but their very sensitivity makes them extremely fragile, and susceptible to damage. The hair cells of the inner ear can sustain damage from exposure to high decibel sounds (causing noise-induced hearing loss, or NIHL), by certain medications, by infections, and by aging. The hair cells in human ears can’t be regenerated or “fixed” once they are damaged or destroyed. Since we can’t reverse the damage, hearing specialists and audiologists turn to technology instead. We compensate for hearing loss due to inner ear hair cell damage with hearing aids and cochlear implants.
Things would be a lot easier if we humans were more like chickens and fish. In contrast to humans, some fish species and birds actually have the ability to regenerate their damaged inner ear hair cells and regain their lost hearing. Odd, but true. Chickens and zebra fish are just two examples of species that have the capacity to automatically replicate and replace their damaged inner ear hair cells, thus allowing them to fully recover from hearing loss.
Bearing in mind that this research is at a very early stage and has to date produced no proven benefits for humans, some hope may be on the horizon in the treatment of hearing loss as a results of research called the Hearing Restoration Project (HRP). Financed by a non-profit organization called the Hearing Health Foundation, this research is presently being carried out in 14 different labs in the United States and Canada.Researchers included in the HRP are trying to isolate the molecules that allow the hair cells in some animals to replicate themselves, with the eventual goal of discovering some way to enable human inner ear hair cells to do the same thing.
Because there are so many different molecules mixed up in regeneration process – some that facilitate replication, some that impede it – the researchers’ work is slow-moving and difficult. Scientists are hoping that what they learn about inner ear hair cell regeneration in avian or fish cochlea can later be applied to humans. A few of the HRP scientists are pursuing gene therapies as a way to promote such regrowth, while others are working on stem cell-based approaches.
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 one day we will be able to help humans treat their hearing loss as easily as chickens do.