Among the sometimes bothersome things about being a hearing care specialist
is that many of the circumstances we encounter that have caused our patients to lose their hearing can’t be reversed. Damage to the tiny, very sensitive hair cells of the inner ear is among the more common reasons for hearing loss. The task of these hair cells is to vibrate in response to sounds. These vibrations are interpreted by the brain into what we call hearing.
Unfortunately, the same sensitivity of these hair cells that allows them to respond to sound waves and translate them into electrical impulses that our brains perceive as hearing also makes them fragile, and vulnerable to damage. Infections, certain medications, aging or prolonged exposure to high-volume sounds (resulting in noise-induced hearing loss/NIHL) are all possible sources of damage. In humans, once these hair cells have become damaged or destroyed, they can’t be regenerated or “fixed.” Consequently, hearing professionals and hearing instrument specialists must use technological innovations such as hearing aids or cochlear implants to make up for hearing loss that is in essence irreversible.
This wouldn’t be the case if humans were more like chickens and fish. Unlike humans, some fish species and birds have the ability to regenerate their damaged inner ear hair cells and regain their lost hearing. Odd, but true. For reasons that are not fully understood, zebra fish and chickens(to name just 2 such species) have the ability to spontaneously replicate and replace damaged inner ear hair cells, and thus attain full functional recovery 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 at a very early stage and no practical benefits for humans have yet been established. This research, funded by the not-for-profit Hearing Health Foundation, is presently being conducted in 14 laboratories in the United States and Canada. Scientists included in the HRP are trying to isolate the molecules that allow the hair cells in some animals to duplicate themselves, with the ultimate goal of finding some way to enable human hair cells to do the same.
The research is painstaking and difficult, because so many different compounds either contribute to replication or prevent hair cells from replicating. But their hope is that if they can isolate the compounds that stimulate this regeneration process to happen in fish and avian cochlea, they can find a way to enable it to happen in human cochlea. The researchers in the various HRP labs are taking different approaches to the problem, some pursuing gene therapies, others working on the use of stem cells, nevertheless all share the exact same goal.
Although this research is still in it’s early stages, our staff wishes them quick success so that their findings can be extended to humans. Absolutely nothing would be more thrilling than to be able to offer our hearing loss patients a true cure.