Among the sometimes frustrating things about being a hearing care specialist
is that many of the conditions we encounter which have caused our patients to lose their hearing cannot be reversed. For example, one of the most common causes of hearing loss is damage to the tiny, sensitive hair cells that line the inner ear and vibrate in response to sound. Our sense of hearing is the result of these vibrations being converted into electrical energy and delivered to the brain for decoding.
Unfortunately, the exact same sensitivity of these hair cells that allows them to respond to sound waves and translate them into electrical impulses that our brains understand as hearing also makes them fragile, and vulnerable to damage. Aging, certain medications, infections or prolonged exposure to high-volume sounds (resulting in noise-induced hearing loss) are all possible sources of damage. The hair cells in human ears can’t be regenerated or “fixed” after they are damaged or destroyed. Consequently, hearing professionals and audiologists must use technologies such as hearing aids or cochlear implants to compensate for hearing loss that is in essence irreversible.
If humans were more like fish or chickens, we’d have other options available. That may sound like an odd statement, however it is true, because – unlike humans – some birds and fish can regenerate the hair cells in their inner ears, and thus regain their hearing once it has become lost. To name 2 such species, chickens and zebra fish have been proven to have the capacity to spontaneously replicate and replace hair cells that have become damaged, thereby regaining their full functional hearing.
Keeping in mind that this research is preliminary and has as yet produced no proven benefits for humans, some hope for the treatment of hearing loss comes from research called the Hearing Restoration Project (HRP). The non-profit organization, Hearing Health Foundation, is currently sponsoring research at laboratories in the United States and Canada Scientists included in the HRP are working to isolate the molecules that allow the hair cells in certain animals to duplicate themselves, with the ultimate goal of finding some way to enable human inner ear hair cells to do the same thing.
This work is slow and demanding. Researchers need to sift through the many molecules active in the regeneration process – some of which facilitate replication while others impede it. But their hope is that if they can isolate the compounds that enable this regeneration process to happen in fish and avian cochlea, they can find a way to stimulate it to happen in human cochlea. A few of the HRP researchers are pursuing gene therapies as a way to stimulate such regrowth, while others are working on stem cell-based approaches.
Although this work is still in the preliminary stages, our office wishes them speedy success so that their findings can be extended to humans. Almost nothing would be more enjoyable than to be able to offer our hearing loss patients a true cure.