One of the sometimes frustrating things about being a hearing care specialist
is that a lot of the circumstances we deal with that have caused our patients to lose their hearing can’t be reversed. For example, one of the most common causes of hearing loss is damage to the miniature, sensitive hair cells that line the inner ear and vibrate in response to sound. These vibrations are translated by the brain into what we call hearing.
The sensitivity of these tiny hair cells enables them to vibrate in such a manner, and thus makes it possible for us to hear, but their very sensitivity makes them extremely fragile, and susceptible to damage. The hair cells of the inner ear can become damaged as a result of exposure to loud noises (causing noise-induced hearing loss), by certain drugs, by infections, and by aging. Once these hair cells have been damaged in human ears, science has to date not found any way to repair or “fix” them. As a result, hearing specialists and audiologists have to deal with hearing loss technologically, using hearing aids
or cochlear implants.
This would not be the case if humans were more like fish and chickens. In contrast to humans, some bird species and fish have the ability to regenerate their damaged inner ear hair cells and regain their lost hearing. Bizarre, but true. To name 2 such species, chickens and zebra fish have been shown to have the ability to spontaneously replicate and replace inner ear hair cells that have become damaged, and as a result regain their full functional hearing.
Could hearing loss in humans be reversed? Flickers 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 useful benefits for humans have yet been established. Funded by a non-profit organization called the Hearing Health Foundation, this research is presently being conducted in 14 different laboratories in the U.S. and Canada.What the HRP researchers are trying to do is isolate the molecules that allow this replication and regeneration in animals, with the purpose of discovering some way of stimulating similar regeneration of inner ear hair cells in humans.
Because there are so many distinct compounds mixed up in regeneration process – some that assist in replication, some that hinder it – the scientists’ work is slow and challenging. Scientists are hopeful that what they learn about 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 hoping that it will bear fruit, and that someday we will be able to help humans cure their hearing loss as easily as chickens do.