A CT scan showing a cochlear implant in the left ear of a guinea pig. Image: UNSW Australia Biological Resources Imaging Laboratory, NationalImaging Facility of Australia, and UNSW TranslationalNeuroscience Facility

Scientists have devised a strategy they hope will one day make bionic ears even sharper. The idea is to make neurons inside the ear sprout new branches and become more sensitive to signals from a cochlear implant.

The cochlear implant is arguably the most successful bionic device ever invented. More than 200,000 people with severe hearing loss have received one, allowing them to understand speech and hear things like barking dogs and fire alarms. But theres plenty of room for improvement.

Pitch perception is not so good, and that impacts music appreciation and hearing in a complex environment like a noisy room, said Gary Housley, a physiologist and neuroscientist at the University of New South Wales in Australia, and the senior author of a new study out today in Science Translational Medicine.

To appreciate what Housleys team did, you have to picture whats going on inside the inner ear. The bony, spiral cochlea is where sound waves get translated into the electrical language of neurons. Its essentially a coiled tube. The implant is thin like a wire, and it has an array of electrodes along its length. Surgeons thread it into the tube of the cochlea.A microphone worn on the ear converts sound into electrical signals and transmits them to the implant, thereby stimulating the auditory nerve directly and bypassing whatever part of the persons own hearing apparatus has broken down.

A cross section of the spiral tube of the cochlea shows the auditory nerve reaching up through the center. Image: Grays Anatomy, via WikiCommons

But a lot of information gets lost in the communication between the implant and the nerve.

Housley thinks one important reason is that in people with severe hearing loss, auditory nerve fibers degenerate and shrink into the bony core of the cochlea, farther away from the implant.

To try to overcome this communication breakdown, Housleys team borrowed some tricks from genetic engineering. We refer to it as closing the neural gap, he said.

Work by other scientists had suggested that growth factorschemicals that encourage neurons to grow new branchescouldimprove the performance of implants in lab animals. These studies used viruses to deliver genes encoding the growth factors, but Housleys team tried another strategy they think could be more precise.

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Genetic Tricks Could Make Bionic Ears Hear Better