Researchers hope that through optogenetics, they can use micro-LED lights to make better cochlear implants than those used by deaf people today.
Standard cochlear implants function by stimulating nerves using an electrode placed inside the cochlea, a tiny spiral cavity inside the ear. These work, but sounds are distorted and muffled.
That’s because people who aren’t deaf can normally discriminate between about 2000 different sound frequencies, whereas cochlear implants allow only about a dozen to be distinguished. As a result, these implants make human speech sound a bit like that of a dalek, and music can be unpleasant.
It’s hard to create cochlear implants with more frequencies, known as channels, because each extra one needs to stimulate auditory nerves at a different point along the cochlea. The fact that electricity can spread through living tissue means that frequencies merge when channels are too close to each other.
In contrast, light doesn’t spread through tissue, says Tobias Moser at the University Medical Center Göttingen in Germany. “You can focus light more conveniently than current.”
Moser and his team plan to develop an optical cochlear implant with 100 channels, using micro-LEDs as the light source. By using optogenetics – gene therapy that makes nerves sensitive to light – they hope to make much more sophisticated implants.
They have already shown that this approach works in mice when a single-channel optical implant is used. And this week, Moser announced at the Federation of European Neuroscience Societies conference in Copenhagen, Denmark, that his team had restored hearing to deaf rats with a 10-channel version of the implant.
For this technique to work, the animals first have to undergo gene therapy four weeks before the device is implanted. Using a harmless virus called adeno-associated virus, Moser’s team gave the rats a gene that made their auditory nerves become active when exposed to light.
A similar optogenetic approach is already being trialled in people as a treatment for blindness. But Moser says he and his team are some years away from testing their own technique in people, because they need to find a way to make the LEDs last longer. “First we have to demonstrate they are safe and reliable,” he said.
Martin Sumser at the Ludwig Maximilian University of Munich, Germany, thinks that some people would be willing to have gene therapy if it gave them more sensitive hearing. “There are plenty of people who are not happy with existing cochlear implants,” he says.
Moser says he is already getting enquiries from musicians, music fans and those who need to communicate with people in noisy environments.