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A special cochlear implant has used to light to听enable deaf gerbils听to sense sound. The results suggest that optical stimulation could one day be used to treat hearing loss in people.

The method uses a technique called optogenetics,听which involves manipulating听nerve cells so they can be activated by light. The team used a virus to insert a gene for a protein that detects light into the cochlea, the snail-shaped organ in the inner ear that converts sound into electrical signals. They then implanted an optical fibre听into the cochlea to deliver light signals.

To test whether the animals could perceive these light signals as sound, the researchers trained gerbils with intact hearing before the treatment using a behavioural test called the shuttle box. The gerbils were placed in a box with two halves separated by a hurdle.

When a sound was played, the animal had six seconds to jump over the hurdle to the opposite side. If they stayed on the same side, they got a gentle electric shock through the floor. Gerbils quickly learned to avoid this by jumping over the hurdle when they heard the sound.

After having the treatment, the trained gerbils responded to light signals in the cochlea in the same way, suggesting they perceived the signal as a sound. 鈥淭his tells you there is at least some resemblance of the percept that鈥檚 generated,鈥� says team member Marcus Jeschke of University Medical Center G枚ttingen, Germany.

Come on feel the noise

One group of trained gerbils was then made deaf after having the therapy. They no longer responded to the sound stimulus, but they still responded to the light signals.

This proves that the light signals can make the gerbils hear something, but听the implant can鈥檛 currently recreate different types of sound or let them hear real sounds in their environment.

In order to restore the full richness of sounds we can experience, it will be necessary to stimulate different parts of the cochlea separately. Cochlear implants available now can do this for some patients using electrical stimulation, but the resolution of different sounds is quite poor because current spreads widely through the cochlea.

In theory, optogenetics could be used to stimulate cells more precisely, enabling better resolution. But doing this requires a large number of very small light sources to be implanted in the cochlea. The team is looking to develop micro-LED arrays that can serve this purpose.

Making a therapy like this work in humans is a distant goal, but Jeschke believes it can be done. First they have to repeat the study in primates. 鈥淚f that works, I would say we have a very good chance that it will also work in humans,鈥� he says.

Read more: This mind-reading hearing aid knows who you鈥檙e listening to

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