Cochlear implants are amazing. They can vastly improve the hearing capability of people who are profoundly deaf. They work by using electrodes to stimulate nerve cells in different parts of the cochlea (the part of the inner ear which responds to sound) to provide a sensation of sound. These electrodes work in place of the sound-sensing hair cells in the cochlea, which are often damaged or absent when someone is profoundly deaf.
Cochlear implants are amazing, but not perfect
But cochlear implants are not perfect. They currently use electrical pulses to stimulate particular areas of the cochlea which respond to sounds of different pitches. But while there are usually over 3,000 hair cells in the inner ear, each responding to sounds at slightly different pitches, the cochlear implant has a maximum of around 20 electrodes. This means that a cochlear implant cannot separate out sounds as easily as the inner ear. In addition, the electrical signals produced by the electrodes are hard to focus, and can spill over into other regions of the inner ear. This means that the brain receives lower-quality information from the ear, and the sounds a person hears can be scrambled and hard to make sense of.
For people that use cochlear implants, therefore, it can be difficult for them to hear in noisy environments, and to understand complex sounds like speech and music. As a result, researchers are looking for ways to overcome this limitation in the performance of cochlear implants.
Hearing with light
From April this year, we’ve been funding a team of researchers based at the Bionics Institute, in Melbourne, Australia, led by Dr Rachael Richardson, to work on a possible solution to this problem. We’re funding them to investigate whether light could be used to stimulate the nerve cells in the cochlea – we can focus light much more accurately than electrical pulses. Theoretically, if we could replace the electrodes in a cochlear implant with light-emitting diodes (LEDs), the light they produce could be focused enough to only stimulate a very small region of the cochlea. This would allow the implant to separate out sounds according to their pitch much more accurately, and prevent the spill-over into other areas of the cochlea (you can see this illustrated in the image). This would ultimately lead to cochlear implants which are much better able to pass on accurate information about sound to the brain.
Light can be focused more tightly than electrical pulses, providing clearer signals from a cochlear implant.
Previous research has shown that we can make hearing nerve cells respond to light by introducing a gene that produces a light-sensitive protein into them (using a technique called gene therapy). Rachael and her team will be using this to investigate three exciting areas:
How will the nerve cells respond to light?
They will assess how well hearing nerve cells respond to light stimulation, electrical stimulation, as well as light combined with electrical stimulation. They will do this by presenting light and electrical pulses to nerve cells grown in a dish, as well as in the cochlea of mice. These cells (and mice) have been genetically modified so that the hearing nerve cells produce the light-sensitive protein, so that they can respond to light stimulation.
How accurate can light stimulation be?
They will investigate how far apart two beams of light need to be, so that different hearing nerve cells along the cochlea activate completely separately from each other and there is no spill-over between them.
Is it safe?
They will also determine if it is possible to safely and effectively introduce the new light-sensitive gene into a hearing nerve cell’s normal genes.
If successful, this innovative new research could greatly improve the precision of cochlear implants, allowing deaf cochlear implant users to experience more complex and accurate sound information. This step-change in cochlear implant technology could revolutionise the way that deaf people with a cochlear implant hear the world.
Find out more
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You can find out more about the research we’re funding in our biomedical research section.
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