Cochlear implants currently use electrical pulses to activate the hearing nerve to enable deaf people to hear. To do this, 22 electrodes are placed along the length of the cochlea. Each individual electrode delivers electrical pulses to specific hearing nerve fibres, which enable the person to hear sound at a particular pitch (or frequency). However, the electrical pulses can spread from their allocated pitch region in one part of the cochlea, to another pitch region in another part of the cochlea. This means that sound can often seem scrambled, making it difficult to hear in noisy environments and to understand complex sounds like speech and music. This wide-spread electrical activation is a major limitation of the success of current cochlear implants.
This problem with cochlear implants could be solved by using light, instead of electrical pulses, to activate the hearing nerve in a more focussed and precise way. But for light-based stimulation to work, the hearing nerve cells must first be able to respond to light. The researchers, along with others, have previously shown that they can make the hearing nerve cells in the cochlea respond to light by adding a new gene to the cell’s normal genes (this technique is called gene therapy). Although light-based stimulation for cochlear implants is an exciting technique, we need to know whether it is clinically safe to use and whether it can significantly improve how well deaf people can hear sound compared to current electrical-based cochlear implants.
The main aim of this project is to determine whether light stimulation, either on its own or in combination with traditional electrical stimulation, can significantly improve how precisely the hearing nerve is activated and how well the cochlear implant works. To do this, the researchers will investigate three areas:
- 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.
- They will investigate how far apart two beams of light need to be presented so that different hearing nerve cells along the cochlea are activated completely separately from each other (i.e. there is no spread or overlap).
- They will determine if it is possible to safely and effectively introduce a new light-sensitive gene to the hearing nerve cell’s normal genes. They will do this using a technique called gene therapy in guinea pigs.
Cochlear implants are currently limited in the quality of sound information that they can provide to deaf people. This research will provide the information required to develop a novel light-based cochlear implant. This innovative technique could improve the precision of cochlear implants, thereby 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.