This is a Discovery Research Grant awarded to Professor Rachael Richardson at the Bionics Institute, Australia. It started in May 2025.
Background
Cochlear implants provide a sensation of hearing to those who have severe to profound hearing loss. They use electrical signals to directly stimulate the auditory, or hearing, nerve. This direct stimulation bypasses damaged parts of the cochlea (the organ of hearing) that are not working.
Part of a cochlear implant is inserted into the inner ear – this consists of a receiver that is fitted under the skin behind the ear, and an electrode array. The receiver picks up sound information from the outside world and passes it onto the electrode array. The electrode array is like a wire that carries electrical signals into the cochlea and stimulates the auditory nerve. This gives the user a sensation of hearing.
Typically, electrodes in the array are stimulated one at a time to avoid overlapping electrical currents that could otherwise ‘blur’ the signal sent to the brain. However, this means the implant cannot send information about fine changes in the timing of sound information. These changes are critical for understanding speech in background noise, locating where a sound is coming from, and the perception of pitch and timbre (the distinctive quality of a musical sound).
Since sound itself is analogue (a signal which continuously varies with time, unlike a digital signal which is made up of separate blocks of information), presenting information through the electrodes in an analogue format could provide a more accurate and natural representation of sound compared to digital stimulation. Previous research has shown that people using cochlear implants who experienced analogue stimulation reported a more pleasant sound and an improved ability to hear music.
However, analogue stimulation requires the electrodes in the array to be stimulated simultaneously, and this causes significant blurring of the sound, limiting its widespread use. The researchers have recently shown that light can be used to stimulate the hearing nerve more precisely than an electrical signal. This would require inner ear cells to be modified using gene therapy to become responsive to light, but could make it possible to send analogue signals through a cochlear implant, improving sound quality.
Aim
In this project, the researchers will investigate whether analogue light stimulation can improve the quality and accuracy of sound transmitted to the hearing nerve.
They will study deaf mice whose inner ear nerve cells have been genetically modified to respond to light. These mice will be given a cochlear implant with an electrode array that delivers either an electrical or optical (light) signal to the hearing nerve.
The researchers will compare analogue and electrical stimulation strategies to see if the analogue strategy improves the quality of hearing through the implant.
Benefit
The results from this study will show whether analogue optical stimulation can provide a better sensation of hearing through a cochlear implant than electrical stimulation. This could ultimately lead to the development of improved cochlear implant technology that brings a richer listening experience to cochlear implant users.