Improving clarity of sound for cochlear implant users
Watch a 2 minute video on our optogenetics research
Why do cochlear implants need improvement?
The sound heard through a cochlear implant is very different to natural hearing.
While most people using a cochlear implant are able to understand speech and make sense of other sounds with relative ease, people can struggle to hear well if there’s a lot of background noise and music can sound distorted and often unpleasant.
Many of these issues stem from ‘current spread’. When electrodes generate an electrical pulse to stimulate the auditory nerve it spreads to stimulate the cells nearby. This results in a distorted signal being sent to the brain.
A fundamental change to the way bionic devices interact with nerves is required to overcome this limitation.
Combining light and electricity
Using light as an alternative to electrical stimulation has the potential to increase precision, as light can be easily directed. However, nerve cells in the inner ear don’t respond naturally to light.
To solve this issue, our researchers are using gene therapy to introduce light sensitive molecules into nerves to make them responsive to light.
The team has established that by combining light and electricity, genetically modified nerves in the ear could be stimulated with high precision, while retaining the efficiency of electrical stimulation.
Selectivity can also be improved, as only nerves that are genetically modified can respond to the light.
Next steps for Bionics Institute researchers
The next steps will be to continue development of a hybrid device containing light emitters and electrodes in an alternating configuration implanted with once-off gene therapy to modify the nerves with a light-sensitive ion channel.
Our researchers are also investigating how this technology can improve other medical devices where the key shortcoming is the excessive spread of electrical current away from the target nerves, or lack of selectivity leading to unwanted side-effects.
It has the potential to be applied to hearing and vision restoration, as well as deep brain stimulation and modulation of the peripheral nervous system.
Professor Paul Stoddart, Professor Michael Ibbotson, Professor Stephen O’Leary, Professor David Grayden, Professor David Garrett, Dr Patrick Ruther, Dr Anita Quigley, Dr Wei Tong, Dr Emma Brunton and James Begeng.
More information for researchers
Optical stimulation is a promising solution to the issue of spatially precise neural activation as light can provide highly confined stimulation and is not limited by conductive spread, as is electrical current. But, while optical stimulation offers the potential for selective and spatially precise neural activation, electrical stimulation remains the most efficient way to activate neural activity.
Our novel solution is to combine optical and electrical stimuli (termed hybrid stimulation) to overcome fundamental issues of neuromodulation by exploiting the spatial precision of optical stimulation while retaining the efficiency of electrical stimulation.
We were the first in the world to test this in the cochlear model. Light was used to precondition the opsin-modified neural tissue and electrical stimulation was used to stimulate, with rapid pulses and high precision.
Hybrid stimulation reduces the electrical power required for neural activation because the tissue is optically primed to reside near the stimulation threshold.
This enables the development of optical devices with integrated electrodes that are smaller and with more channels than traditional electrical devices.
We are exploring this concept in the cochlea, retina, brain and peripheral nervous systems.
WL Hart, K Needham, RT Richardson, PR Stoddart, T Kameneva (2023) Dynamic optical clamp: A novel electrophysiology tool and a technique for closed-loop stimulation. Journal of Biological Signal Processing and Control 85; 105031 https://doi.org/10.1016/j.bspc.2023.105031
EA Ajay, EP Trang, AC Thompson, AK Wise, DB Grayden, JB Fallon, RT Richardson (2023) Auditory nerve responses to combined optogenetic and electrical stimulation in chronically deaf mice. Journal of Neural Engineering 20; 026035 https://doi.org/10.1088/1741-2552/acc75f
Richardson, R.T., Thompson, A.C., Wise, A.K. et al. Viral-mediated transduction of auditory neurons with opsins for optical and hybrid activation. Sci Rep 11, 11229 (2021). https://doi.org/10.1038/s41598-021-90764-9
Alex C Thompson et al 2020. Hybrid optogenetic and electrical stimulation for greater spatial resolution and temporal fidelity of cochlear activation. J. Neural Eng. 17 056046 DOI: 10.1088/1741-2552/abbff0
Richardson, R., Ibbotson, M,. Thompson, A., Wise, A., & Fallon, J. (2020) Optical stimulation of neural tissue. Healthcare Technology Letters. DOI:https://doi.org/10.1049/htl.2019.0114
William L Hart et al (2020) Combined optogenetic and electrical stimulation of auditory neurons increases effective stimulation frequency—an in vitro study. J. Neural Eng. 17 DOI: 10.1088/1741-2552/ab6a68