Milestone in hearing research: optogenetic cochlea implant
For the first time a gene therapy in the cochlea with optical cochlear implants was used to optogenetically activate the auditory pathway in gerbils.
Conventional hearing prostheses, cochlear implants (CI), stimulate the auditory nerve of severely hearing impaired or deaf people by applying electric currents. However, the quality of this artificial hearing is far from the quality of natural hearing. This is particularly evident in a poor speech understanding in environments with background noise. Further, the perception of music is clearly restricted. In the future, a fundamental improvement in hearing could be achieved with a cochlear implant if it was possible to activate the auditory nerve spectrally selective. Since light – in comparison to electric currents – can be better spatially confined, this would enable a highly precise activation of the auditory nerve.
Hearing researchers from Göttingen and a team of engineers from the University of Freiburg in Germany have now taken a big step towards the development of an optical cochlear implant. Since the auditory nerve does not naturally react to light, it must first be made light-sensitive through gene therapy. An animal model for human hearing loss with a genetically modified, light-sensitive auditory nerve, developed at University Medical Center Göttingen (UMG), has now been used to test a new cochlear implant for hearing with light.
Stimulation with µLEDs
In previous studies, a maximum of three optical fibers were used to optically stimulate the auditory nerve and guide light from external lasers into the cochlea. In the recent study, optical cochlear implants with 16 μLEDs (microscale light-emitting diodes) with an edge length of only 0.06 millimetres have been used for the first time to stimulate the auditory nerve in gerbils. They have been realized by integrating microscaled light-emitting diodes that are able to generate light at different sites within the cochlea independent of each other.
The results of the study prove that it is possible to stimulate the genetically modified auditory nerve using μLED cochlear implants developed specifically for this purpose. The strength of nerve cell activity scaled with the light intensity and number of simultaneously activated μLEDs. Of particular importance was the proof of high precision in the excitation of the auditory pathway, which allows a better pitch discrimination.
Further refinement is needed to improve the energy efficiency and optical properties of optical CIs. The researchers already know that lens systems can be combined with μLEDs and thus direct more light at higher precision onto the auditory nerve. They now plan to perform long-term experiments with these optical CIs in animal models to investigate their usefulness for pitch discrimination at the behavioural level, and to test the long-term stability of the approach. A first clinical study in humans is expected to be conducted in the mid-2020s.
[Alexander Dieter et al., µLED-based optical cochlear implants for spectrally selective activation of the auditory nerve, EMBO Molecular Medicine, 29.06.2020, doi: 10.15252/emmm.202012387]