Fine-Structure-Based Models for Cochlear Implant Advancement

The research team from the Ear, Nose & Throat Clinic of the Medical University of Innsbruck (MUI) will work together with the Technical University of Munich (TUM) to improve the function of cochlear implants. An audio processor with microphones collects sound from the environment and translates this into a pattern of electrical pulses. These pulses stimulate the cochlear nerve via an electrode inserted into the cochlea and thereby bypass sensory cells that malfunction or were lost. Cochlear implant users are able to hear and understand speech. This very successful bionic device was implanted more than one million times worldwide but groundbreaking technical developments are missing. Performance still varies a lot among patients. The fact that 3500 sound perceiving sensory hair cells are replaced by 12-22 electrodes along the cochlear coil exemplifies the enormous plasticity of our brain to adapt and to extract sound information. Often stimulation channels even need to be deactivated to avoid ectopic stimulation. That is why it is so important to develop new stimulation strategies. Unfortunately, the inner ear is embedded in the hardest bone of our body so there is no direct access to do recordings from neurons in the inner ear. For engineers who design cars or aircrafts it is a matter of course to use simulation models to optimize shape before the first prototype is produced. There is a big need for such a tool also for cochlear implants but models are not precise enough. Werner Hemmert, Bai Siwei (TUM) and Rudolf Glückert (MUI) with Anneliese Schrott- Fischer will work together to improve such simulation models to predict realistic outcomes. High resolution X-ray tomography of various inner ears allows us to gather data on individual shape variabilities and compute the current spread with electrical stimulations. A deep look into the assembly of delicate structural elements and molecular components relevant for sound processing and signal propagation will create necessary data to feed our models. We will consider also pathological and age- related changes since cochlear implants are not designed for normal hearing people. The current spread simulation is then linked to matching cellular models of auditory neurons to predict which nerve cells are activated and how the impulses propagate along individual nerve cells. Results of this project will help to better understand electrical hearing with a cochlear implant and facilitate to refine cochlear implant technology.