Prof. Dr. med. Kristen Rak, Senior Physician and Deputy Director of the Clinic, as well as Senior Physician in the Implantable Hearing Systems Department, University Hospital Würzburg: A cochlear implant consists of two components. The speech processor is located outside the skull, while the implant is inserted under the skin of the skull during surgery.

The speech processor is the outermost part of the entire cochlear implant and is about the size of a hearing aid. It picks up sound waves via a microphone and converts them into electrical impulses. The electrical impulses are then transmitted through the skin, i.e., transcutaneously, to the thumb-sized implant inside the skull. The implant contains the electrode array. During the operation, this is inserted into the cochlea, i.e., the inner ear. The electrode array contains between 12 and 24 electrode contacts that can deliver electrical current. The electrode array has a diameter of approximately 0.8 millimeters and a length of up to 32 millimeters. This covers around 80 percent of the approximately 40-millimeter-long cochlea.

To understand how the system works, it is necessary to look at the function of the cochlea. In the cochlea, high-pitched sounds are perceived in the lower area and low-pitched sounds in the upper area. This is the same for everyone. If an electrode carrier is placed in the cochlea and the lower part of the cochlea is stimulated via an electrode contact, a high-pitched sound is perceived. If, on the other hand, an electrode contact located deep in the cochlea is stimulated, a low-pitched sound is perceived. This is the first dimension of our Perception: we hear high-pitched and low-pitched sounds.

Another aspect is volume. This can be adjusted by applying a high or low current to an electrode, but also by stimulating one or two adjacent contacts simultaneously. This transfers more energy and stimulates a larger area, resulting in higher perceived volumes.

The third aspect is rhythm, i.e., the speed between tones. A rhythm can be created by repeatedly stimulating a contact quickly or slowly.

Overall, this makes it possible to encode volume and rhythm. The nerve cells in the cochlea then pick up this information and transmit it to the brain via the Auditory nerve In the brain, the signals are then assembled into an auditory impression.

People with a cochlear implant must first learn or relearn how to hear. This takes time because the brain must first get used to the new electrical information. It can take up to a year or even longer before you can hear well or very well (again) with an implant.

A cochlear implant is suitable for two groups of people. On the one hand, children who were born deaf. They receive an implant on both sides at the age of 9-12 months. Their speech and hearing development then primarily takes place via the cochlear implant. On the other hand, the implant is also used for children and adults with increasing hearing loss. This group has or had a hearing impression that was sufficient for auditory perception and possibly also for speech training, and only developed hearing loss later on. This can be an advantage. However, some people find it more difficult to relearn hearing with the implant because they can compare it to their previous natural hearing.

Recorded by Stefanie Flunkert