VDE dialog: You’re one of Germany’s leading experts in cochlear implants. How exactly do these implants work?
Prof. Dr. Thomas Lenarz: A cochlear implant does the same job as our inner ear, which is a natural microphone that turns sound waves into electrical impulses. These stimulate the auditory nerve, which then carries these signals to the brain. The conversion of sound waves into electrical impulses is normally the task of what we call hair cells. In most cases of severe hearing impairment, these hair cells stop working. The cochlear implant replaces the defective cells.
How does that work in technical terms?
The cochlear implant stimulates the auditory nerve. It uses a microphone to record sound. A language processor converts the sound into electrical impulses, which are then sent to the auditory nerve by an electrode. These artificial electrical impulses are transmitted to the brain, just like the natural impulses from hair cells.
What challenges does this present?
When we hear naturally, all the different frequencies in music or speech are separated by a complex process in the cochlea, which is a spiral-shaped cavity. The individual frequencies then stimulate the auditory nerve. A cochlear implant divides the sound into frequencies using different contacts on the electrode. Different frequencies are assigned to each contact. This is where the implants have their limitations, as it’s not technically possible to go beyond a certain number of contacts. Cochlear implants currently have between 12 and 22 contacts.
How has the technology advanced in recent years?
The implants have improved significantly . We've achieved a considerable increase in the stimulation rate, for example – that's the number of impulses per second. We also have a better understanding of how speech signals are coded on the auditory nerve. Today’s cochlear implants are much better at replicating natural hearing. In the case of the electrodes, meanwhile, the technology has stayed the same because we're reliant on established materials and familiar production methods. We have to work within the current constraints of precision engineering and microtechnology.
Is this problem being addressed?
The electrode contacts need to be as close as possible to the nerve. Ideally, we'd insert them directly into the auditory nerve itself, and we’re currently working on developing a corresponding implant. That’s a big challenge in surgical terms, however, so it’s questionable whether it would be suitable as a routine procedure for surgeons around the world.
What about connectivity with regard to cochlear implants?
Cochlear implants are entirely digital systems that rely on connectivity. They are Bluetooth-enabled and support current standards, which allows for direct communication with smartphones, for example. This presents new opportunities in the field of telemedicine. Hearing tests and integration with other audio technologies are also possible. Meanwhile, patients can use apps to adjust their own systems themselves.
What benefits does this bring to the field of medicine?
The implants are electrical stimulators that enable people to test their own hearing. Using these tests, we can identify remotely whether problems are occurring and provide warnings or recommendations at an early stage. Doctors also get vast insights into the use of cochlear implants. If you combine data from many different patients, artificial intelligence can play an important role in analyzing it. This user data could be incorporated into new developments and also enable predictive models for future patients.
What about the communication between implants?
We have two ears, of course, so we’re always thinking about the best auditory system as a whole. If a patient has a cochlear implant in each ear, the devices talk to each other. A hearing aid on the other side of the head can also be calibrated to the implant. That’s no longer a pipe dream. The trend is definitely toward more connectivity. The degree to which companies are putting this into practice still varies, however.
What does the future of cochlear implants look like?
Currently, we’re just looking at the ears, but hearing actually takes place in the brain. The corresponding processes can be measured using an EEG, and parts of an EEG can help optimize the type of stimulation used on the auditory nerve. In the near future, this means cochlear implants will also come with measuring electrodes designed to be implanted on the auditory cortex. A cochlear implant will then be able to conduct an EEG. The implant could also be used to administer biological substances in the inner ear so as to reduce the physical trauma caused by the implanting process itself. The advancements are also moving toward fully implanted systems. That means the external processor will be placed inside the body to make “invisible hearing” a reality.
Prof. Dr. med. Thomas Lenarz teaches and researches at Hanover Medical School. He also founded the German Hearing Center (DHZ), which is one of the leading institutions in cochlear implants and has so far cared for over 11,000 patients. In this interview, Lenarz discusses where the technology currently stands and what advantages connectivity is bringing to ear implants.