What does it take to help hundreds of thousands of people to hear again?
The history of cochlear implants is a fascinating story of engineering and medical innovation, interdisciplinary cooperation, persistence and passion.
Early acoustic experiments
Composer Ludwig van Beethoven (* 1770) started losing his hearing in his Thirties and ordered tailor-made ear trumpets to remedy his hearing loss. Unfortunately, these mechanical amplifiers were of no avail to the deafening composer.
The first account of stimulating the auditory system electrically dates back to the early 1800s. Alessandro Volta, who is considered the father of the modern battery, heard crackling, bubbling sounds when he performed some electrical tests on himself with a probe inserted into his ears. More than one hundred years later, the “Wever and Bray experiment”, named after two researchers, suggested that restoring absent hearing could be possible under certain conditions.
The first acoustic prostheses
The first step towards the modern cochlear implant was taken in 1957, when physicist André Djourno and otologist Charles Eyriès implanted a deaf patient in France with the first electrical prosthesis that directly stimulated the hearing nerve. The patient was able to discriminate different loudness levels but could not understand speech. The device failed soon after implantation, as did another one in a different patient. Eyriès later quit his research work due to interpersonal and ethical conflicts.
Djourno’s and Eyriès’s work motivated another pioneer of cochlear implant technology to develop an auditory prosthesis that should last longer: Dr William House, a Los Angeles-based otologist. Dr House is considered the father of CI neurotology. He implanted the first patients with single-channel cochlear implants in 1961. His results were more promising than those of the French team: his patients were able to understand a few words. Unfortunately, medical complications stemming from the technology used forced Dr House to postpone his work for several years.
The pioneers of cochlear implant research were confronted with heavy criticism 40 years ago. Audiologists and ENT doctors were highly doubtful that hearing could not be restored by means of electrical stimulations. Their stimulation patterns were just too different from neural responses of the normal hearing ear, the critics argued.
Success at last!
Yet, the cochlear implant pioneers all around the world did not give up and continued their work with determination. In the 1970s, a group of electrical engineers at Vienna Technical University, among them the young doctorate student Ingeborg Hochmair-Desoyer, was adamant to find a solution for severe hearing loss. With passion and persistence they followed the approach of a cochlear implant using more than one channel for stimulation. On December 16, 1977 their invention, a multi-channel cochlear implant, was successfully implanted by surgeon Professor Kurt Burian at Vienna’s General Hospital. The first multi-channel cochlear implant worldwide had become reality. On the other side of the world, the Australian otologist Graeme Clark followed with his version of a multi-channel cochlear implant some eight months later.
Electrical engineers were the technical pioneers of the modern cochlear implant, but surgeons and their groundbreaking research were equally important. In the late 1970s, Kurt Burian did not have any surgical instructions on cochlear implantation, so he had to find his own surgical approach. Nor did he have any imaging techniques to help him prepare for the procedure. Computer tomography and Magnet Resonance Imaging, two imaging techniques that are standard in today’s cochlear implant surgery, had not been invented then. “For the cochlear implant field, this first surgery was like the first man on the moon in 1969”, says Professor Wolf-Dieter Baumgartner, ENT specialist at Vienna’s General Hospital.
Technology on the move
In the late 1970s, cochlear implant technology was not as sophisticated as it is nowadays. It delivered sound information and helped users to understand speech with lip-reading. But technology, notably speech coding strategies, became more refined. In March 1980 Conny, a Vienna patient, became the first cochlear implant user to show significant open-set speech understanding without lip-reading. Ever since, enhanced sound coding strategies and device components have led to impressive performance and user benefits.
Benefiting those with hearing loss
With the success of cochlear implants came its commercialization. In 1990, Ingeborg Hochmair hired three employees to start the first cochlear implant manufacturing company in Europe: MED-EL. The field has been growing at an impressive pace and many specialties have developed: bilateral cochlear implantation, binaural hearing, single-sided deafness, Electro-Acoustic Stimulation, hearing preservation, drug delivery, to name just a few. The devices themselves have seen dramatic improvements in multiple areas.
While acoustic implants back in the 1960s lasted only a few weeks, recipients of modern cochlear implants boast up to 25 years of use. Reliability is of utmost importance.
For cochlear implant users, smaller is better. Only 20 years ago, body-worn speech processors gave way to behind-the-ear processors, thereby allowing users to enjoy an active lifestyle with continuous hearing. Since 2013, single-unit processors have become state of the art. Cochlear implant manufacturers have been investing a lot of research into totally implantable devices, but microphone and energy issues have yet to be solved.
Sound coding strategies
The key to better "hearing" performance are sound coding strategies. Today’s cochlear implant users gain more benefit from their implants than patients 30 or 40 years ago. Sound coding strategies, i.e. the way the sound signal is decoded and transmitted to the implant, have become more refined. Sound information can be delivered in much more detail, resulting in better hearing performance. In the very early days, understanding speech without lip-reading was a sensation. Enjoying music and using the telephone were considered impossible. But research has moved on. Nowadays, the majority of users are able to talk over the telephone, enjoy music, play music themselves, learn foreign languages and attend mainstream schools and universities.
Flexibility for preserving residual hearing
With previous generations of cochlear implants, any residual hearing a patient might have had was lost after surgery. Stiff electrode leads would destroy the delicate structures of the pea-sized cochlea. With advancements in electrode technology, electrode leads became more flexible and atraumatic. In combination with enhanced surgical techniques, chances of preserving the delicate cochlear structures and consequently residual hearing have increased considerably. Implications are far-reaching. In the mid-2000s special electrodes for people with partial deafness were introduced to the market. The concept of Electric-Acoustic Stimulation has become a big success.
The criteria for cochlear implant candidacy have become less stringent, indications have widened to include more patient groups. Thirty or forty years ago only patients with profound bilateral hearing loss were eligible for cochlear implantation. In 1996, the first bilateral implantation was performed. Again, a concept that had been heavily criticized had proved successful. In 2019, simultaneous bilateral implantation in small children as young as 12 months is considered state of the art. Hearing with two ears is the natural way to hear. And what about people who only have good hearing in one ear? Similar to bilateral implantation, critics doubted that the brain would be able to process natural acoustic and electric information simultaneously. Again, innovative researchers came up with a solution. In 2013 cochlear implantation for people with single-sided deafness was approved, improving their quality of life dramatically.
Cochlear implants have come a long way. Many research fields, such as drug delivery to the cochlea and genetic screening, are waiting to be explored. These challenges will be tackled by future pioneers who are driven by passion, by personalities who won’t be disheartened by setbacks and by innovators who persevere.