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THE COCHLEAR IMPLANT IN A FEW QUESTIONS
THE COCHLEAR IMPLANT IN in a Few Questions
For the vast majority of people with hearing loss, hearing aids are the solution. However, for some people whose severe or profound hearing loss is caused by extensive damage to the sensory cells of the inner ear, this type of hearing aid isn’t enough. Instead, it might be time for a cochlear implant: a surgical solution that partially restores hearing by directly stimulating the auditory nerve.
How do cochlear implants work?
Cochlear implants have an internal and external piece, each with several different components. The latter's operating principle is similar to hearing aids. It has microphones to pick up ambient sounds, plus a processor and amplifier to process and amplify those sounds. Once the signal is ready, the system uses radio waves to transmit it to the internal portion. That internal portion, which is permanently implanted into the skull, consists of a receiver to receive and decode the signal, and an array of electrodes in the cochlea to stimulate the neurons that run through the inner ear. As a whole, the cochlear implant does the work of the inner hair cells, the cells that are usually responsible for transforming sounds into nerve impulses. How are cochlear implants installed?
The internal part of the device is implanted under general anaesthesia. The surgeon (ENT specialist) starts by making an incision in the skin behind the ear, then drills a hole in the skull to access the middle ear. From there, they make a second opening in the cochlea to insert the electrode array. Because the cochlea is shaped like a spiral, it’s crucial to place the array very carefully to avoid causing more trauma to the area. The entire operation usually takes one to three hours at most.
What does the rehabilitation process look like?
Once the patient has recovered from surgery, the external part of the device is turned on and adjusted by an audiologist. Initially, the sounds the patient hears can seem strange or mechanical, and it can take time to readjust to the hearing world. As the brain learns how to interpret the signals from the implant, which are different from the ones normally produced by the inner ear, many people find that the quality of the sound improves, as does their understanding of speech. The follow-up process is extremely important to make sure that the patient is using the implant properly and that they receive the best possible long-term results. During the follow-ups, a full team (including an audiologist, a speech-language pathologist, and sometimes even a psychologist or other specialist) makes sure that the patient is adjusting well.
When do cochlear implants become an option?
Cochlear implants are useful for people whose hearing loss is caused by neuropathy or the loss, absence, or dysfunction of cells in the cochlea. For example, if the hearing loss is due to a mechanical problem in the middle ear, a cochlear implant would not be a good choice. By the same token, an implant wouldn’t be helpful for someone with a severed auditory nerve, since even artificial nerve impulses wouldn’t be able to reach the rest of the auditory system. In addition, people whose auditory system has developed normally have a much better prognosis. That’s why it’s important for children who are born deaf to receive the implant as soon as possible. For the same reasons, an adult who has heard is a much better candidate than someone who has been deaf their entire life. Finally, even though techniques have become more sophisticated and significant collateral damage is fairly rare, implantation is still a surgery done under general anaesthesia. As such, the patient’s general health needs to be considered.
Talk to your audiologist if you want to learn more about cochlear implants.
François Lussier
Audioprosthetist practicing in Sherbrooke (article written in collaboration with Bianca Hallé, audiologist)
Reference - The Canadian Hard of Hearing Association.
Cochlear implants. Online. https://www.chha.ca/en/ hearing-education/cochlear-implants/. Consulted on November 10, 2020.