I was sitting outside one day, and absorbing all of the sounds that I was hearing, from the rustle of leaves in the wind to the faint barking of a dog from a nearby park. My cochlear implant allows me to hear those sounds. This brings about the question of how does a cochlear implant work?
To explain that, you should know how the inner ear works and the levels of hearing loss.
How do we hear?
The ear can be broken up into three major parts:
- Outer ear – the outside part of the ear and the external auditory canal.
- Middle ear – dividing the outer ear and the middle ear is the eardrum. The middle ear consists of three bones (the ossicles) that connect and transmit sound waves.
- Inner ear – consists of the cochlea (contains the nerves for hearing), the vestibule and the semicircular canals (both contain the receptors for balance).
Sound waves (also called vibrations) travel down the external auditory canal and hit the eardrum, which vibrates. The vibration from the eardrum moves through the ossicles, which amplifies the sound and sends the sound waves to the inner ear and into the cochlea (the snail shaped organ). The cochlea has thousands of tiny hair cells – the nerves for hearing.
Once the sound waves reach the cochlea, they are converted into electrical impulses, which the auditory nerve sends to the brain and translates into sound.
Degrees of hearing loss
Everyone hears a different level of sound depending on their degree of hearing loss. To be a candidate for the cochlear implant, you must have a severe or profound level of hearing loss. This is determined through a variety of hearing tests and the results are shown on an audiogram.
Hearing loss is measured in decibels hearing level (dBHL) – the softest level that you can hear.
The four levels of hearing loss are:
- Mild: hearing loss is between 25-39 dBHL. You will have difficulty following speech in noisy situations.
- Moderate: hearing loss is between 40-69 dBHL. You will have difficulty following speech without a hearing aid.
- Severe: hearing loss is between 70-89 dbHL. You will need powerful hearing aids or an implant.
- Profound: hearing loss is from 90 dBHL. You will need to rely on lip-reading, sign language and/or an implant.
What is a Cochlear Implant?
A cochlear implant is an electronic device that replaces the work of damaged parts of the cochlea to provide sound signals to the brain. It bypasses the work that happens in the outer ear and the middle ear by directly stimulating the auditory nerves inside the cochlea. In short, it helps those with severe to profound hearing loss hear.
Note: hearing aids make sounds louder, while a cochlear provides sound signals to the brain.
How does it work?
A sound processor, that is powered by a battery, is worn behind the ear (or on the body depending on the version that you have), and its microphone captures, selects and arranges signals (known as sound).
The processor receives these signals and transmits them through the coil on the outside of your head to the implant. The implant converts these signs into electrical impulses and sends them along the electrode array placed inside the cochlea.
The electrode array will collect these electrical impulses, stimulate the cochlea’s hearing nerves, and will send them to the auditory areas of the brain where they will be interpreted as sound.
For more information on how cochlear implants work, check out this video here.
Who is a candidate?
Cochlear implants can help those who:
- Have moderate to profound hearing loss in both ears.
- Have profound hearing loss in one ear and normal hearing in the other.
- Receive little benefit from hearing aids.
A common question to those interested in getting a cochlear implant is how successful will the implantation be? The answer to that is, it depends.
It is difficult to determine how successful a cochlear implant recipient will be after implantation. Several factors to be considered are:
- Age at implantation (typically, the younger, the better)
- Duration of profound deafness (the shorter the duration, the better)
- Patient’s willingness to learn ‘how to hear again’ afterwards
The idea of an electronic implantable device was born by Graeme Clark in 1967. The concept was explored, innovated and finally put to test test in 1977 on Mona Anderson, the first recipient of a bone conduction hearing implant. From that point on, the cochlear implant evolved and its technology has made leaps and bounds from when it first began.
To learn more about the history of the cochlear implant, visit here.