How do cochlear implants work

Cochlear implant definition

A cochlear implant can be defined as a complex yet small electronic device which helps in detecting and providing a sense of sound to the patient with severe hearing loss or who is profoundly deaf. It is used by individuals who receive limited benefit from binaural amplification. The cochlear implant consists of two major parts. One which is external and is placed behind the ear, and the second internal part which is inserted into the temporal bone surrounding the ear through surgery. These implants are made use by patients who cannot hear due to damage of auditory hair cells present in the cochlea. Since other sensory hair cannot be regenerated again, cochlear implants replace the function of the inner ear by stimulating nerve fibers in the cochlea directly.

Working of a cochlear implant

as mentioned above, the cochlear implant consists of two parts, the internal and external. The internal part is implanted into the temporal bone near the ear and has a receiver and a small electrode array. The latter (electrode) is inserted in the cochlea of the ear. The external part has a speech processor which is connected to a headpiece via a cord. The headpiece consists of a transmitting coil that is responsible to send and transmit the signal from the speech processor to the part which is inserted in the cochlea.
Both of these portions work together to change the sound from the environment into various electrical signals that are then sent to the hearing nerve. The microphone catches the sound energy and then sends the signal to the speech processor. The processor is responsible for ensuring that the signal is filtered, analyzed and is then converted into sound energy and a digital code. This digital code is then sent to the cord to the headpiece where it is then conveyed across the skin, by means of radio frequencies, to the internal receiver. The internal receiver sends the signal to the electrode array that is surgically implanted in the cochlea. These electrodes then detour the damaged parts and send a tiny electrical charge straight to the auditory nerve. The auditory nerve transfers the electrical signals to the brain where they are interpreted as sound. As long as this process sounds, it happens in a split second and the wearers feels as if this revolutionary process isn’t going on in the ear.

Cochlear implant vs Hearing aid

There is a misconception that hearing aids and cochlear implants are the same and fulfill the same purpose. However, the former is just used to amplify sounds so they can be detected by ears that are damaged and the latter works in a way that it bypasses the damaged parts and directly stimulates the auditory nerve. Children as small as 12 months can have a cochlear implant in their ears.

cochlear implant criteria
A CI-team in your hospital decides whether you or your kid is a candidate for an implant. Arguments that play a role in there decision are:

  • The candidate should almost be completely deaf in both ears and should get not enough improvement with regular hearing aids.
  • The candidate should me highly motivated. The follow-up program of the implantation and activation is intensive.
  • The candidate should have realistic expectations of what will happen after surgery and activation. A CI does not create or restore normal hearing.
  • Candidates should be examined by an ear, nose, and throat (ENT) doctor (otolaryngologist) and an audiologist for specific types of hearing tests.
  • a CT scan or MRI scan of the middle and inner ear is needed to determine the type of electrode (if possible to implant).
  • Candidates (especially children) need to be assessed by a psychologist to determine their condition.

As CI devices and surgical procedures continue to improve, the exact cochlear implant candidacy criteria will change over time.

Hybrid cochlear implant

A Hybrid CI combines two technologies into a single device: a hearing aid and a cochlear implant. Most people with hearing loss still have (some) residual low frequency hearing. A Hybrid CI has a shorter electrode array that only stimulates the end of the cochlea (the high frequency part) and preserves the low frequency part of the cochlea. This preservation of the low-frequency hearing can result in better understanding of melody and speech in noisy surroundings for CI users.

Cochlear implant success rate

The success rate of cochlear implants is very high. Variations depend on physical and psychosocial factors.
The best results were found among children who received their implant between the age of 0-3 years.
Almost all of these children show hearing and language improvement that is almost equal to children with normal hearing.
Most adults who never heard can benefit too from cochlear implants but are unlikely to understand speech because the brain Is not used to interpret sounds.

What does a cochlear implant sound like?

There are numerous videos on Youtube that contain simulations of cochlear implant for both speech and music. Before watching these videos you must be warned that the sound perception is different for each individual and that it changes overtime when the brain adjusts to the input. So there is no satisfying answer to this question.