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What Are Cochlear Implants?

A cochlear implant is a surgically placed device that helps a person with severe hearing loss hear sounds.
The cochlea is a snail-shaped part of the inner ear. It turns sound vibrations into electrical signals that travel along the auditory (hearing) nerve. The brain translates these signals into recognizable sounds.

A hearing aid makes sounds louder so people with hearing loss can hear.
Cochlear implants bypass damaged parts of the cochlea to stimulate the auditory nerve directly. They may help when a hearing aid can’t.

How Do Cochlear Implants Work?

Cochlear implants have:

  • A microphone and speech processor that sit outside the body. The microphone picks up sound and sends it to the processor. The processor is a minicomputer that changes the sound into digital information. Then, a transmitter sends the digital signal to the receiver/stimulator.
  • A receiver/stimulator that’s placed under skin and muscle behind the ear. This gets information from the processor. It sends electrical impulses by a thin wire to electrodes placed in the cochlea. The electrodes stimulate the auditory nerve. The message goes to the brain and the brain can use the information to recognize sounds and understand speech.
Who Can Get a Cochlear Implant?

Doctors consider cochlear implants for children under 12 months of age with profound hearing loss in both ears. Older children with serious hearing loss also may get cochlear implants.

A cochlear implant team will help decide if cochlear implants are a good option. This team includes an audiologist (hearing specialist), an ear-nose-throat (ENT) doctor, a speech therapist, a psychologist, and a social worker.

Kids being considered for the surgery will:

  • get hearing tests
  • have speech/language evaluations
  • use a hearing aid for a while to see if it helps
  • get computed tomography (CT) or magnetic resonance imaging (MRI) scans to look at the inner ear and the bones that surround it

Kids might not get the implants if:

  • Their hearing is “too good” (they can hear some sound and speech with hearing aids).
  • Their hearing loss isn’t due to a problem with the cochlea.
  • They’ve been profoundly deaf for a long time.
  • The auditory nerve is damaged or absent.

Infants and Children – Their Special Needs:

As has often been said, children are not “little adults.” They are indeed, unique, and to address their CI needs, they require an experienced clinician. Most children are unable to provide accurate feedback while the audiologist programs their cochlear implant and therefore, the clinician must take many things into account:

  • The audiologists’ past experiences with other patients
  • updated information regarding the child’s progress (from parents, therapists and teachers
  • audiometric test measures
  • observations of the child during programming
  • objective measurements (NRT/NRI, ESRT)

if age appropriate, the clinician will train the child to participate in programming (Conditioned Play Audiometry (CPA), loudness growth task.
Many of the decisions made during programming appointments come from the clinician’s knowledge and experience, rather than the child’s behavioral responses’

Mapping Trends:
Although cochlear implant maps are individualized and set according to the patient’s physiologic responses, there are trends witnessed across patient populations.

(As stated above, T level (threshold) is the least amount of electrical current necessary for a person to perceive a sound. The C or M level is the most comfortable level, or a loud but comfortable level. The CI dynamic range is defined as the difference between T and C/M levels These parameters are referred to as the patient’s “map.”)

With the Cochlear Americas Nucleus 24 device, the amount of electrical stimulation available (using default programming parameters) is between 0 and 240 clinical units (cus) and it is extremely rare to see T levels at or below 100 cus. Additionally, there are not many adult patients that have C levels above 210 cus. With the Advanced Bionics HiRes processing strategy, average M levels are between 100 cus and 300cus. More information on average stimulation levels can be found in Zwolan & Overstreet [9].

Etiology of hearing loss also appears to influence stimulation levels, possibly due to neural survival. For example, a patient deafened from meningitis may have extremely high stimulation levels, while a patient with Connexin 26 gene deficits may have extremely low stimulation levels.

When a patient’s device is initially activated, stimulation levels change frequently while the patient is learning to listen with their cochlear implant. Figure A shows how cochlear implant maps change over the first two years, as was determined on post-lingually deafened adult. As the graph shows, stimulation levels increased during the beginning of her CI experience, but eventually a plateau was seen and stimulation levels hovered in a certain clinical unit range.

One theory as to why this phenomenon exists could be — At first, the auditory system is extremely sensitive to the electrical stimulus and is learning how to manage the information. After continued use and practice, the brain adjusts (neural plasticity) and learns to effectively use the electrical input. Over time, the person requires higher stimulation levels to hear optimally, and the parameters that become the optimal map generally remain stable for many years of cochlear implant use. It is important to note that the majority of adult CI users do not have stimulation levels that continue to increase over time. If they did, the patient would eventually reach the output limits of the device and no longer benefit from their cochlear implant.

It appears that pediatric maps show higher stimulation levels over time, as compared to adult cochlear implant maps. Researchers hypothesize that children will often adapt to their program settings, even if they are set too high, and therefore, gradual increases in stimulation at subsequent programming visits may not be necessary. Additionally, Overstreet et al found that adults with lower stimulation levels performed better on speech perception tasks. Additionally, negative effects from high stimulation levels exist, including; risk of facial nerve stimulation, increased channel interaction, low battery life, voltage compliance issues and may result in an eventual degradation of the speech signal.

Frequently Asked Questions

What are the advantages of cochlear implants?

Cochlear implants provide deaf people with artificial hearing, allowing them to hear the world around them, and to communicate with others.
It makes their lives easier, and provides them with a sense of independence.
It also allows them to live ‘normal’ lives, and to participate in society

Do cochlear implants give 100% hearing?

Cochlear implants are the most common type of implant for deaf patients. This is a false statement. Cochlear implants help to replace the hearing loss, but cannot give 100% hearing.

What is the success rate of a cochlear implant?

The success rate of a cochlear implant is higher than that of a hearing aid. Cochlear implants help people with hearing loss to regain functional hearing. Cochlear implants provide a sense of hearing in people who are deaf.

What is the success rate of a cochlear implant?

Cochlear implants are successful if the patient has a severe-to-profound hearing loss as well. Although cochlear implant surgery is considered to be a safe and effective procedure, it’s not usually the first choice for a hearing loss. The surgery is expensive and needs to be done at a specialist centre.

Who is not eligible for a cochlear implant?
  1. People who have earwax (cerumen)
  2. People with a head injury
  3. People who have lost their hearing due to a serious medical condition
  4. People who cannot benefit from a cochlear implant due to genetic conditions.
  5. People who have other severe hearing conditions.
  6. People with severe or total deafness.
Do cochlear implants require brain surgery?

No, they do not require brain surgery. Cochlear implants can be inserted by a qualified otolaryngologist (ear doctor). A cochlear implant is a prosthetic device that is surgically implanted in the ear to restore auditory function to people who have severe to profound hearing loss.


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