Cochlear Implants

 

Cochlear implants are not a cure for hearing loss, but they can provide an opportunity to perceive sound. Research has shown that if parents are going to have their children undergo cochlear implant surgery, it’s best to do it sooner rather than later. Doing so can greatly improve the child’s speech and language development so that they are on target with their peer groups. While every surgery is serious and should not be considered lightly, it may reassure you to know that cochlear implant surgery has become routine. It may even be performed on an outpatient basis.

Cochlear Implant Surgery

Your child will be placed under general anesthesia. The entire procedure will typically no longer than two to three hours. Some hair may need to be shaved from the area. After sterilizing the skin, the surgeon will make an incision behind the ear. The surgeon will drill into the bone to create a “pocket” for the receiver. The surgeon will then drill through the mastoid bone to create access to the cochlea. He will insert the electrode array into the cochlea, and then close the incision with stitches.

Recovering from Surgery

After the surgery, your child will be taken to a recovery room until the effects of the anesthesia have worn off. When he wakes up, he might feel dizzy, pressure or discomfort in the ear, nauseous, or disoriented. He might have a sore throat from the breathing tube used during the operation.

It is likely that your child can return home the same day. Otherwise, he might need to stay overnight for observation. The doctor will provide a prescription for pain medicine, and he might also prescribe antibiotics as a preventative measure. A dressing might be placed over the ear, which may usually be removed the next day. The sutures will not need to be removed; they will naturally dissolve over time.

What is a cochlear implant?

A cochlear implant is an implanted electronic hearing device, designed to produce useful hearing sensations to a person with severe to profound nerve deafness by electrically stimulating nerves inside the inner ear.

These implants usually consist of 2 main components:

• The externally worn microphone, sound processor and transmitter system.
• The implanted receiver and electrode system, which contains the electronic circuits that receive signals from the external system and send electrical currents to the inner ear.

Currently made devices have a magnet that holds the external system in place next to the implanted internal system. The external system may be worn entirely behind the ear or its parts may be worn in a pocket, belt pouch, or harness.

What determines the success of cochlear implants?

Many things determine the success of implantation. Some of them are:

• How long the patient has been deaf--as a group, patients who have been deaf for a short time do better than those who have been deaf a long time
• How old they were when they became deaf--whether they were deaf before they could speak
• How old they were when they got the cochlear implant--younger patients, as a group, do better than older patients who have been deaf for a long time
• How long they have used the implant
• How quickly they learn
• How good and dedicated their learning support structure is
• The health and structure of their cochlea--number of nerve (spiral ganglion) cells that they have
• Implanting variables, such as the depth and type of implanted electrode and signal processing technique
• Intelligence and communicativeness of patient

How does a cochlear implant work?

A cochlear implant receives sound from the outside environment, processes it, and sends small electric currents near the auditory nerve. These electric currents activate the nerve, which then sends a signal to the brain. The brain learns to recognize this signal and the person experiences this as "hearing".

The cochlear implant somewhat simulates natural hearing, where sound creates an electric current that stimulates the auditory nerve. However, the result is not the same as normal hearing.

Why are there different kinds of implants?

Current thinking is that the inner ear responds to sound by at least two separate ways.

One theory, the place theory, says the cochlea responds greater to a simple tone at one place along its length. Another theory is that the ear responds to the timing of the sound.

Researchers, following the place theory, devised implants that separated the sound into groups. For example, they sent the lower pitches to the area of the cochlea where it seemed more responsive to lower pitches. And they sent higher pitches to the area more responsive to high pitches. Thus, they used several channels and electrodes spaced out inside the cochlea. Since there were also timing theories, researchers devised implants that made the sound signals into pulses to see if the cochlea would respond better to various kinds of pulses.

Most modern cochlear implants are versatile, in that they are somewhat capable of being adjusted to respond to sound in various ways. Audiologists try a variety of adjustments to see what works best with a particular patient.