Knowing how a cochlear implant works may help kids better understand their new bionic ear and the cool technology behind it that allows them to hear better.
Here's how the implant works:
- The microphone picks up sound.
- Sound is sent to the sound and speech processor.
- The processor analyzes the sound and converts it into an electrical signal. (The signal contains information that determines how much electrical current will be sent to the electrodes.)
- The transmitter sends the signal to the implant package, where it's decoded.
- The implant package determines how much electric current should pass to the electrodes and sends the signal. The amount of electric current determines loudness, and the position of the electrodes determines the sound's pitch.
- The nerve endings in the cochlea are stimulated and the message is sent to the brain along the auditory nerve.
- The brain interprets the sound and the person hears.
Cochlear Implant Surgery
Surgery for a cochlear implant takes 2–4 hours and uses general anesthesia (which keeps a patient completely unconscious). The surgeon will place and secure the implant package under the skin and inside the skull, then thread the wires containing the electrodes into the spirals of the cochlea.
To secure the implant, the surgeon first drills a 3- to 4-millimeter bed in the temporal bone (the skull bone that contains part of the ear canal, the middle ear, and the inner ear). Then, the surgeon opens up the bone behind the ear to allow access to the middle ear. A small hole is drilled in the cochlea and the wires containing the electrodes are inserted. The implant package is then secured and the incision is closed with stitches.
After cochlear implant surgery, a child:
- will probably be able to go home the next day
- will have to wear a dressing over the implant area for 24 hours
- might be off-balance or dizzy for a few days
- may have mild to moderate pain (the doctor may recommend giving pain medicines)
- won't have to have the stitches removed (they're absorbable and dissolve on their own)
- can lie on the side of the cochlear implant in a few days
About 2 to 4 weeks after surgery, the sound and speech processor is matched with the implant package and is programmed and fine-tuned to meet the child's individual hearing needs.
Nowadays, children who are born deaf or with a profound hearing loss in both ears can even receive two cochlear implants, one for each ear, at the same time. This is a great advance as it requires only one surgery.
Learning to Use a Cochlear Implant
Because the hair cell damage, electrical signal patterns, and sensitivity of the auditory nerve are different for each person, a specialist must fine-tune the sound and speech processor for every patient.
By measuring the lowest and highest current for each electrode, the clinician finds the softest and loudest sounds that will be heard (each electrode produces a different sound with different pitch). The sound and speech processor matches sounds on different electrodes with different volumes and attempts to create an accurate version of the original sound. However, because a limited number of electrodes are taking over the function of the thousands of hair cells in a normal ear, sounds won't be totally "natural." However, infants who never heard before will be able to make great sense of these sounds and will quickly learn language.
After the first few programming sessions, the user begins to pick up sounds with the implant, but giving the implant full power is a gradual process that takes several months. In children who are born deaf, the stimulation from the implant will allow them to develop the brain pathways necessary to hear sounds and develop speech and language. This is an extended process with programming and intensive therapy that often lasts for several years.
During the programming process, the user attends speech and language therapy sessions to help identify and interpret the new sounds he or she is hearing. An important part of the therapy is parent education and training.
Therapy will help a child develop and understand spoken language through detecting, imitating, and associating meanings of sounds. These sessions last at least a year, along with parent education and training programs. In many cases, therapy has helped kids with cochlear implants develop speech and language on par with their peers.
Some families choose to have implants in both ears. This can help with speech detection when there is background noise.
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