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Cochlear Implants

  • A cochlear implant is an electronic device to provide a sensation of hearing to individuals who are deaf. It consists of two main parts: an external part worn somewhat like a hearing aid, and an internal part which must be implanted by a surgeon.

    How Boston Children's Hospital approaches cochlear implants

    The Cochlear Implant Program at Boston Children's Hospital is an interdisciplinary program within the Department of Otolaryngology and Communication Enhancement.

    • It provides a unique opportunity for children who are deaf and for their families.
    • The program, led by Greg Licameli, MD, is the largest and most comprehensive pediatric cochlear implant program in New England.
    • We offer advanced technology combined with unparalleled personal care, provided by a team of highly qualified clinicians.

    Boston Children's Hospital
    300 Longwood Ave
    Boston MA 02115
     fax: 781-216-2252

  • In-Depth

    How is a cochlear implant put together?

    The external part of a cochlear implant is the speech processor. It has a "microphone" worn over or behind the ear. A cord leads from the microphone to the speech processor. The speech processor codes the sound input into electrical signals which are sent back to the "transmitter," a thin plastic piece about one inch in diameter containing a magnet placed on the side of the head behind and slightly above the ear.

    In turn, the transmitter sends the signals across the skin to the internal part of the implant (the "receiver/stimulator"), which is under the skin. The receiver/stimulator sends the signals into the electrode array, which is a one-inch long wire surgically inserted into the inner ear. The electrode array consists of an array of electrode bands, each of which can provide a tiny current to the inner ear, to replace the function of the damaged or missing hair cells which ordinarily would stimulate the nerve endings of the auditory nerve.

    Will a cochlear implant provide normal hearing?

    A cochlear implant provides a limited sense of hearing. However, a cochlear implant combined with visual cues usually let most people understand spoken language.

    Who can benefit from a cochlear implant?

    Adults and children who used to have normal hearing or partial hearing—who learned to talk before they became deaf—often benefit from a cochlear implant.

    If your child was born deaf or became deaf before he or she learned to talk, cochlear implants can also help. It just might take longer for them to understand spoken language.

    What range of hearing loss must my child have to benefit from an implant?

    To be a candidate for a cochlear implant, your child must have a severe or profound sensorineural hearing loss in both ears.

    The average hearing level in the speech frequency range (500-2000Hz) must be poorer than 70 decibels in both ears without hearing aids, and with hearing aids your child must not be able to recognize single words clearly out of context without looking at the talker's face.

    If your child is younger than 2, her hearing loss must be 90 decibels or greater in both ears.

    At what age should my child receive a cochlear implant?

    The Food and Drug Administration allows cochlear implants for children beginning at age 12 months. A congenitally deaf child who is going to have a cochlear implant should have the surgery before the age of four years, earlier if possible. This early implantation gives your child the best chance to learn to use sound while language skills are developing.

    Children who once had normal hearing or partial hearing, and then became deaf, may be implanted as soon as it is clear that there's no benefit from a hearing aid.

    What factors might favor or limit my child's benefit from a cochlear implant?

    Ask yourself and your physician:

    • Does my child have good cochlear anatomy?
    • Does my child have good underlying language abilities?
    • Did she have a solid base of language development prior to surgery?
    • Will we participate in regular speech/language therapy given by a cochlear-trained clinician?
  • How is cochlear implant surgery performed?

    Implant surgery is performed under general anesthesia and takes three to six hours. Your child stays in the hospital one or two nights after the surgery. This can be a traumatic time, and you are encouraged to stay in your child's room during surgery and recovery.

    During the surgery, the receiver/stimulator and electrode array are implanted.

    An incision is made behind the ear for the surgeon to expose the area of the round window, a tiny membrane at the separation between the middle ear and the inner ear.

    Then the surgeon places the receiver/stimulator in a small area on the side of the head where the bone has been drilled thinner to make a place for the receiver/stimulator to fit—outside the skull but under the skin. Your child's brain is not exposed or penetrated during the surgery.

    The electrode array is inserted into your child's inner ear, and the receiver/stimulator is fixed in place over the bone. Electrical recordings are made to show that the electrodes are providing stimulation.

    The skin is then surgically closed over the implant.

    What are the risks of cochlear implant surgery?

    The risks of anesthesia are the same as for any surgery. Surgery to the inner ear also carries the risks (although uncommon) of facial nerve paralysis, loss of taste sensation, dizziness, or ringing in the ear. The surgery does destroy any ability the individual may have had to hear with a conventional hearing aid in that ear. Bear in mind that at some point, your child may need a replacement implant.

  • Research & Innovation

    Most cases of deafness are caused by the dysfunction or death of cells in the cochlea, the snail-shell-shaped structure in the inner ear. Douglas Cotanche, PhD, a researcher in Otolaryngology, now reports that his lab has grown all the assorted cell types in the cochlea from just one source: neural stem cells. The study was published online June 20 by the journal Hearing Research.

    Neural stem cells were first isolated from mice in 1998 by Evan Snyder, MD, PhD, formerly of Children's Department of Neurology. Cotanche's team implanted the cells deep inside the sound-damaged cochleas of guinea pigs and mice. Six weeks later, the cells had migrated throughout the cochlea and formed satellite cells, spiral ganglion cells and Schwann cells, which make up the cochlea's nervous tissue, as well as the hair cells and supporting cells of the organ of Corti (the actual hearing organ). "Getting these cells to integrate into the damaged ear and make the variety of cochlear cell types is a big step," says Cotanche.

    The researchers couldn't show complete rebuilding of the cochlea, but they believe that with more time and more stem cells, most of the cochlea could be repopulated. Cotanche's next goal is to implant human neural stem cells in animals and test whether the new cochlear cells connect with the auditory nerve and the brain, and whether they respond to sound stimulation—in other words, whether they restore hearing.

  • Your Story

    Breaking the silence

    Cochlear Implants While sitting across from each other at the kitchen table, Heidi Harrington asked her daughter, Hannah, "Where's Yoda?," to which the 6-year-old casually replied, "He's dead." In most situations, acknowledging the passing of a family hamster would have been sad, but Heidi and her husband, Jack, started crying tears of happiness. Their conversation took place shortly after Hannah's first "mapping" session to activate her new cochlear implant, and Heidi was testing how well Hannah could hear. "She understood us and answered perfectly—it was just unbelievable," says Heidi.

    Hannah inherited Waardenburg syndrome, a condition that can cause mostly benign symptoms, like a white streak of hair, differently colored eyes or webbed toes. But Hannah suffered the most serious symptom—hearing loss. She had hearing problems from birth, so learned to communicate via sign language and could understand some speech with the help of powerful hearing aids. But the textured, layered world of hearing was lost to her, and over the years, her hearing worsened. Last year, it became clear she wasn't hearing at all, and her grasp of language started to slip away.

    This turn of events had a silver lining for the Harringtons, since it meant that Hannah now qualified for a cochlear implant, a device that's been restoring the hearing of people who are deaf for nearly two decades. Hannah hadn't been "deaf enough" to be a candidate before she turned 6. Since the surgery to place a cochlear implant is major and cuts off the patient's residual ability to hear, it's only performed when hearing aids don't help at all.

    By the time Hannah qualified, she was older than the ideal implant candidate. "Hearing is a 'use it or lose it' phenomenon," says Hannah's surgeon, Greg Licameli, MD, director of the Cochlear Implant Team at Boston Children's Hospital. Research shows that children who receive implants when they are as young as 1 make greater strides in their language abilities than older children. But Hannah was still eligible, since she'd developed some language skills before losing her hearing and was therefore more likely to regain them. She also passed the implant team's rigorous evaluation process, in which audiologists, speech pathologists, psychologists, developmental pediatricians and surgeons all weigh in on a candidate's likelihood of success. "If Hannah never had hearing and didn't have good access to rehabilitation post-surgery, we wouldn't have been optimistic and probably wouldn't have done the surgery," says Licameli.


    Cochlear implants have two parts: an external microphone, sound processor and transmitter system, and the receiver and electrode system that gets implanted in the head behind the ear. Whereas hearing aids amplify sounds, implants stimulate the hearing nerve directly by receiving sound from the outside environment, converting it into digitized signals and transmitting those signals to the electrodes in the cochlea, the spiraled cavity of the inner ear. While the brain learns to recognize the signals as sounds, the patient doesn't experience it as hearing, per se, especially not at first.

    "Many people say it feels more like a pressure or a sensation," says Lynne O'Brien, Hannah's audiologist. "Then it turns into a squawking noise that some kids say sounds like chickens. At first, everything sounds like one big barnyard."

    After Hannah's surgery, when she had devices implanted behind and in her right ear, she came back to Children's to get them turned on. This happens in several stages, during which O'Brien gradually exposes Hannah to sounds and maps her processor to pick up softer and more wide-ranging noises. The first session can be incredible for the patient, her family and the clinicians. "It's amazing to see that moment when it's activated, especially with kids who've never even heard a beep before," says O'Brien. "Children point to their ear and their faces light up with surprise."

    Sometimes, when the microphone gets switched on, all the people in the room—especially the parents—start crying when they see the child's expression when they hear. "We have to be careful because that can be scary for the child, since the very first thing she hears is the sound of everyone sobbing."

    Over the years, doctors have taken this into account and adjusted the turning-on process. "As technology improves, we have the capability of turning it on bit by bit so kids aren't as overwhelmed," O'Brien says. Still, hearing for the first time—or hearing in a whole new way—can be a shock. "The ride home is strange for lots of kids, as they hear the wheels on the pavement, the wind against the windows, the radio, people eating and talking all at once," says O'Brien. "They suddenly have a whole new sense and it's so strange for them, with all this sound coming in and them not being able to make sense of it yet."

    The turning-on, or mapping process, is painstaking, as audiologists carefully test patients' hearing range and adjust the transmitter for two-hour sessions, every few months. One time, a patient of O'Brien's came running back after a session, upset that the device was defective and making thumping noises. "It turned out it was his footsteps that he was hearing for the first time," she says. "Sounds can drive people nuts until they can identify them and learn to put them in the background."

    Ever since the day Heidi first tested Hannah's implant (Hannah said through sign that the squawking sounded like monkeys), her parents haven't been able to stop trying out her new abilities. "It's just fascinating to watch her discover the hearing world," says Heidi. When Hannah had Rice Krispies for breakfast a few months ago, she erupted in shouts of 'Pop! Pop!,' simply amazed that her that cereal bowl was making noise. So far, she's been through four mapping sessions, and each time she lights up in delight when she hears sounds she didn't know existed. In her most recent session, she heard high-frequency sounds like "f" and "sh" for the first time. "The subtleties of language are coming to her now," says Heidi. "Every week, we're seeing something different. She can tell you the difference between a plane, helicopter and blimp without seeing them. She's so excited about hearing and is really having fun."

    Right now, Hannah can't localize sound well, so she still searches for where sounds come from. This brings with it its own amusements: Recently she was looking down at a pool of water to watch fish swimming while noisy black birds flew overhead. "She heard the 'caw!' while staring at the fish and we could see her trying to mentally process—'Do fish make that noise?'" says Heidi.


    Cochlear implants used to be a highly contentious topic among members of the deaf community, as many took offense at the idea that restoring hearing is "correcting" something they don't see as a disability. But according to Licameli, the controversy has waned over time, as the benefits of implants have become evident. "We've been able to demonstrate that it really does work," he says. "Now we have deaf parents come to us with their deaf child to explore implants for the child. Ten years ago, that never would have happened."

    For Jack and Heidi, the decision was clear-cut. "Hannah was missing so much, we needed to go to the next step," Jack says. Hannah is among the 98 percent of deaf children who have hearing parents; while the Harringtons all used sign language, the fact that she can talk to her brother, Jake, and to her parents, has changed the family dynamic drastically. "Hannah's always been social, but now she constantly has something to say and loves telling us stories," says Heidi. "There was a day last week when I said, 'Child! Can you just be quiet for a minute?' and I couldn't believe what I said. For years, she wasn't talking at all. Her ability to participate in the world has dramatically improved because people can understand her and she can understand them."

    Looking ahead, Hannah is a good candidate for a cochlear implant on her left ear and will be evaluated this winter. Generally, the second implant happens a year after the first, to give patients time to adjust. The second one would give her a better ability to differentiate sounds in noisy situations and the ability to hear in stereo, which helps in localizing noises. "We can't wait to get the other side done, if the first is any indication," says Jack. "Her speech clarity has improved beyond what we could have imagined, and she's telling us in every way that she wants it." In the meantime, Hannah is taking advantage of modern technology. Her device comes with an iPod input, and she can't get enough of the song "Who Let the Dogs Out?" by the Baha Men. "She loves music and glows when we play it," says Jack. "It's one of her favorite things."

    "We do a lot of things in medicine that affect the quality of life, but this is life-changing," says Licameli. "That's the reason I enjoy it. I'm lucky to do it."

    Heidi feels lucky too. "When I was a kid, the scariest thing was the thought of going blind or deaf," she says. "But deaf people have options now. There are so few true miracles in this world. This is one of them."

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