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Cochlear Implants Enable People with Hearing Loss to be Social Again
NEW YORK (Sep 1, 2012)
We are surrounded by meaningful vibrations – music, the voices of family members and friends, the sounds of nature, and much more. We make sense of these vibrations through our hearing, a complex process that involves several parts of each ear including the cochlea, the snailshell-shaped organ at the end of the ear canal.
The cochlea contains thousands of cells that project minute "hairs," which pick up and translate those vibrations into electrical signals that the brain interprets as sound. One of the main causes of hearing loss in older people, is the loss or absence of these hair cells. "Many people with advanced hearing loss can benefit from a cochlear implant, a device that performs the same function as the ear: it picks up sounds via a microphone, processes them into electrical signals, and – bypassing the hair cells and other hearing structures – directly stimulates the auditory nerve, which carries these signals to the brain", said Kevin D. Brown, M.D., Ph.D., an Assistant Attending Otolaryngologist, who treats both adults and children with hearing loss at NewYork Presbyterian/Weill Cornell Medical Center.
Because communication is so fundamental to our well-being, cochlear implants are designed primarily to allow users to hear and understand speech, and for that reason implants have sophisticated speech recognition capabilities, said Dr. Brown. "Patients hear other sounds with a cochlear implant, but the processing strategies optimize the implant's ability to provide the patient with a perception of speech." This is more complicated than simply tuning to certain frequencies, he said. "The implant takes cues as far as timing and pitch, and sends the signals to different parts of the cochlea, depending on the frequency at which speech is occurring."
On average people with implants are able to understand about 80 percent of individual spoken words, but when those words are put together into full sentences with sentence and timing cues around each word, they get close to 100 percent of them correct.
Who Can Use Them?
As people age, many experience a progressive loss of hearing as the auditory hair cells die, and this can start happening to people in their 50s, their 70s, or not at all. The loss of hair cells first leads to a loss of the ability to perceive higher frequency sounds and often goes on to involve the lower frequencies, said Anil K. Lalwani, M.D., the Vice Chair of Research and Director of the Division of Otology, and Director of the Cochlear Implantation Program at NewYork Presbyterian/Columbia University Medical Center.
"One of the common complaints we get from people with high-frequency hearing loss is that sounds are not clear," said Dr. Lalwani. "Hearing aids, the first solution for mild or moderate hearing loss, are great for amplifying sounds but they don't necessarily restore the clarity of hearing." As hearing loss progresses hearing aids may no longer adequately help people understand speech clearly. "When their clarity is less than, say, 50 or 40 percent and people are frustrated that they can't talk on the phone or understand what people are saying, we start thinking about a cochlear implant," said Dr. Lalwani.
While about three quarters of cochlear implants are now done in older people, many older people who would benefit are just not aware of cochlear implants, said Dr. Lalwani, or they may be fearful of the anesthesia used during implant surgery. "But the consequences of not doing anything are huge," he added. Adults with significant hearing loss also lose their ability to communicate and typically start to withdraw socially, and may become depressed. "Cochlear implants can help people really blossom again and re-engage in social activities they enjoyed before their hearing loss," Dr. Brown added.
A small number of children are born deaf, and their lack of hearing may be picked up in hearing tests performed routinely on newborns. These children benefit greatly from cochlear implants. When implanted early, they are able to acquire speech and language much like hearing children and can attend regular schools. "The moment their implants are activated is like the day they were born as far as their hearing is concerned," Dr. Lalwani said. "They have to go through the process of learning to hear and acquire speech and language just like babies that hear normally."
One of the limitations of implants is their inability to translate the complex sounds of music. "Implants are not able to replicate the richness of the neural connections between hair cells and the cochlea and the neurons that transmit sound to the brain," Dr. Brown said. "We're getting better at it but we are not quite at the point where the majority of people are able to enjoy music with their cochlear implant." People with a history of musical training, whether they are professional or amateur musicians, tend to do better in their perception of music than people who have not had intensive music training in the past, Dr. Brown added.
Cochlear implant researchers are focusing on several areas. While it used to be common for people to get an implant in only one ear, bilateral cochlear implants are becoming more common, Dr. Lalwani said. Bilateral implants improve recipients' ability to localize sound. "We need two ears for sound localization just like we need two eyes for depth perception," he said. Two implants also help people understand what people are saying in a noisy background. In addition people with bilateral implants report that they're not as tired at the end of the day. "Imagine being at a noisy party and working hard to listen to a conversation. That's what it's like for hard of hearing person with a single cochlear implant. They have to focus, focus, focus," Dr. Lalwani said.
Another area of active investigation is the role of cochlear implants in people who have lost hearing in only one ear, said Dr. Lalwani. "In the past there was a concern that the brain would not be able to combine electrical hearing on one side with natural hearing on the other. It turns out that's just not true, and that brain is quite adaptable."
Research is also under way to find ways to avoid disturbing or destroying the hair cells that remain in people with hearing loss – and the remaining hearing in the ear. "Some patients still have some functional, particularly low frequency hearing," said Dr. Brown. "We have found that if we introduce the electrodes into the cochlea very carefully, we can preserve their low-frequency hearing, and they can hear both natural sound in the lower frequencies as well as the sound that is being brought in by the cochlear implant in the middle and higher frequencies."