Cochlear implants have been around for years, restoring hearing for many people. But, as this ScienCentral video explains, a new version promises to improve the quality of what patients hear.
Dr. David Acus of Herrick Memorial Hospital in Tecumseh, Michigan was a twenty-five year veteran of the emergency room when hearing loss forced him to quit his job. Then he got a cochlear implant.
“The cochlear implant is wonderful. It’s allowed me to go back to work.”
In a healthy ear, vibrations are translated into electrical signals inside the cochlea, a small bony structure of the inner ear. The signals are sent to the brain via the auditory nerve. Congenital problems, injury, illness, or aging can cause hearing loss. One solution is to insert an electrical array into the cochlea that translates external sounds into electrical impulses.
These conventional cochlear implants are remarkably effective, and have improved the hearing of nearly 100,000 deaf people worldwide. However, the implants stimulate the ear's auditory nerve indirectly, through the bony wall of the cochlea. Neuroscientist John Middlebrooks of the University of Michigan points out that muddles music and vocal tones.
“It’s a little bit like playing a piano with boxing gloves on your hands: you can make a big sound, and you can touch all the keys, but you can’t play single keys individually.”
Conventional cochlear implant. Middlebrooks points to auditory nerve.
Middlebrooks and his colleague Russell Snyder at the University of California, San Francisco have developed what they believe is a better solution–a tiny silicon device designed to be implanted directly in the auditory nerve.
They published their findings in the Journal of the Association for Research in Otolaryngology. To test the efficacy of the new device, they used three animal models: normal hearing, a conventional cochlear implant, and a new intra-neural implant. They played a tone and looked at the response of the auditory midbrain, a portion of the brain that interprets sounds.
Brain's response to hearing a tone. Coutesy John Middlebrooks.
In normal hearing, there is a strong response corresponding to frequency played. With the conventional cochlear implant, the brain registered sound, but not at a specific frequency. With the new intra-neural implant, the graph shows a strong, specific response–similar to normal hearing.
Middlebrooks explains the benefits of the new device. “It will give people hopefully better hearing in complex environments and also some perception of pitches, so they’ll be able to enjoy music and also understand the melodious quality of other people’s voices.”
Conventional cochlear implant external microphone and battery pack.
He adds the implant has another advantage. It’s so small and uses so little electricity, it may be possible to implant the entire device under the skin. That means people could wear them in the shower or while swimming, giving them 24-hour-a-day hearing with no external battery to charge.
Researchers need to verify the safety of the new implants. And they hope to start human trials in about five years. In the meantime, Middlebrooks encourages people to go ahead and get a cochlear implant now if they are a good candidate for one. Doctors should still be able to implant an intra-neural device at a later time when it becomes available.
Publications: JARO. January 30, 2007.
Research funded by: National Institute on Deafness and Other Communication Disorders.
