CochlearWords
-- Cochlear Implants Maintain Nerve Health in Deaf Cats --
Scientists from the Johns Hopkins University Center for Hearing and Balance have discovered why cochlear implants – devices intended to restore hearing –benefit some deaf children, but not others.
David Ryugo, P.h.D. and lead investigator of the study, used cochlear implants to electrically stimulate the nerves responsible for hearing in young, deaf cats. His results point to a link between introduced nerve activity, and the structure – abnormal or not – of the auditory nerve ending. Cochlear implants function to promote hearing, according to his study, because they preserve normal structure at the end of the auditory nerve.
Deaf humans probably benefit from implants in the same way that Ryugo’s cats did. Both species have similar auditory systems, and “the cochlear implants used in these cats are the same technology that was developed for deaf children,” he said. ”but smaller.”
Until now, scientists have not understood how cochlear implants work. “It has just been assumed that the auditory system functions normally when an implant is inserted,” Ryugo explained. “The reasoning has been something like this: if a car runs out of gas, it stops. Put gas in, and the car runs again.” Ryugo’s work is filling in the gaps, though, illustrating exactly how the “gas” – or cochlear implants – jumpstart the hearing process in congenitally deaf children.
Each year, 3 out of 1000 children in the United States are born unable to hear. Not every parent of a deaf child considers cochlear implantation, but for those who do, understanding the trade-off between waiting and acting is important. The success of implantation, according to Ryugo’s study, depends upon how far nerve ending abnormalites can advance. If children born deaf are left untreated for too long, their nerve endings start to wither. Eventually, this withering abnormality may become irreversible; implants can’t restore the nerve.
“Younger is clearly better, as far as treatment with cochlear implants goes,” explained Ryugo. “In Europe, they’re even putting implants in kids at 12 months,” Ryugo said, “but it is always difficult to know the age at which a child is strong enough to endure the surgical process, and to know how much leeway doctors have when deciding how long they can wait to perform surgery.” Ryugo’s work will help define the “window of opportunity” for cochlear implantation though, by illustrating how these devices impact physical abnormalities in the nerve ending of a deaf ear.
In his study, published in Science on December 2nd, young deaf cats with implants responded to sounds in their environment. “They exhibited certain behavior responses that alerted us to the fact that they were hearing,” Ryugo said. He had trained each implanted cat that a particular sound -- a rhythmic cadence, finger-snapping, or hand clap, for example -- signaled a special food treat. Different sounds signaled different treats (tuna, roast beef, sardines) to the different cats, he explained, “and voila! They would come to these sounds the same way a hearing cat comes when you shake its food box. We knew they could hear.”
Ryugo’s graduate student Erika Kretzmer compared nerve tissue from the inner ears of three groups: deaf cats with implants, deaf cats without them, and normal hearing cats. She discovered that deaf cats that had received cochlear implant stimulation actually maintained the nerve connections critical to hearing.
“There wasn’t a significant difference between nerve endings of normal hearing cats and implanted cats,” Ryugo said.
In the deaf cats without implants, however, nerve connections were withered. “Their nerve endings were disrupted,” explained Ryugo. “They were stubby and truncated, like trees growing on the edge of a windy cliff.”
Nerve endings promote communication between neurons in the auditory pathway. They exhibit structural characteristics which advance the release and capture of chemicals called neurotransmitters. This process permits sound to reach the brain. It permits hearing.
Until now, there’s never been a good group of animal models to use for studying the effects of cochlear implants in the deaf. “We’re the only ones in the country with a colony of congenitally deaf cats,” Ryugo explained. The cochlear implants were unique, too; Advanced Bionics specially miniaturized the implants just for his study.
Cochlear implants work by performing an essential step in the hearing process: they convert sound vibrations into electrical impulses that hit the auditory nerve, and then travel to the brain. A deaf child has inner ear damage that prevents him from generating these electrical signals, however. So the cochlear implant does it for him. Ryugo’s research suggests that implants are only capable of preserving auditory nerve structure if inserted in a timely fashion, before the nerve ending withers away.
In the future, Ryugo wants to further define the “window of opportunity” for cochlear implantation by performing time-course studies to elucidate exactly how nerve endings in the ear develop.
The researchers were funded by The Emma Liepmann Endowment Fund, and grants from the NIH and the Advanced Bionics Corporation. Authors on the paper are David Ryuogo, Erika Kretzmer, his graduate student, and John Niparko, all at Johns Hopkins School of Medicine.
.MGW.
Scientists from the Johns Hopkins University Center for Hearing and Balance have discovered why cochlear implants – devices intended to restore hearing –benefit some deaf children, but not others.
David Ryugo, P.h.D. and lead investigator of the study, used cochlear implants to electrically stimulate the nerves responsible for hearing in young, deaf cats. His results point to a link between introduced nerve activity, and the structure – abnormal or not – of the auditory nerve ending. Cochlear implants function to promote hearing, according to his study, because they preserve normal structure at the end of the auditory nerve.
Deaf humans probably benefit from implants in the same way that Ryugo’s cats did. Both species have similar auditory systems, and “the cochlear implants used in these cats are the same technology that was developed for deaf children,” he said. ”but smaller.”
Until now, scientists have not understood how cochlear implants work. “It has just been assumed that the auditory system functions normally when an implant is inserted,” Ryugo explained. “The reasoning has been something like this: if a car runs out of gas, it stops. Put gas in, and the car runs again.” Ryugo’s work is filling in the gaps, though, illustrating exactly how the “gas” – or cochlear implants – jumpstart the hearing process in congenitally deaf children.
Each year, 3 out of 1000 children in the United States are born unable to hear. Not every parent of a deaf child considers cochlear implantation, but for those who do, understanding the trade-off between waiting and acting is important. The success of implantation, according to Ryugo’s study, depends upon how far nerve ending abnormalites can advance. If children born deaf are left untreated for too long, their nerve endings start to wither. Eventually, this withering abnormality may become irreversible; implants can’t restore the nerve.
“Younger is clearly better, as far as treatment with cochlear implants goes,” explained Ryugo. “In Europe, they’re even putting implants in kids at 12 months,” Ryugo said, “but it is always difficult to know the age at which a child is strong enough to endure the surgical process, and to know how much leeway doctors have when deciding how long they can wait to perform surgery.” Ryugo’s work will help define the “window of opportunity” for cochlear implantation though, by illustrating how these devices impact physical abnormalities in the nerve ending of a deaf ear.
In his study, published in Science on December 2nd, young deaf cats with implants responded to sounds in their environment. “They exhibited certain behavior responses that alerted us to the fact that they were hearing,” Ryugo said. He had trained each implanted cat that a particular sound -- a rhythmic cadence, finger-snapping, or hand clap, for example -- signaled a special food treat. Different sounds signaled different treats (tuna, roast beef, sardines) to the different cats, he explained, “and voila! They would come to these sounds the same way a hearing cat comes when you shake its food box. We knew they could hear.”
Ryugo’s graduate student Erika Kretzmer compared nerve tissue from the inner ears of three groups: deaf cats with implants, deaf cats without them, and normal hearing cats. She discovered that deaf cats that had received cochlear implant stimulation actually maintained the nerve connections critical to hearing.
“There wasn’t a significant difference between nerve endings of normal hearing cats and implanted cats,” Ryugo said.
In the deaf cats without implants, however, nerve connections were withered. “Their nerve endings were disrupted,” explained Ryugo. “They were stubby and truncated, like trees growing on the edge of a windy cliff.”
Nerve endings promote communication between neurons in the auditory pathway. They exhibit structural characteristics which advance the release and capture of chemicals called neurotransmitters. This process permits sound to reach the brain. It permits hearing.
Until now, there’s never been a good group of animal models to use for studying the effects of cochlear implants in the deaf. “We’re the only ones in the country with a colony of congenitally deaf cats,” Ryugo explained. The cochlear implants were unique, too; Advanced Bionics specially miniaturized the implants just for his study.
Cochlear implants work by performing an essential step in the hearing process: they convert sound vibrations into electrical impulses that hit the auditory nerve, and then travel to the brain. A deaf child has inner ear damage that prevents him from generating these electrical signals, however. So the cochlear implant does it for him. Ryugo’s research suggests that implants are only capable of preserving auditory nerve structure if inserted in a timely fashion, before the nerve ending withers away.
In the future, Ryugo wants to further define the “window of opportunity” for cochlear implantation by performing time-course studies to elucidate exactly how nerve endings in the ear develop.
The researchers were funded by The Emma Liepmann Endowment Fund, and grants from the NIH and the Advanced Bionics Corporation. Authors on the paper are David Ryuogo, Erika Kretzmer, his graduate student, and John Niparko, all at Johns Hopkins School of Medicine.
.MGW.
posted by Meagan G at
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