Penetrating the Secrets of the Cochlear Nucleus Emerging implant technologies on the horizon hold promise for audiologists and consumers with Neurofibromatosis Type II (NF2) in providing better pitch resolution and speech understanding. More than 245 people with NF2 have received auditory brainstem implants (ABIs), which were approved in 2000 by the U.S. Food and Drug Administration (FDA). ... Features
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Features  |   December 01, 2002
Penetrating the Secrets of the Cochlear Nucleus
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Hearing Disorders / Hearing Aids, Cochlear Implants & Assistive Technology / Audiologic / Aural Rehabilitation / Balance & Balance Disorders / Special Populations / Genetic & Congenital Disorders / Research Issues, Methods & Evidence-Based Practice / Regulatory, Legislative & Advocacy / Language Disorders / Features
Features   |   December 01, 2002
Penetrating the Secrets of the Cochlear Nucleus
The ASHA Leader, December 2002, Vol. 7, 1-16. doi:10.1044/leader.FTR2.07122002.1
The ASHA Leader, December 2002, Vol. 7, 1-16. doi:10.1044/leader.FTR2.07122002.1
Emerging implant technologies on the horizon hold promise for audiologists and consumers with Neurofibromatosis Type II (NF2) in providing better pitch resolution and speech understanding.
More than 245 people with NF2 have received auditory brainstem implants (ABIs), which were approved in 2000 by the U.S. Food and Drug Administration (FDA). Cochlear implants are not an option for patients with NF2, a genetic disease that produces benign tumors on both auditory nerves, which are severed when the tumors are removed. An ABI transmits sound through electrical impulses to an array with 21 electrodes implanted on the surface of the cochlear nucleus in the auditory brainstem. Although multiple electrodes are used, performance usually has been equivalent to stimulation with a single channel.
“Although we had hoped that the current ABI would allow multiple-channel information, patients don’t seem to be using the various channels. One possibility is that the channels blend together electrically,” said Robert Shannon, who directs the auditory research laboratory at the House Ear Institute (HEI) in Los Angeles.
The results with the ABI are similar to performance with the early, single-channel cochlear implants, noted Terry Hambrecht, special consultant to the National Institute on Deafness and Other Communication Disorders (NIDCD) for auditory prostheses. “Patients cannot take advantage of all of the frequencies presented—very few can tell them apart,” he said.
Next Generation Implant
To make the ABI more effective, Hambrecht said, the device must penetrate the auditory nucleus to take advantage of its tonotopic organization. After 12 years of basic research, a penetrating ABI has been developed with six needle-like electrodes. “The electrodes are arranged at different lengths to stimulate different frequency regions within the cochlear nucleus, with the hope of providing better pitch perception,” he said.
The FDA approved a Phase I clinical trial for the penetrating ABI, and the first candidate is expected to undergo surgery within a year. The implant was developed as the result of collaboration between the HEI, Huntington Medical Research Institutes, and Cochlear Americas, with funding from the NIDCD and FDA.
The penetrating ABI device used in the trial will have electrodes that contain both the surface array used in the current device and the penetrating array. “This allows us to test each array separately so that we can see the advantages of this type of stimulation,” said Steve Otto, clinical coordinator of the ABI project at HEI.
Audiologist’s Role
The role of the audiologist in working with patients with NF2 is critical and multifaceted, Otto said. Audiologists need to be supportive and encouraging, as well as being experienced clinicians and adept at electronics. “Patients with NF2 have a serious disease and ask a lot of questions about the disease and the ABI,” he said.
“The audiologist needs to tell the patient what the ABI can and cannot do, and ensure that the patient’s expectations are reasonable,” Otto added. “Audiologists must also review this with the patient before the initial stimulation.”
The ABI provides access to environmental sounds and supplements speechreading, but few patients can understand speech using audition only, he noted. Using ABI sound in combination with speechreading, most patients score about 65% on tests of sentence recognition, an increase of about 30% compared with speechreading alone. After two years of ABI use, some patients can understand 20% on CUNY sentences without speechreading. In contrast, more than 50% of those with current cochlear implant devices can understand speech without speechreading.
Programming an ABI is similar to programming a cochlear implant, except that some patients may not perceive any pitch differential, and a greater number of patients experience non-auditory sensations, Otto noted.
“With the penetrating ABI that will be in clinical trials, we will have the ability to stimulate more discrete populations of neurons in the higher auditory centers,” he said. The programming process often can require extra time to explore other modes of stimulation available through the programming system to eliminate any minor tingling or other non-auditory sensations that can occur.
With the success of the penetrating ABI, Otto believes that the implant could find more applications in other patient populations. ABIs have already been implanted in individuals who have had cochlear ossification after meningitis as well as cochlear malformation.
“It’s important for audiologists and speech-language pathologists to be aware that there is help for patients with NF2 or other conditions that affect the auditory nerve,” Otto said.
For more information about ABIs, contact the House Ear Institute at 213-483-4431 or visit http://www.hei.org/.
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December 2002
Volume 7, Issue 12