Sound science: UI at the forefront of auditory advancements
Monday, October 28, 2013
In the late ’70s and early ’80s, as Sony Walkmans were revolutionizing the portable music-listening experience, another personal sound system transformation was just getting started. Scientists were experimenting with cochlear implants—devices that could translate sound into electronic signals, bypass faulty inner ear structures, and directly stimulate a patient’s auditory nerve. Such a system could conceivably deliver auditory information to a deaf person’s brain, allowing the person to perceive sound.
While many scientists and clinicians were skeptical, the idea excited Bruce Gantz, then a young otolaryngologist finishing up his residency at the University of Iowa.
Today, cochlear implants have become the standard of care for deaf individuals who want to perceive sound and interact with the hearing world. Modern implants restore “hearing” to adults who have become deaf and allow congenitally deaf children to learn to speak. More than 188,000 people worldwide now use these devices, including more than 41,000 adults and nearly 26,000 children in the United States.
Over the past three decades, Gantz and his colleagues at the Iowa Cochlear Implant Research Center have helped improve the success and expand the use of cochlear implants. They also helped develop a new cochlear implant, which combines electronic sound perception with a patient’s acoustic hearing, opening up implant technology to new patient populations and paving the way for patients to benefit from future advances in regenerative medicine.
A doctor’s career and a device develop together
Starting from those early days, Gantz’s career has dovetailed with the development of cochlear implants.
He worked with Bill House, a controversial leading proponent of the new technology, in Los Angeles in the late ’70s, where they implanted the first single-channel cochlear implant.
Subsequently, during a one-year surgical fellowship in Zurich, Gantz met and worked with many of the scientists leading the rapid development of implant technology in Europe, including Ingeborg and Erwin Hochmair in Vienna, who developed the Med El cochlear implant.
When Gantz returned to the UI in 1982, he arrived with four of the Hochmairs’ devices in his suitcase. Unlike the single-channel implants being tested in America at that time, the Hochmairs’ implant had four channels to deliver the electronic signal to the auditory nerve. Researchers thought that more channels would improve the performance of the implants.
“We were very excited, but the bottom line was they didn’t function any better than the single-channel implants,” Gantz says.
It took another international connection to provide the breakthrough Gantz was seeking. Researchers in Sydney, Australia, led by Graeme Clark, developed and implanted the first true multi-channel implant—dubbed the “bionic ear”—in 1978. Shortly before Christmas in 1982, Gantz visited Clark and his colleague, Dianne Meckelenburg, to learn about the device. He returned to Iowa with two of the multi-channel implants.
“We were the first U.S. site to put in the multi-channel Nucleus Cochlear Corp. device—we implanted two in one day—and lo and behold, they were spectacular compared to the single channel,” he says.
Iowa becomes Consumer Reports for implants
With success under his belt, Gantz set about building a research team and establishing a center that could systematically evaluate cochlear implants.
“I realized that all these different devices were being developed and they all had various claims for how well they worked, but no one was trying to figure out what was really working,” Gantz says. “We were not going to develop cochlear implants at Iowa—we didn’t have the engineering expertise at the time—but we could become the Consumer Reports of cochlear implants. We could test these devices uniformly.”
He tapped expertise from his own Department of Otolaryngology in the person of Richard Tyler, who developed the Iowa Cochlear Implant Test Battery. This series of standardized auditory tests, including the ability to hear in noise or quiet, as well as the ability to localize sound, allowed researchers to rigorously evaluate and compare the performance of different implants.
But Gantz knew that to be influential, the center needed to be truly multidisciplinary, so he also recruited experts from electrophysiology, speech pathology and audiology, and psychology. The group submitted its first grant application to the National Institutes of Health (NIH) in 1983.
“We were soundly rejected,” Gantz admits with a wry smile.
The grant reviewers, while not impressed with the initial proposal, recognized the importance of outcomes research for cochlear implants. When the UI team resubmitted its proposal in 1985, one year after the FDA first approved use of cochlear implants in adults, it was funded for five years with $2.6 million.
In 1988, the UI team published the first rigorous head-to-head comparison of single-channel versus multi-channel devices, demonstrating that multi-channel implants were indeed superior.
The Iowa Cochlear Implant Research Center has subsequently received five grant renewals from the NIH and is on course for 30 years of continuous funding in the amount of almost $50 million.
Since its inception, the center has made major contributions to cochlear implant technology. UI researchers, including Paul Abbas and Carolyn Brown, developed the neural response telemetry system, which measures residual auditory nerve activity and now is standard in all three FDA-approved implants. The system allows clinicians to “set” the implant for a recipient. It also provides a way to measure long-term effects of electrical stimulation on nerve function. Results from evaluating patients over several decades suggest that long-term stimulation helps maintain the neural environment.
Iowa researchers also pioneered the use of bilateral cochlear implants—implants in both ears—that can improve localization and hearing in noisy environments. And the UI was one of the first centers in the world to initiate systematic studies aimed at assessing and improving implant users’ music perception and enjoyment.
“Improved music perception can help normalize people’s lives, allowing them to enjoy the many things that music adds to our social and cultural fabric,” says Kate Gfeller, professor with joint appointments in the UI Department of Communication Sciences and Disorders and the UI School of Music. “Our work also has revealed very interesting overlaps between speech and music. We feel if the device can be improved for music perception, it may also have benefits for some of the more subtle aspects of speech, such as inflection and emotional tone.”
Gfeller and her colleagues were also the first to establish a “brain training” protocol that significantly improves aspects of music perception and enjoyment. For one patient, the protocol’s success came at her Christmas Eve church service.
“She told me that when the choir sang, ‘Do you hear what I hear?’ she understood it,” Gfeller says.
Preserving residual hearing leads to hybrid
By carefully tracking the progress of hundreds of patients over several decades, UI researchers have built a large, longitudinal database of patient outcomes. The database has helped define specific patient characteristics that predict cochlear implant success.
Early studies showed that duration of deafness is a key factor. The longer a person is deaf, the less successful a cochlear implant will be. Another emerging factor underlying successful patient outcomes is whether a person has any residual hearing.
Gantz recalls a teen who received a cochlear implant because his hearing aid was no longer helping him. With the implant, he could once again talk with his friends on the phone.
“He did spectacularly well combining the little bit of residual hearing with the electronic hearing provided by the implant,” Gantz says.
However, delivering electrical hearing to patients without eliminating residual hearing was not possible using a standard implant because the device destroys inner ear cells, and thus any residual hearing, in the implanted ear.
The UI team, including Christopher Turner, devised a remarkably simple solution: a shorter electrode that doesn’t reach as far into the cochlea as the standard implant, leaving the innermost portion of the cochlea unharmed. Gantz, Turner, and their colleagues developed the new “hybrid” implant with Cochlear Corp. The device, which combines acoustic and electrical hearing, was first implanted in 1999.
In comparison to the traditional implant, which replaces all hearing, the ability of the hybrid to preserve and use existing hearing offers important advantages to patients, including better understanding of speech in noisy environments, improved music appreciation, and the ability to localize where a sound is coming from.
Turner notes that successful use of the hybrid requires a highly skilled surgeon who can place the implant without interfering with the patient’s existing hearing.
But, because the hybrid doesn’t destroy residual hearing, it also can help new patient populations, including those with severe noise-induced hearing loss and high-frequency hearing loss due to aging. These patients previously had no solution to their problems; hearing aids didn’t work for them, and they had too much hearing to be considered for the traditional cochlear implants, which are only for deaf individuals.
“I am in phased retirement, and I cannot think of a more exciting finale to my career than to follow through on the acoustic-plus-electric hearing breakthrough that was developed here at Iowa,” Turner says. “I would love to see this idea become a widely accepted part of clinical practice.”
The importance of maintaining functional hearing in older adults was highlighted by a recent study from Johns Hopkins University showing that rates of dementia are much higher in people with significant hearing loss than in people of the same age who don’t have hearing loss.
Long-term use of the hybrid may also provide another benefit. In a decade-long study, the device appeared to stabilize patients’ hearing and prevent further decline, suggesting that implant stimulation actually helps preserve the auditory nerve.
This finding, coupled with the fact that the hybrid electrode spares inner ear cells and structures, suggests that hybrid implant recipients will be able to take advantage of potential future advances in regenerative medicine.
“Preservation of the inner ear is going to be important, because eventually we’ll be able to regenerate the nerves and even cells of the inner ear,” Gantz says.
As futuristic as it sounds, this idea is the subject of several research projects currently under way at Iowa. In one example, Marlan Hansen, assistant professor of otolaryngology, is collaborating with C. Allan Guymon, professor of chemical and biochemical engineering, to control nerve growth using micro-patterned polymer surfaces. If these surfaces can be used to direct growth of auditory nerve fibers, this approach might help improve the performance of cochlear implants.
“Regenerating the nerve in a way that increases the number of contacts between the nerve and the electrode of the cochlear implant would give a much better refined stimulation,” Hansen says. “You would get much closer to normal hearing.”
Across the UI, in three colleges and numerous departments, scientists and physicians continue to build on the institution’s tradition of cochlear implant expertise. Through cross-disciplinary collaboration, the team is improving cochlear implant performance, developing new devices, and laying the groundwork for a future where cellular, molecular, and genetic manipulation may ultimately allow researchers to cure or reverse deafness.
“Our ultimate objective is the translational process of trying to figure out how to improve hearing. It will take different concepts to make it happen, but that’s what makes this work so exciting,” Gantz says.
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