Next-generation cochlear implants aiming for hearing loss from aging

From: Canada.com - Hamilton,Ontario,Canada - Mar 14, 2006

Provided by: Canadian Press
Written by: LAURAN NEERGAARD
Mar. 14, 2006

WASHINGTON (AP) - Cochlear implants may not be just for the profoundly deaf anymore: Iowa scientists are developing the next generation, a "hybrid implant" to combine the best of bionics with regular hearing aids for age-related hearing loss.

If it works it one day may help thousands whose hearing progressively fades as they age. Unlike regular cochlear implants, the hybrid model would let people keep their natural music appreciation even as it helps them hear speech more clearly again.

That's what attracted attorney Gordon Gross, a concert lover, to the experimental device five months ago. With his hearing aids at full blast, Gross could conduct one-on-one conversations. But he could barely distinguish sentences from the background noise during the meetings required for his job.

"Most people in my situation smile a lot, fake what they hear," says Gross, 74, of Buffalo, N.Y.

He's still undergoing required training to learn to recognize speech with the implant. But Gross recently popped in a Phantom of the Opera CD and noticed that, "where before I wouldn't understand virtually anything, I'm now beginning to pick up words and phrases. It is very exciting."

How does it work? Like tuning a piano, says Dr. Bruce Gantz, an otolaryngologist at the University of Iowa who invented the hybrid model now being tested at 26 medical centres around the country.

Normally, microscopic hair cells in the cochlea, the snail-shaped inner ear, pick up vibrations and convert them into electrical impulses that the brain recognizes as different sounds. Hairs in the deepest part of the cochlea pick up low-frequency sounds, such as music. Hairs at the cochlea's entrance pick up high-frequency sounds, including speech.

With age-related hearing loss, people tend to first lose high-frequency hearing. Initially, specific consonants disappear - they no longer can discriminate, say, a "c" from a "t." They stumble over more and more words until they're unable to decipher entire sentences, especially when there's competing noise. Hearing aids turn up the volume for all sounds, not just speech, and thus eventually quit helping.

"If you filter those (consonants) out to a great extent, you can make the sound as loud as you like and it's still incomprehensible," explains Dr. James Battey, who directs the National Institutes of Health's hearing-loss division.

Enter cochlear implants. Surgically placed behind and in the ear, the implant itself turns sound into electrical impulses that directly activate the hearing nerve, allowing the deaf to hear. They've proven particularly beneficial for deaf babies and young children, dramatically improving their ability to learn to speak and comprehend language normally.

But for people who aren't completely deaf, cochlear implants have a big catch: snaking the electrode deep into the cochlea destroys whatever hair cells still live in the inner ear. If your only problem is detecting high-frequency sounds, a regular cochlear implant would destroy your ability to hear low-frequency sounds normally, such as music or the pitch that distinguishes one speaker from another.

Gantz's solution: Make the electrode shorter, so it only substitutes for the hearing that's already lost. Pair it with a regular hearing aid to amplify their remaining low-frequency hearing, and people just might hear again more like they did years earlier.

So far, about 60 patients have received the hybrid implant, manufactured by Cochlear Americas. About 10 have had it for more than a year. On standard hearing tests, those patients understand 70 per cent of words a year after the implant - up from 25 per cent before the surgery, Gantz says. That comprehension seems to continue improving as the brain rewires itself to better recognize the electronic signals.

More research is needed before the company seeks Food and Drug Administration approval. But NIH, which is partly funding Gantz's work, and independent specialists call the hybrid implant a potentially important step.

"It addresses patients who are in a very difficult middle ground," says Dr. John Niparko of Johns Hopkins University. "It allows them to perceive the richness of sound through the cochlear zones that are still working," while compensating for the "dead zones."

The brain does have to adjust to decoding electronically generated sound. Users require training, and some describe an echo effect for a few weeks. "It was almost as if I was hearing from two different places," recalls Paula Fuller, 61, of Haver Hill, Iowa.

But within a month of her January 2000 implant, she was hearing sounds she hadn't heard in years - birds chirping, the dialogue in a movie - and no longer avoiding social situations for fear she couldn't converse.

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