Hearing implant harnesses platinum and iridium

From: Platinum today, UK - Jan 15, 2004

Doctors have highlighted a new surgical procedure to restore hearing in deaf people that utilises activated iridium implants to directly stimulate nerve cells.

For the first time surgeons have placed the implants directly on the brain stem - a risky procedure as the stem carries signals from the entire body to the brain.

"If you damage the brain's cortex it's not that big a deal. But at the brainstem level every neuron you damage could damage function," Bob Shannon, the surgeon behind the procedure told New Scientist.

"We took 15 years to convince ourselves that this could be done safely."

Feeding auditory signals directly into the brainstem should work better than implants that sit just off it.

Problems with the sound-detecting hair cells in the cochlea in the ear cause most deafness but while cochlear implants can bypass these hair cells and stimulate the auditory nerve directly, they cannot help people with a damaged cochlea or auditory nerve.

The implant contains eight micro-electrodes made of activated iridium with platinum lead wires.

The eight electrodes of varying lengths are able to stimulate several bundles of nerves so that different sound frequencies can be detected.

Dr Shannon, who works at the Home Ear Institute, explained the shape of the electrode is key to the procedure. After conducting experiments with animals an electrode the shape of a pencil tip was found to be most effective.

Although only one electrode worked on the first patient (an American woman) to undergo the procedure, Dr Shannon hopes to be able to get four working in future operations - enough for a person to understand speech.

One successfully attached electrode does however improve lip-reading ability by 30 per cent, Dr Shannon added.

The procedure has been received warmly in the UK with Stuart Rosen, a speech and hearing specialist at University College London, suggesting it has the potential to dramatically improve the quality of some deaf people's lives.

Richard Ramsden from Manchester Royal Infirmary also explained it could be used to help congenitally deaf children born without a cochlear nerve.

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