Ear implant aims to delve deeper

From: BBC News, UK - Jan 7, 2004

A new type of ear implant may work better by placing electrodes inside the brain stem itself.

US surgeons have now finished putting the implants into the first two patients, reports New Scientist.

The operation to place the implant is potentially riskier than one involving a standard cochlear implant - but the results may be better for patients.

The procedure could help people who have lost their auditory nerve through cancer - or who were born without one.

Normal cochlear implants place electrodes in various locations against the outside of the brain stem.

The implant receives sound signals such as speech, and converts them into electrical signals which stimulate cells near the surface of this brain region.

However, the cells which are designed to deal with sound signals at certain frequencies are not found near the surface, but instead are deeper inside.

This means that while some patients get excellent results from these implants, actually being able to interpret speech to a degree, others find that the implants can assist lip-reading, but cannot be used independently to listen to someone talking.

Electrode inside

Scientists at the House Ear Institute in Los Angeles believe that by placing the electrodes inside, rather than on the surface, it might be possible to pass on a wider range of frequencies, improving the recognition of different speech tones.

The risks are clear - the "cochlear nucleus", which is targeted by the operation, is close to brain areas that are important for operation of facial nerves and those controlling the voicebox and swallowing, and adjacent to major blood vessels supplying the brain.

The Los Angeles team, led by Dr Bob Shannon, have developed electrodes shaped so they do not cut or crush vital brain cells as they are pushed into position.

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

Nerveless

The technique might possibly be useful for people who have no auditory nerve - they are either born without one, or have lost their due to the removal of a particular type of cancer.

However, despite the excitement over the technique, there is no evidence yet that it can work well.

So far two deaf women have undergone the procedure in the US - and the only available results, for the first of these, suggest that only one of the eight electrodes implanted within the brain stem is functioning properly.

Richard Ramsden, a surgeon from the Manchester Royal Infirmary who specialises in cochlear implant operations, said that he would want to see evidence that it worked before attempting a similar operation himself.

He said: "The technique is exciting and new, but we don't know if it works yet.

"There are risks involved, and the operation should only be carried out by very experienced surgeons to minimise that."

© BBC MMIV