INFRARED light could lead to better CI's?

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source: bhNEWS

New Scientist magazine - November 20, 2008

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Light opens up a world of sound for the deaf

a.. By Nowak

INFRARED light can stimulate neurons in the inner ear as precisely as

sound waves, a discovery that could lead to better cochlear implants

for deaf people.

A healthy inner ear uses hair cells that respond to sound to stimulate

neurons that send signals to the brain. But hair cells can be

destroyed by disease or injury, or can contain defects at birth,

leading to deafness. In such cases, cochlear implants can directly

stimulate neurons.

The hearing provided by today's implants is good enough to enable deaf

children to develop speech skills that are remarkably similar to

hearing children's. Implant users still find it tough to appreciate

music, communicate in a noisy environment and understand tonal

languages like Mandarin, however. That's because the implants use only

20 or so electrodes, a small number compared to the 3000-odd hair

cells in a healthy ear.

More sources of stimulation should make hearing clearer but more

electrodes cannot be packed in because tissue conducts electricity, so

signals from different electrodes would interfere. In contrast, laser

light targets nerves more precisely and doesn't spread, which could

allow an implant to transmit more information to the neurons.

To explore this idea, a team led by Claus- Richter at

Northwestern University in Chicago shone infrared light directly onto

the neurons in the inner ear of deaf guinea pigs. At the same time,

the researchers recorded electrical activity in the inferior

colliculus, a relay between the inner ear and the brain cortex,

producing a set of frequency " maps " . These maps are a good indication

of the quality of sound information sent to the brain.

Electrical stimulation of the inner ear by a cochlear implant produces

blurred maps, but the light stimulation produced maps that were as

sharp as those produced by sound in hearing guinea pigs, says Richter,

who presented the findings at the Medical Bionics conference in Lorne,

in the Australian state of , earlier this week.

Light stimulation produced frequency maps as sharp as those produced

by sound in hearing guinea pigs It is a mystery how light stimulates

the neurons, as they do not contain light-sensitive proteins. The

phenomenon was discovered by surgeons attempting to " weld " nerves with

heat from a laser. Richter says the heat that accompanies the light

may play a role, and his team is now investigating the long-term

effects of heating neurons.

Making fibre optics and lasers to target light in the inner ear is the

next challenge.