Hear the light?

Infrared light stimulates the work of neurons in the inner ear no worse than sound waves – this discovery was made by researchers from the American Northwestern University (Northwestern University). New types of cochlear implants based on this phenomenon will significantly improve the lives of deaf people.

In a healthy inner ear, hair cells that respond to sound cause neurons to work, which forward signals to the brain.

However, these receptors can be damaged due to illness or some kind of injury, as well as a birth defect. All this leads to deafness.

But modern medicine can cope with this problem: people are fitted with cochlear implants that act directly on neurons.

Today, these devices allow a deaf child to learn to speak almost as well as a healthy one. Of course, hearing cannot be called ideal, in particular, users of such implants perceive music poorly, it is difficult for them to communicate in conditions of heavy noise and with native speakers of tonal languages like Mandarin Chinese.

This is understandable, because unlike three thousand hair cells in a healthy ear, the implant provides only about 20 neurons.

A larger number of electrodes (many more than 20) would significantly improve the sound perception of deaf people.

But it is not possible to implement this in practice, since the tissues conduct electricity and the signals from different electrodes begin to interfere.

At the same time, it is easier to direct the laser light precisely at the nerve, it does not spread in all directions. Thus, the implant can provide neurons with a large amount of information.

To test this idea, Klaus-Peter Richter and his colleagues directed infrared light directly at neurons in the inner ear of deaf guinea pigs. In parallel, scientists recorded a picture of electrical activity in the lower mound, the area of the brain located between the inner ear and the cerebral cortex.

The resulting "maps" tell quite well about the quality of the sound coming into the ear, and, accordingly, about the amount of information coming into the brain.

If we compare the work of old cochlear implants and new technology, then in the first case the drawings are blurred, and in the second case they have clear contours, like in healthy guinea pigs. This is exactly what biologists reported at the Medical Bionics conference held recently in Lorne, Australia.

It remains a mystery how light excites neurons, because there are no photosensitive proteins in them. Richter believes that an important role is played by the heat that "accompanies" infrared radiation.

Note that initially this phenomenon was discovered by surgeons who tried to connect nerves with a laser.

At the moment, scientists are trying to establish how prolonged heating affects neurons. If no negative effects are detected, they plan to create an optical fiber and lasers capable of conducting light directly into the inner ear.

The membrane according to the materials of New Scientist

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27.11.2008