Hearing Manipulated By Electronics

The technique which is described in an article in the journal Nature Materials represents a breakthrough for the machine-to-brain interface, with opportunities for greater symbiosis between electronics and biological systems.

“In the future we envisage a wirelessly controlled and permanent implant”, says Magnus Berggren, Professor of Organic Electronics at LiU and one of the authors of the article.

The small electrically charged organic molecules that transmit signals between nerve cells are known as neurotransmitters. The most important substance in the cochlea is glutamate, which regulates signals from the inner hair cells to the auditory nerve. But excessive quantities of glutamate can be toxic and lead to cell depletion.

To test their idea of selectively transporting neurotransmitters electronically the researchers used the hearing organ in guinea pigs as a model system. The tip of an ion pump, with similar design to a small syringe, was inserted in animals under anaesthesia near the membrane in the inner ear called the round window. When the power was switched on exact doses of glutamate were delivered via an electrically charged plastic film and diffused through the round window to the intended target, the hair cells.

By measuring the auditory response of the brainstem the researchers were able to study what was happening as the transport of glutamate was taking place.  After one hour the glutamate concentration reached levels where the result was loss of hearing.

The tests show how the ion pump can be used to control the supply of neurotransmitters and to direct them to specific cell types.

Osmotic pumps are today used to transport the substances in a liquid, risking over-dosage, leaking and excessive pressure in small spaces, for example in the cochlea

“The ability to deliver exact doses of signal substances creates brand new opportunities for future corrections of signal systems that fail in many neurological illnesses”, says Professor Agneta Richter-Dahlfors at KI, who together with Magnus Berggren is leading the research at the SSF financed OBOE Center.  Tests on guinea pigs were carried out in Barbara Canlons laboratories at Karolinska Institutet.