A new implantable device uses pulses of light to stimulate auditory nerves, offering an improvement on existing cochlear implants.
Traditional implants rely on a series of electrodes that lie directly against the membrane of the inner ear, and use electrical signals to stimulate the auditory nerves lying beneath. However, implanting them can further damage hearing, and electrical currents can spread easily through the neural tissue to stimulate nearby cells, which the patient hears as noise.
The new work, coordinated by the Swiss Center for Electronics and Microtechnology in Alpnach, Switzerland, builds on the recent discovery of the “optoacoustic effect” – namely, that cells can be stimulated by pulses of infrared light. But exactly how this happens has been a source of some controversy. One theory suggests that it works because rapidly heating nerve cells with light pulses causes them depolarise, triggering an action potential. A competing theory has it that the laser pulses rapidly heat water molecules in the inner ear, causing tiny shockwaves that vibrate the hairs in the same way sound waves normally do.
Now, Nicole Kallweit and her colleagues at Laser Zentrum Hannover in Germany have found evidence for the latter: their system did not work in guinea pigs which had intact auditory nerves but were missing their hair cells. This supports the optoacoustic stimulation theory, they say, and they aim use this refinement of the optoacoustic effect to develop a new generation of cochlear implants. The devices were developed as part of the €4 million Active Implant for Optoacoustic Natural sound enhancement project, partially funded by the EU. Their next focus will be to make the system more energy efficient so that the battery lasts longer. Rather than replace existing cochlear implants, it’s likely that the two technologies will be combined, to give patients a system with greater flexibility that can adapt to their needs over time.
Photo: T.M.O.Pictures / Alamy Stock Photo