Novel Interface Could Lead to Improved Cochlear Implants

Despite their importance, cochlear implants leave much to be desired. But now, a group of researchers at the Georgia Institute of Technology has created a new interface between the device and the brain that could eventually lead to the development of hearing aids with improved sound quality.

In a condition known as sensorineural deafness, hearing loss is most often caused by dysfunctional hair cells. However, while traditional hearing aids rely on hair cells to amplify sound, cochlear implants bypass the hair cells, translating sound vibrations captured using a microphone outside the ear into electrical signals.

Such devices consist of an external component that uses a magnetic disk to attach it to an internal component implanted under the skin behind the ear. The external component detects sounds and selectively amplifies speech, while the internal component converts this information into electrical impulses, which are sent to a bundle of thin wire electrodes threaded through the cochlea. This electrode configuration, according to Pamela Bhatti, an assistant professor in the School of Electrical and Computer Engineering at Georgia Tech, is a significant barrier to clear sound transmission.

"In an intact ear, the hair cells are plentiful and are in close contact with the nerves that transmit sound information to the brain," Bhatti explains. "The challenge with the implant is getting efficient coupling between the electrodes and the nerves."

Today's cochlear implants contain between 12 and 22 wire electrodes, each of which conveys a signal for a different pitch. More electrodes should result in a clearer message. However, the cochlea measures only 2 mm in diameter, shrinking down to 200 mm as it coils. "While we'd like to be able to increase the number of electrodes, the space issue is a major challenge from an engineering perspective," Bhatti remarks.

To answer this challenge, Bhatti and her team have developed a thin-film, electrode array that is up to three times more sensitive but no more bulky than traditional wire electrodes. And unlike wire electrodes, the new array is also flexible, enabling it to be placed closer to the inner wall of the cochlea. The researchers believe that this feature will create a better link between the array and the nervous system, improving signal quality.