One of the latest videos to go viral on the Web lets us all witness a little miracle: two-year-old “Cooper,” deaf since birth and just fitted with a cochlear implant, hears his mother’s voice for the first time. It is an emotionally charged reminder of the difference these devices have made in so many lives and speaks directly to one of the biggest obstacles to greater application of cochlear implants: how to tell if they’re working.
The Original Brain-Machine Interface
A cochlear implant (CI) converts sounds into electrical signals that activate nerve cells in the brain’s auditory cortex—what the cochlea normally does, but in a much more rudimentary way. Implants have altered the landscape for treating hearing loss and are now the most common treatment for congenital deafness. More broadly, their success has fueled hope for new technologies that convert external stimuli to neural code—or vice versa, as in current efforts to control computers and robots with thoughts alone.
But cochlear implants are far from perfect. “It’s wonderful technology, but it doesn’t solve all the problems of hearing loss,” says John S. Oghalai, a neuroscientist at Stanford University who has spent much of his career trying to make cochlear implants work better for more people. (Read the full Q&A with Oghalai.)
Finding the Right Nerve Cells
A cochlear implant is only as good as its programming. Its electrical impulses need to stimulate the right nerve cells in order for hearing to be clear enough to comprehend speech. Right now, there’s no objective way to tell whether that’s happening. Doctors do their best based on previous experience combined with patient feedback.
The problem is that children who were born deaf can’t always tell you if it’s working—they don’t know what sound is. Instead, doctors rely on behavioral clues, the kinds of responses that Cooper showed in the video. This becomes difficult or impossible in children with developmental disabilities in addition to deafness—an increasingly common situation as preterm-birth rates rise worldwide—who may not show any behavioral reaction.
How do you know if CI stimulation is reaching the right cells? Functional MRI could tell you, but it is contraindicated in people with cochlear implants. Near-Infrared Spectroscopy (NIRS), an older imaging technique that is being applied to cochlear implant research for the first time, has shown promise in preliminary data from a study spearheaded by Oghalai and funded by the Dana Foundation.
Oghalai’s Stanford research group is also running a prospective clinical trial, funded by the National Institutes of Health, to try to better guide clinical decision-making in deaf children with development delays. Children will randomly receive either a cochlear implant or hearing aid, and researchers will track speech development, learning, and quality-of-life outcomes over five years.
“We hope to get more objectivity to provide evidence-based medicine for these children and better counsel parents about what they’re getting into with a cochlear implant,” Oghalai says.
--Brenda Patoine, science writer
Dana’s grantee Q&As are published quarterly and can be found here.