Brainstem Implants Bringing Sound to Some Children

 
Three months after receiving an ABI, Angelica is learning to associate new sounds with their meanings through intensive therapy. | Keck Medicine of USC

Cochlear implants have transformed hearing options for people born deaf or with severe hearing impairments, but they don't work for everyone. Now, researchers at the Keck School of Medicine of the University of Southern California and Children's Hospital Los Angeles are testing another, more invasive device called an auditory brainstem implant (ABI) in a small group of children for the first time.

The clinical trial began in March 2014 with the aim of testing the device's safety and feasibility. The full trial eventually will include 10 children, and so far four children have had an ABI surgically implanted. At a press briefing at the 2015 AAAS Annual Meeting, Eric Wilkinson, an otolaryngologist from the House Clinic and an investigator on the trial, estimated that nearly 100 children in the U.S. each year might benefit from an ABI.

Cochlear implants are electronic devices that are placed in the ear and mimic the auditory wiring there, a procedure that requires a functioning cochlear nerve. An auditory brainstem implant is placed deep within the brain itself, with a receiver fitted under the scalp and a millimeters-long electrode that lays on top of and directly stimulates a section of the brainstem called the cochlear nucleus.

So far, the device has only been approved by the U.S. Food and Drug Administration for adults with tumors on the nerve that transmits information from the inner ear to the brain. The Keck researchers hope to find out more about whether ABI surgery is safe and possible to do in children. The procedure is technically difficult, said House Clinic surgeon Marc Schwartz, "and we have to provide parents with the information to determine whether it's worthwhile to go through an operation like this."

When children first receive their ABIs, they hear things like a newborn baby might, said Laurie Eisenberg, a USC pediatric audiologist. The device produces a sort of "pixilated" signal from the brainstem that isn't sorted into the normal acoustic patterns detected by hearing people. "The incoming stimulus for a child with an ABI is completely scrambled, and as a result, children with ABI require intensive long-term therapy and very strong parental involvement," Eisenberg said.

"It's a myth to assume that the device goes in and the kid starts to figure out how to interpret the sounds," agreed Nan Ratner, a professor of hearing and speech sciences from the University of Maryland. "It's an awful lot of education and therapy that has to go along so that the child can reconcile the cues that they see on people's faces with the noises that they're hearing."

In patients where ABIs work best, the device could provide a sound signal "that's enough to follow a conversation and even to speak on the telephone," said Robert Shannon, an otolaryngology research at USC.