Brainstem implants help kids born without auditory nerves
Much has been mentioned in the news lately about hope for those with hearing loss or hearing impairment in the form of auditory brainstem technology, but is it for everyone? Results from use in Europe over the past 10 years and more recent clinical trials here in the U.S. show certain populations will derive greater benefit from the technology than others. While the technology is not for everyone, for others it could be life changing.
For children who were either born without the auditory nerve or who have damage to the auditory nerve, cochlear implants and hearing aids are ineffective. That is where auditory brainstem implants come in; they work by bypassing both the inner ear and the auditory nerve and stimulating the brainstem directly. Other conditions which could be helped with ABI technology include those with temporal bone fracture, severe calcification of the cochlea from meningitis or congenital aplasia (damage from birth) of the cochlea or cochlear nerve.
Auditory brainstem implants have been used on children in Europe for over 10 years. Unfortunately they lack regulatory approval as of yet in the U.S. except for those over the age of 12 with a specific condition called neurofibromatosis type II, and there has been extremely limited success with that group. Given that results in Europe on younger children have been effective but results in the U.S., on older children and adults, have not, scientists are looking to the developing brain for answers. The possible reason might be that brains are less formative as we age; the brain is simply not as adaptable to language as in those who are younger. The collective thinking is the earlier a child receives an ABI, i.e. while the brain is still flexible and adaptable, the more successful the treatment will be.
An ongoing FDA-approved clinical trial supported by a National Institutes of Health grant at the University of Southern California’s Keck School of Medicine, begun in March of 2014, has thus far treated five out of an anticipated 10 participants with auditory brainstem implants. In order to be eligible for participation in the clinical trial, children must be between the ages of two and five, and have been born without auditory nerves. In addition, previous attempts to use cochlear implants and hearing aids must have failed. Overall, the clinical trial has two major goals: to prove the ABI surgery is safe for young children and for the researchers to study how the brain develops over time with regard to speech and sound. Thus far the trial has netted positive results.
“The children in this study are under five years of age,” said Keck School of Medicine Professor Robert Shannon, an investigator for the trial and leading scientist in the development of ABI technology since 1989. “When a child is born, their ear is hard-wired for sound, but the brain has to learn how to perceive sound and speech from the information coming up the hearing pathway. If the ear is not providing sound information to the brain, the hearing part of the brain doesn’t develop properly. The ABI provides sound to these pathways so they grow and develop with the child.”
Here’s how it works: The ABI is essentially a tiny paddle, only 8x3 mm, that has a panel of 21 electrodes attached. After being surgically attached to the brainstem (the surgery takes about 6 hours) the ABI interfaces with the cochlear nucleus, which is the first relay station in the brain stem. The researchers are then able to map exactly which of the 21 electrodes offer auditory stimulation to the brain stem, as opposed to tactile stimulation. The electrodes offering non-auditory stimulation are then switched off, leaving only auditory stimulation behind.
ABIs are not an immediate fix, however. Just like how infants learn to process and interpret the sounds they hear over time, the recipient of an ABI needs time to learn to do the same. He also needs training and a strong family support system. The good news is in European cases, the younger children that have received ABIs have shown progress in both auditory and speech development that is on par with their peers that have cochlear implants, and have shown improvement in their cognitive development as well.
“Initial activation of the ABI is like a newborn entering the world and hearing for the first time, which means these children will need time to learn to interpret what they are sensing through the device as ‘sound,’” said audiologist Laurie Eisenberg, Ph.D., a Keck School of Medicine otolaryngology professor and study co-leader. “All of our study participants whose ABIs have been activated are progressing at expected or better rates. We are optimistic that, with intensive training and family support, these children will eventually be able to talk on the phone.”