Deaf girl fitted with bionic ear speaks her first word

Evie was born profoundly deaf but it was not until she was 16 months old that tests revealed she had no hearing nerves, meaning an auditory brainstem implant - or bionic ear - was her only chance of ever hearing.

The 23-month-old has Oculo-Auriculo-Vertebral Syndrome (OAV), a very rare condition with no known cause, which affects the eyes, ears and spine.

Cochlear implants — electronic devices surgically implanted in the ear to help provide a sense of sound — have been successfully used since the late 1980’s. But questions remain as to whether bilateral cochlear implants, placed in each ear rather than the traditional single-ear implant, are truly able to facilitate binaural hearing. Now, Tel Aviv University researchers have proof that under certain conditions, this practice has the ability to salvage binaural sound processing for the deaf and hard-of-hearing.

According to Dr. Yael Henkin of TAU’s Department of Communication Disorders at the Stanley Steyer School of Health Professions and Head of The Hearing, Speech, and Language Center at Sheba Medical Center, and her colleagues Prof. Minka Hildesheimer, Yifat Yaar-Soffer, and Lihi Givon, the brain unites incoming sound from each ear at the brainstem through what is called “binaural processing.” “When we hear with both ears, we have an efficient auditory system,” she explains. Binaural processing provides improved ease of listening, sound localization, and the ability to understand speech in noisy surroundings.

In their study, the researchers looked at children who had lost their hearing at a young age and were not born deaf. Those who were provided with bilateral cochlear implants exhibited true binaural processing, similar to that of their normal hearing peers. In contrast, deaf-at-birth children who received their first cochlear implant at young age and their second after long delay, did not exhibit binaural processing.

The research was recently reported in the journal Cochlear Implants International.

Stem Cells Turn Hearing Back On

Scientists have enabled deaf gerbils to hear again—with the help of transplanted cells that develop into nerves that can transmit auditory information from the ears to the brain. The advance, reported in Nature, could be the basis for a therapy to treat various kinds of hearing loss.

In humans, deafness is most often caused by damage to inner ear hair cells—so named because they sport hairlike cilia that bend when they encounter vibrations from sound waves—or by damage to the neurons that transmit that information to the brain. When the hair cells are damaged, those associated spiral ganglion neurons often begin to degenerate from lack of use. Implants can work in place of the hair cells, but if the sensory neurons are damaged, hearing is still limited.

"Obviously the ultimate aim is to replace both cell types," says Marcelo Rivolta of the University of Sheffield in the United Kingdom, who led the new work. "But we already have cochlear implants to replace hair cells, so we decided the first priority was to start by targeting the neurons."

In the past, scientists have tried to isolate so-called auditory stem cells from embryoid bodie—aggregates of stem cells that have begun to differentiate into different types. But such stem cells can only divide about 25 times, making it impossible to produce them in the quantity needed for a neuron transplant.

Rivolta and his colleagues knew that during embryonic development, a handful of proteins, including fibroblast growth factor (FGF) 3 and 10, are required for ears to form. So they exposed human embryonic stem cells to FGF3 and FGF10. Multiple types of cells formed, including precursor inner-ear hair cells, but they were also able to identify and isolate the cells beginning to differentiate into the desired spiral ganglion neurons. Then, they implanted the neuron precursor cells into the ears of gerbils with damaged ear neurons and followed the animals for 10 weeks. The function of the neurons was restored.

"We’ve only followed the animals for a very limited time," Rivolta says. "We want to follow them long-term now"—both to assess the possibility of increased cancer risk and to observe the long-term function of the new neurons, he adds.

"It’s very exciting," says neuroscientist Mark Maconochie of Sussex University in the United Kingdom, who was not involved in the new work. "In the past, there has been work where someone makes a single hair cell or something that looks like one neuron [from stem cells], and even that gets the field excited. This is a real step change."

The question now, he says, is whether the procedure can be fine-tuned to allow more efficient production of the relay neurons—currently, fewer than 20% of the stem cells treated develop into those ear neurons. By combining growth factors other than FGF3 and FGF10 with the stem cell mix, researchers could harvest even more ear progenitor cells, he hypothesizes.

"The next big challenge will be to do something as effective as this for the hair cells," Maconochie adds.