Infants Benefit from Implants with More Frequency Sounds

A new study from a UT Dallas researcher demonstrates the importance of considering developmental differences when creating programs for cochlear implants in infants.

Dr. Andrea Warner-Czyz, assistant professor in the School of Behavioral and Brain Sciences, recently published the research in the Journal of the Acoustical Society of America.

“This is the first study to show that infants process degraded speech that simulates a cochlear implant differently than older children and adults, which begs for new signal processing strategies to optimize the sound delivered to the cochlear implant for these young infants,” Warner-Czyz said.

Cochlear implants, which are surgically placed in the inner ear, provide the ability to hear for some people with severe to profound hearing loss. Because of technological and biological limitations, people with cochlear implants hear differently than those with normal hearing.

Think of a piano, which typically has 88 keys with each representing a note. The technology in a cochlear implant can’t play every key, but instead breaks them into groups, or channels. For example, a cochlear implant with 22 channels would put four notes into each group. If any keys within a group are played, all four notes are activated. Although the general frequency can be heard, the fine detail of the individual notes is lost.

Two of the major components necessary for understanding speech are the rhythm and the frequencies of the sound. Timing remains fairly accurate in cochlear implants, but some frequencies disappear as they are grouped.

More than eight or nine channels do not necessarily improve the hearing of speech in adults. This study is one of the first to examine how this signal degradation affects hearing speech in infants.

Infants pay greater attention to new sounds, so researchers compared how long a group of 6-month-olds focused on a speech sound they were familiarized with —“tea”’ — to a new speech sound, “ta.”

The infants spent more time paying attention to “ta,” demonstrating they could hear the difference between the two. Researchers repeated the experiment with speech sounds that were altered to sound as if they had been processed by a 16- or 32-channel cochlear implant.

The infants responded to the sounds that imitated a 32-channel implant the same as when they heard the normal sounds. But the infants did not show a difference with the sounds that imitated a 16-channel implant.

“These results suggest that 6-month-old infants need less distortion and more frequency information than older children and adults to discriminate speech,” Warner-Czyz said. “Infants are not just little versions of children or adults. They do not have the experience with listening or language to fill in the gaps, so they need more complete speech information to maximize their communication outcomes.”

Clinicians need to consider these developmental differences when working with very young cochlear implant recipients, Warner-Czyz said.

Bionic ear technology used for gene therapy

Researchers at UNSW have for the first time used electrical pulses delivered from a cochlear implant to deliver gene therapy, thereby successfully regrowing auditory nerves.

The research also heralds a possible new way of treating a range of neurological disorders, including Parkinson’s disease, and psychiatric conditions such as depression through this novel way of delivering gene therapy.

The research is published today in the prestigious journal Science Translational Medicine.

“People with cochlear implants do well with understanding speech, but their perception of pitch can be poor, so they often miss out on the joy of music,” says UNSW Professor Gary Housley, who is the senior author of the research paper.

“Ultimately, we hope that after further research, people who depend on cochlear implant devices will be able to enjoy a broader dynamic and tonal range of sound, which is particularly important for our sense of the auditory world around us and for music appreciation,” says Professor Housley, who is also the Director of the Translational Neuroscience Facility at UNSW Medicine.

The research, which has the support of Cochlear Limited through an Australian Research Council Linkage Project grant, has been five years in development.

The work centres on regenerating surviving nerves after age-related or environmental hearing loss, using existing cochlear technology. The cochlear implants are “surprisingly efficient” at localised gene therapy in the animal model, when a few electric pulses are administered during the implant procedure.

“This research breakthrough is important because while we have had very good outcomes with our cochlear implants so far, if we can get the nerves to grow close to the electrodes and improve the connections between them, then we’ll be able to have even better outcomes in the future,” says Jim Patrick, Chief Scientist and Senior Vice-President, Cochlear Limited.

It has long been established that the auditory nerve endings regenerate if neurotrophins – a naturally occurring family of proteins crucial for the development, function and survival of neurons – are delivered to the auditory portion of the inner ear, the cochlea.

But until now, research has stalled because safe, localised delivery of the neurotrophins can’t be achieved using drug delivery, nor by viral-based gene therapy.

Professor Housley and his team at UNSW developed a way of using electrical pulses delivered from the cochlear implant to deliver the DNA to the cells close to the array of implanted  electrodes. These cells then produce neurotrophins.

“No-one had tried to use the cochlear implant itself for gene therapy,” says Professor Housley. “With our technique, the cochlear implant can be very effective for this.”

While the neurotrophin production dropped away after a couple of months, Professor Housley says ultimately the changes in the hearing nerve may be maintained by the ongoing neural activity generated by the cochlear implant.

“We think it’s possible that in the future this gene delivery would only add a few minutes to the implant procedure,” says the paper’s first author, Jeremy Pinyon, whose PhD is based on this work. “The surgeon who installs the device would inject the DNA solution into the cochlea and then fire electrical impulses to trigger the DNA transfer once the implant is inserted.”

Integration of this technology into other ‘bionic’ devices such as electrode arrays used in deep brain stimulation (for the treatment of Parkinson’s disease and depression, for example) could also afford opportunities for safe, directed gene therapy of complex neurological disorders.

"Our work has implications far beyond hearing disorders,” says co-author Associate Professor Matthias Klugmann, from the UNSW Translational Neuroscience Facility research team. “Gene therapy has been suggested as a treatment concept even for devastating neurological conditions and our technology provides a novel platform for safe and efficient gene transfer into tissues as delicate as the brain.”

Improved Hearing Anticipated for Implant Recipients

The cochlear implant is widely considered to be the most successful neural prosthetic on the market. The implant, which helps deaf individuals perceive sound, translates auditory information into electrical signals that go directly to the brain, bypassing cells that don’t serve this function as they should because they are damaged.

According to the National Institute on Deafness and Other Communication Disorders, approximately 188,000 people worldwide have received cochlear implants since these devices were introduced in the early 1980s, including roughly 41,500 adults and 25,500 children in the United States.

Despite their prevalence, cochlear implants have a long way to go before their performance is comparable to that of the intact human ear. Led by Pamela Bhatti, Ph.D., a team of researchers at the Georgia Institute of Technology has developed a new type of interface between the device and the brain that could dramatically improve the sound quality of the next generation of implants.

A normal ear processes sound the way a Rube Goldberg machine flips a light switch — via a perfectly-timed chain reaction involving a number of pieces and parts. First, sound travels down the canal of the outer ear, striking the eardrum and causing it to vibrate. The vibration of the eardrum causes small bones in the middle ear to vibrate, which in turn, creates movement in the fluid of the inner ear, or cochlea. This causes movement in tiny structures called hair cells, which translate the movement into electrical signals that travel to the brain via the auditory nerve.

Dysfunctional hair cells are the most common culprit in a type of hearing loss called sensorineural deafness, named for the resulting breakdown in communication between the ear and the brain. Sometimes the hair cells don’t function properly from birth, but severe trauma or a bad infection can cause irreparable damage to these delicate structures as well.

Contemporary cochlear implants

Traditional hearing aids, which work by amplifying sound, rely on the presence of some functioning hair cells. A cochlear implant, on the other hand, bypasses the hair cells completely. Rather than restoring function, it works by translating sound vibrations captured by a microphone outside the ear into electrical signals. These signals are transmitted to the brain by the auditory nerve, which interprets them as sound.

Cochlear implants are only recommended for individuals with severe to profound sensorineural hearing loss, meaning those who aren’t able to hear sounds below 70 decibels. (Conversational speech typically occurs between 20 and 60 decibels.)

The device itself consists of an external component that attaches via a magnetic disk to an internal component, implanted under the skin behind the ear. The external component detects sounds and selectively amplifies speech. The internal component converts this information into electrical impulses, which are sent to a bundle of thin wire electrodes threaded through the cochlea.

Improving the interface

As an electrical engineer, Bhatti sees the current electrode configuration as a significant barrier to clear sound transmission in the current device.

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

Contemporary implants contain between 12 and 22 wire electrodes, each of which conveys a signal for a different pitch. The idea is the more electrodes, the clearer the message.

So why not add more wire electrodes to the current design and call it a day?

Much like house-hunting in New York City, the problem comes down to a serious lack of available real estate. At its widest, the cochlea is 2 millimeters in diameter, or about the thickness of a nickel. As it coils, it tapers down to a mere 200 micrometers, about the width of a human hair.

"While we’d like to be able to increase the number of electrodes, the space issue is a major challenge from an engineering perspective," says Bhatti.

With funding from the National Science Foundation, Bhatti and her team have developed a new, thin-film, electrode array that is up to three times more sensitive than traditional wire electrodes, without adding bulk.

Unlike wire electrodes, the new array is also flexible, meaning it can get closer to the inner wall of the cochlea. The researchers believe this will create better coupling between the array and the nervous system, leading to a crisper signal.

According to Bhatti, one of the biggest challenges is actually implanting the device into the spiral-shaped cochlea:

"We could have created the best array in the world, but it wouldn’t have mattered if the surgeon couldn’t get it in the right spot," says Bhatti.

To combat this problem, the team has invented an insertion device that protects the array and serves as a guide for surgeons to ensure proper placement.

Before it’s approved for use in humans, it will need to undergo rigorous testing to ensure that it is both safe and effective; however, Bhatti is already thinking about what’s next. She envisions that one day, the electrodes won’t need to be attached to an array at all. Instead, they will be anchored directly to the cochlea with a biocompatible material that will allow them to more seamlessly integrate with the brain.

The most important thing, according to Bhatti, is not to lose sight of the big picture.

"We are always designing with the end-user in mind," says Bhatti. "The human component is the most important one to consider when we translate science into practice."

Now hear this: Researchers identify forerunners of inner-ear cells that enable hearing

Researchers at the Stanford University School of Medicine have identified a group of progenitor cells in the inner ear that can become the sensory hair cells and adjacent supporting cells that enable hearing. Studying these progenitor cells could someday lead to discoveries that help millions of Americans suffering from hearing loss due to damaged or impaired sensory hair cells.

“It’s well known that, in mammals, these specialized sensory cells don’t regenerate after damage,” said Alan Cheng, MD, assistant professor of otolaryngology. (In contrast, birds and fish are much better equipped: They can regain their sensory cells after trauma caused by noise or certain drugs.) “Identifying the progenitor cells, and the cues that trigger them to become sensory cells, will allow us to better understand not just how the inner ear develops, but also how to devise new ways to treat hearing loss and deafness.”

The research was published online Feb. 26 in Development. Cheng is the senior author. Former medical student Taha Jan, MD, and postdoctoral scholar Renjie Chai, PhD, share lead authorship of the study. Roel Nusse, PhD, a professor of developmental biology, is a co-senior author of the research.

The inner ear is a highly specialized structure for gathering and transmitting vibrations in the air. The auditory compartment, called the cochlea, is a snail-shaped cavity that houses specialized cells with hair-like projections that sense vibration, much like seaweed waving in the ocean current. These hair cells are responsible for both hearing and balance, and are surrounded by supporting cells that are also critical for hearing.

Twenty percent of all Americans, and up to 33 percent of those ages 65-74, suffer from hearing loss. Hearing aids and, in severe cases, cochlear implants can be helpful for many people, but neither address the underlying cause: the loss of hair cells in the inner ear. Cheng and his colleagues identified a class of cells called tympanic border cells that can give rise to hair cells and the cells that support them during a phase of cochlear maturation right after birth.

“Until now, these cells have had no clear function,” said Cheng. “We used several techniques to define their behavior in cell culture dishes, as well as in mice. I hope these findings will lead to new areas of research to better understand how our ears develop and perhaps new ways to stimulate the regeneration of sensory cells in the cochlea.”

Mass. Eye and Ear Researchers Regenerate Sensory Hair Cells, Restore Hearing to Noise-Damaged Ears

Hearing loss is a significant public health problem affecting almost 50 million people in the United States alone. Sensorineural hearing loss is the most common form and is caused by the loss of sensory hair cells in the cochlea. Hair cell loss results from a variety of factors including noise exposure, aging, toxins, infections, and certain antibiotics and anti-cancer drugs.  Although hearing aids and cochlear implants can ameliorate the symptoms somewhat, there are no known treatments to restore hearing, because auditory hair cells in mammals, unlike those in birds or fish, do not regenerate once lost. Auditory hair cell replacement holds great promise as a treatment that could restore hearing after loss of hair cells.

In the Jan. 10 issue of Neuron, Massachusetts Eye and Ear and Harvard Medical School researchers demonstrate for the first time that hair cells can be regenerated in an adult mammalian ear by using a drug to stimulate resident cells to become new hair cells, resulting in partial recovery of hearing in mouse ears damaged by noise trauma. This finding holds great potential for future therapeutic application that may someday reverse deafness in humans.

“Hair cells are the primary receptor cells for sound and are responsible for the sense of hearing,” explains senior author, Dr. Albert Edge, of Harvard Medical School and Mass. Eye and Ear. “We show that hair cells can be generated in a damaged cochlea and that hair cell replacement leads to an improvement in hearing.”

In the experiment, the researchers applied a drug to the cochlea of deaf mice. The drug had been selected for its ability to generate hair cells when added to stem cells isolated from the ear. It acted by inhibiting an enzyme called gamma-secretase that activates a number of cellular pathways. The drug applied to the cochlea inhibited a signal generated by a protein called Notch on the surface of cells that surround hair cells. These supporting cells turned into new hair cells upon treatment with the drug. Replacing hair cells improved hearing in the mice, and the improved hearing could be traced to the areas in which supporting cells had become new hair cells.

“The missing hair cells had been replaced by new hair cells after the drug treatment, and analysis of their location allowed us to correlate the improvement in hearing to the areas where the hair cells were replaced,” Dr. Edge said.

This is the first demonstration of hair cell regeneration in an adult mammal.  “We’re excited about these results because they are a step forward in the biology of regeneration and prove that mammalian hair cells have the capacity to regenerate,” Dr. Edge said. “With more research, we think that regeneration of hair cells opens the door to potential therapeutic applications in deafness.”

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.