Hearing loss may change brain structure

"In the case of tinnitus, surprisingly, there were few changes to brain structure despite changes to function, suggesting that when sensory deprivation is accompanied by self-generated noise, it may be better at preserving neural tissue," says Fatima Husain.

Researchers used two different imaging modalities in studies of people with hearing loss, normal hearing, and those with hearing loss and tinnitus (ringing in the ears).

People in the hearing loss group showed structural changes in their brains.

“This suggests that functional changes due to sensory deprivation may result in long-term structural changes,” says Fatima Husain, a Beckman Institute faculty member at the University of Illinois.

The goal of the study was to investigate structural gray and white matter changes related to tinnitus and hearing loss and try to dissociate them from changes due only to hearing loss. (Credit: Fatima Husain)

“However, in the case of tinnitus, surprisingly, there were few changes to brain structure despite changes to function, suggesting that when sensory deprivation is accompanied by self-generated noise, it may be better at preserving neural tissue.”

Husain and her collaborators on the study measured neuroanatomical changes in gray and white matter in the brains of participants with only bilateral hearing loss (HL), participants who had HL and tinnitus (TIN), and a control group with normal hearing (NH) without tinnitus.

Their study, reported in the journal Brain Research, looked at neuroanatomical alterations associated with hearing loss and tinnitus.

Read the original study DOI: 10.1016/j.brainres.2010.10.095

The researchers used structural magnetic resonance imaging (MRI) scans and voxel-based morphometry (VBM) to examine changes in gray matter, and diffusion tensor imaging (DTI), to identify changes in white matter tract orientation.

While tinnitus is often accompanied by hearing loss, not everyone with hearing loss experiences tinnitus.

The goal of the study was to investigate structural gray and white matter changes related to tinnitus and hearing loss and try to dissociate them from changes due only to hearing loss.

“We observed that the HL group had the most profound changes in both white and gray matter relative to the other groups,” Husain says. The gray matter decreases seen in the HL group relative to the NH group were in the anterior cingulate, putamen, and middle frontal gyrus.

Two of these regions, the anterior cingulate and frontal cortex, were “also implicated in our companion study that studied functional response of the brain in the same group of subjects and points to involvement of the attention processing network.”

By dissociating the effect of tinnitus from hearing loss, the researchers concluded that “hearing loss rather than tinnitus had the greatest influence on gray and white matter alterations.”

Husain directs the Auditory Cognitive Neuroscience Lab in the Department of Speech and Hearing Science.

More news from the University of Illinois: http://www.beckman.illinois.edu/index.aspx

Hearing Disability Linked To Poor Touch Sensitivity

Touch and hearing are very distinct, but German scientists have found a possible genetic link between the two sensory systems.

Superficially, the two senses might seem worlds apart, but both rely on the ability to translate motions - vibrations in the ear and movement and pressure on the skin - into signals to the brain. A common set of molecules or mechanisms might be at work.

To determine if touch sensitivity can be inherited genetically, Henning Frenzel of the Max-Delbruck Center for Molecular Medicine and his colleagues first examined 100 pairs of fraternal and identical twins in a study outlined in the journal PLoS Biology.

They tested the twins on two kinds of touch sensitivity traits: "vibration detection threshold," or how low a vibration the subject could detect with their pinky finger; and "tactile acuity," or the ability to distinguish between two pressure points on the skin that are very close together.

Since the identical twins are genetically identical and the fraternal twins share up to 50 percent of the same genes, any genetic effect on touch should be more pronounced in the former.

Next, Frenzel and his team calculated the heritability of the two traits, a figure that explains the degree to which genetic variation contributed to the variation in the traits seen in the subjects. On average, 28 percent of the differences in tactile acuity and 52 percent of the differences in vibration detection could be chalked up to genetic influence.

Second Experiment
In a second experiment, the scientists found that some - but not all - of a population of young people that were born deaf also had impaired tactile acuity. But since there are about 70 known genes that are involved in hearing impairment, the researchers wanted to focus on a smaller group of genes to test the link between hearing and touch impairment.

Third Experiment - Usher syndrome
The scientists next examined patients with Usher syndrome - a hereditary condition that causes both hearing and visual impairment. They zeroed in on USH2A, one of the nine known genes that, when mutated, cause Usher syndrome.

Of the Usher patients studied, the 19 individuals that had a mutation in USH2A had both impaired hearing and poor touch sensitivity. It's possible then, that this gene may play a role in both touch and sound.

"Our next task will be to investigate some of these other cases to see if they are also correlated with problems in touch," senior author Gary Lewin said in a statement Tuesday. "This will give us a better understanding of the genetic mechanisms that underlie both types of perception."

Middle ear microphone aims to improve cochlear implants

U.S researchers are developing a tiny middle ear "microphone" that could remove the need for any external components on cochlear implants.

Led by University of Utah engineer Darrin J. Young, the research team has produced and tested a prototype of the device which uses an accelerometer attached to the tiny bones of the middle ear to detect sound vibration.

Conventional cochlear implants use an externally worn microphone, speech processor and electromagnetic transmitter, along with an implanted receiver and stimulator that's wired to the auditory nerves.

When sounds are picked up by the microphone and transmitted to the nerves via the internal stimulator, the patient hears.

While it has given hearing to hundreds of thousands of people around the world, this approach still has its drawbacks in terms of practicality, reliability and social perception.

“It’s a disadvantage having all these things attached to the outside” of the head, Young says. “Imagine a child wearing a microphone behind the ear. It causes problems for a lot of activities. Swimming is the main issue. And it’s not convenient to wear these things if they have to wear a helmet.”

While the conventional design doesn't make use of the ear canal and eardrum, Young's device does. It consists of a speech processor and transmitter implanted under the skin of the skull along with an accelerometer and a low-power silicon chip attached to the umbo (the point at which the eardrum connects to the three tiny ear bones).

This enables it to detect vibration of the eardrum (as occurs in normal hearing). From there the system acts like a conventional cochlear implant, transmitting vibrations as electrical signals to electrodes in the cochlea.

The use of an accelerometer rather is a key to the design. Unlike standard microphones that use a diaphragm to detect sound vibrations, the accelerometer won't become clogged by growing tissue when implanted.

There is also a caveat - users would still have to wear a charger behind the ear while asleep to recharge the battery.

Researchers found that the implant works best if the incus (anvil bone) is first removed surgically.

Young says tests in people are about three years away and has created this recording (with output going to a speaker rather than implanted electrodes) to demonstrate the device. Recognize the tune?

The research is published online in the Institute of Electrical and Electronics Engineers journal Transactions on Biomedical Engineering.

Source: University of Utah

Deaf Woman hears her own voice for the first time - Video

29 year old Sloan Churman was born deaf. She used to read lips up-till now or used hearing aids to a very limited extent.

Two months ago, she received Envoy Medical's Esteem Implant, which utilizes ear drum vibrations to bring hearing back to its users.

Her husband captured her reaction on video. Her reaction was extraordinary and full of joy.

Why Current In-the-Ear Hearing Aids Fail

Hearing aids have improved greatly over recent years, but they continue to be a surprisingly frustrating experience for new wearers.

Clearly, today’s hearing aids are tiny, nearly invisible in fact, and they amplify sound and are able to present a higher range of frequencies, but they have not yet completely solved the problem of amplifying the peripheral sounds we just don’t want, or don't need to hear.

For new wearers the crumpling of a paper bag on the other side of a room can sound like a jackhammer.

This is a huge challenge for technology because it is dependent on how the brain perceives sound and how we have learned to filter peripheral sound out of normal hearing. Andrew J. Oxenham is a psychologist and hearing expert at the University of Minnesota and an expert in psychoacoustics.

Oxenham explains: The ear works by analysing sound and breaking it into different frequencies and with many forms of hearing impairment it’s this frequency selectivity that is impaired.

What that means is that the ear doesn’t filter as well as it did before. So instead of having very sharp tuning to filter out different frequencies the filtering becomes much broader and there is no real way of compensating for that.

You can’t sharpen the filters or you can’t pre-process sound so it’s sharp. It’s like a broken TV set. You can process the signal going into the TV as much as you like but you still won’t get a clear picture of the output.

Recent hearing aids have made a lot of progress, like being able to present frequencies of up to 6000 Hz as opposed to limited frequencies up to about 4000 Hz, by using digital signal processing, and a lot more computing power on a lot smaller chip.

Another big leap forward has been made with directional hearing. They can focus the microphones toward the front and filter out a lot of the sound coming from the side and back. And although that is a fairly simple technique, it involves signal processing that wasn’t possible with earlier hearing aids.

Ambient or peripheral sound is horribly distracting for hearing aid wearers. A paper bag being crumpled across a room sounds screechingly loud.

This is common complaint of people who recently start wearing a hearing aid. Their hearing has deteriorated, often without them being completely aware of it, over a period of time.

When they are suddenly fitted with a hearing aid, they hear sounds they’ve got used to not hearing. The sounds are suddenly annoying and distracting. It’s a contrast effect.

It’s more to do with perception i.e the brain’s ability to analyse and prioritise different sounds.

It’s a complex interaction between the ear and the brain. The ear sends signals up to the brain; the brain does an awful lot of processing on top of that; then sends signals back down to the ear. These signals change the way the ear accepts input.

This is partly why hearing aids are not perfect because the hearing aid is not part of that natural feedback loop. There’s no way with current aids that the brain can interface with a hearing aid directly to change its characteristics.

Hearing Loops
To deal with background noise there are things called “hearing loops.”

These are systems that are set up within places like concert halls and churches that interface directly with the hearing aid. It’s like sending a radio signal to the hearing device.

The idea is that this hearing loop picks up the sound directly from the microphone in front of a speaker.

If you are in a conference and the speaker is talking into a microphone. Normally we hear the sound acoustically through the airwaves.

If you are wearing a regular hearing aid the microphone will pick up the sounds on the airwaves but that is together with all the background noise and reverberation in the room.

With a hearing loop it sends the signal directly from the microphone to the ear and bypasses all the acoustics in the building itself. So the ear is getting a much better, clearer and cleaner signal of what’s coming into the microphone.

Two hearing aids better than One?
It’s only recently that people have routinely been fitted with two hearing aids. Often people only got one.

Directional hearing and the way we localise sound: To know where the sound is coming from the brain compares the signals coming into the two ears. So if it’s slightly louder on one side then the brain knows the sound is coming from that side.

More importantly it’s the time of arrival difference between the two ears. If you think about a sound coming from the right. The sound will reach your right ear a little bit before it reaches your left ear.

Although we are talking about millionths of seconds, your brain needs two ears to make a distinction. If you only have one you lose that ability to localise sound and tell which direction it is coming from.

It’s also an important part of filtering out sound and noise. The brain can determine if there is speech right in front and background noise in back of and to the side. The brain can use those differences in localisation to help to make the speech more intelligible.

So the biggest technical challenge is developing hearing aids that can focus on what we really need and want to listen to. This is the current problem.

The Solution
We are hoping through even more sophisticated signal processing schemes that we’ll be able to work on artificial source segregation; i.e. analysing the signal that is coming in and figuring out what is speech and what isn’t, and only presenting to the ear the wanted signal.

Distinguishing between speech and noise
The assumption is that what you really want to listen to is speech, and so there are certain acoustical aspects of speech that we can recognise and there are certain acoustical aspects of noise that are different from speech.

So, we need to establish a suitable algorithm to be able to distinguish between speech and noise that will help you towards filtering the unwanted signal.

A more complete solutiion could mean that brain-computer interface may be part of the hearing aid systems of the future. Where the hearing aid is tapping into brain responses to pick up the specific signal the person wants to pay attention to.

This is an ongoing process with incremental steps and we will continue to see improvements over the next 15 years.

Research discovers how the deaf have super vision

Deaf or blind people often report enhanced abilities in their remaining senses, but up until now, no one has explained how and why that could be.

Researchers at The University of Western Ontario, led by Stephen Lomber of The Centre for Brain and Mind have discovered there is a causal link between enhanced visual abilities and reorganisation of the part of the brain that usually handles auditory input in congenitally deaf cats.

The findings, published online in Nature Neuroscience, provide insight into the plasticity that may occur in the brains of deaf people.

Cats are the only animal besides humans that can be born deaf. Using congenitally deaf cats and hearing cats, Lomber and his team showed that only two specific visual abilities are enhanced in the deaf: visual localisation in the peripheral field and visual motion detection.

They found the part of the auditory cortex that would normally pick up peripheral sound enhanced peripheral vision, leading the researchers to conclude the function stays the same but switches from auditory to visual.

“The brain is very efficient, and doesn’t let unused space go to waste,” says Lomber, an associate professor in the Department of Physiology and Pharmacology at the Schulich School of Medicine & Dentistry, and Department of Psychology in the Faculty of Social Science.

“The brain wants to compensate for the lost sense with enhancements that are beneficial. For example, if you’re deaf, you would benefit by seeing a car coming far off in your peripheral vision, because you can’t hear that car approaching from the side; the same with being able to more accurately detect how fast something is moving.”

Lomber and his team are trying to discover how a deaf brain differs from a hearing brain to better understand how the brain handles cochlear implants. If the brain has rewired itself to compensate for the loss of hearing, what happens when hearing is restored?

“The analogy I use is, if you weren’t using your cottage and lent it to a friend. That friend gets comfortable, maybe rearranges the furniture, and settles in. They may not want to leave just because you’ve come back,” explains Lomber.

He also plans to conduct research to see if these changes in the brain also happen to those who could hear at one time, or if auditory experience prevents the changes from occurring.

Baby Hears his Mother's Voice for the First Time

For the first eight months of his life, baby Jonathan had never heard the sound of his mom’s voice, but a cochlear implant changed all that. Jonathan’s dad captured the touching moment on video: