Imaging reveals how brain fails to tune out phantom sounds of tinnitus

Jun 23, 2010

About 40 million people in the U.S. today suffer from tinnitus, an irritating and sometimes debilitating auditory disorder in which a person "hears" sounds, such as ringing, that don't actually exist. There isn't a cure for what has long been a mysterious ailment, but new research suggests there may, someday, be a way to alleviate the sensation of this sound, says a neuroscientist from Georgetown University Medical Center (GUMC).

In a Perspective piece in the June 24 issue of Neuron, Josef P. Rauschecker, PhD, says that should be thought of as a disorder akin to the "phantom pain" felt in an amputated limb.

Tinnitus starts with damage to hair cells in the cochlea of the inner ear. This damage forces neurons in the brain's auditory areas, which normally receive input from that part of the cochlea, to become overactive to fill in the missing sound, he says. That extra, unreal noise is normally inhibited - or tuned out - by a corrective feedback loop from the brain's limbic system to the thalamus, where all sensory information is regulated, before it reaches the , where a person becomes conscious of the senses. But that doesn't happen in tinnitus patients due to compromised brain structures in the limbic system.

"Neurons, trying to compensate for loss of an external signal, fire to produce sound that doesn't exist in tinnitus patients, just like neurons send pain signals to someone who has lost a limb," Rauschecker says. "What both people have in common is that they have lost the feedback loops that stop these signals from reaching consciousness."

Rauschecker says this conclusion, from his research and from other leaders in the field, provides the first testable model of human tinnitus that could provide some new avenues for therapy. "If we can find a way to turn that feedback system back on to eliminate phantom sound, it might be possible one day to take a pill and make tinnitus go away," he says.

Given his innovative work in tinnitus, Rauschecker was invited to write the review, and he collaborated with co-authors Amber Leaver, PhD., a researcher in his laboratory, and Mark Mühlau, a neurologist from the Technische Universität in Munich, Germany.

Tinnitus can be caused by damage to hair cells from a loud noise or from neurotoxicity from medications, he says, but more often than not, it is associated with hearing loss in some frequencies that commonly occurs as people grow older. And given that the world is becoming noisier and the population is aging in the U.S., incidence of tinnitus, which is already the most common auditory disorder in humans, is expected to increase even more, researchers say.

Adding to that increase are the rapidly mounting cases of tinnitus in soldiers due to loud explosions, Rauschecker says. "According to the Veterans Administration, tinnitus and post-traumatic stress disorder are the leading medical complaints," he says.

Research into tinnitus has become much more sophisticated of late, and is changing the common understanding of the disorder, Rauschecker says. "It has long been thought, and still is believed by many today, that tinnitus is a problem only of damaged hair cells in the inner ear, and if those hair cells are restored, tinnitus goes away."

The latest research suggests that while tinnitus may initially arise from such peripheral damage, it becomes a problem in the brain's central auditory pathways, which reorganizes itself in response to that damage, he says.

Recent animal models have corroborated this explanation he says, but have not provided a conclusive answer to the location and nature of these central changes. That has led neuroscientists to employ a whole-brain imaging approach, utilizing neurophysiological and functional imaging studies, to visualize various regions of hyperactivity in the auditory pathways of tinnitus patients.

The model that Rauschecker and his co-authors now propose, is that receptors in the auditory region of the brain that do not any longer perceive sensory input from damaged compensate by firing spontaneously and frequently, producing the initial tinnitus signals.

"Like phantom pain, the firing of central neurons in the brain continues to convey perceptual experiences, even though the corresponding sensory receptor cells have been destroyed," he says. "The brain fills in sensations in response to a deficit of input. Neighboring frequencies become amplified and expand into the vacated frequency range. It also happens to people with a hole in their retina. They don't see the hole because the brain fills in what is missing."

Imaging studies further show hyperactivity not only in auditory pathways of the cortex and thalamus but also in the non-auditory, limbic brain structures that regulate a number of functions including emotion. This limbic activation has been interpreted to reflect the emotional reaction of tinnitus patients to phantom sound, but research has now shown the limbic region normally blocks sound sensations sent from the auditory region that are not real. It does this by feeding sensations of sound that are not real back to a area in the thalamus (the thalamic reticular nucleus) that exerts inhibition on the sensory signals and can thus subtract the errant noise.

"This circuit serves as an active noise-cancelation mechanism - a feedback loop that subtracts sounds that should not be there," says Rauschecker. "But in cases where the limbic regions become dysfunctional, this noise-cancelation breaks down and the tinnitus signal permeates to the auditory cortex, where it enters consciousness."

Researchers have also found evidence that this inhibiting gating mechanism can be switched on and off, which explains why some tinnitus patients have a ringing sensation intermittently.

It remains unclear, however, why some individuals who have hearing loss do not develop tinnitus. Given that some people with tinnitus seem to be more susceptible to other disorders like chronic pain and depression, it could be that they have an independent, systemic vulnerability in one or more neurotransmitter systems in the limbic region," Rauschecker says. "That could explain why drugs that modulate neurotransmitters like serotonin appear to help some people out."

Insomnia is also linked to tinnitus, and not because ringing in the ears keeps patients awake, Rauschecker says. "Insomnia may cause tinnitus, and both may be related to serotonin depletion," he says. "It appears tinnitus is the auditory symptom of an underlying syndrome, which becomes evident in patients who happen to have a hearing loss," he says.

Therefore, identification of the transmitter systems involved in the brain's intrinsic noise cancellation system could open avenues for drug treatment of tinnitus, the authors say.

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User comments : 17

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Bob_Kob
2 / 5 (4) Jun 24, 2010
I'm not sure if anyone else has experienced this, but ive been able to tune out the ringing noise by concentration. Imagining that you're 'pulling' the sound slowly out until it it progressively gets quieter.
Nyloc
1.5 / 5 (2) Jun 24, 2010
I've noticed a direct correlation between problematic tinnitus and lack of sleep. By ensuring I get adequate sleep, I can almost eliminate the annoying "squealing" that plagued me for years. This suggests that there are other factors which have not been explained by the author's theory.
Rectinol
1 / 5 (3) Jun 24, 2010
I suspect we are hearing some background electro-spectrum from all those damn mobiles and airwave clutter ... the 'cure' is 2 think about something else ... inevitable faster than light travel should keep u distracted.
mysticshakra
1.7 / 5 (6) Jun 24, 2010
There is no such thing as tinnitus. Everyone can hear that ringing if they are in a quiet place or wear earplugs. Hearing loss just makes it more noticable because there is less distraction from the environment. If everybody can hear it, it means its a real phenomenon and there is nothing to cure.
JamesThomas
5 / 5 (5) Jun 24, 2010
There is no such thing as tinnitus. Everyone can hear that ringing if they are in a quiet place or wear earplugs. Hearing loss just makes it more noticable because there is less distraction from the environment. If everybody can hear it, it means its a real phenomenon and there is nothing to cure.


Certainly there is a normal amount of phantom noise produced by a healthy system. Cancer cells are also common in everyone, but a healthy system defeats them. To say that there is no problem to cure in those with high degrees of Tinnitus, I feel is void of deeper considerations and lacks compassion for those who suffer. People have been know to commit suicide because of this disease.
jbl
5 / 5 (2) Jun 24, 2010
Interesting research.
1. I'm sure that mysticashakra does not mean to be insensitve and cold, but it is a real condition and I have it. I am not a hypochondriac, have no other illnesses, and have no interest whatsoever in being a 'victim' in life.
2. Bob Kob's comment on concentrating on othe things has "some" merit. After diagnisis, scans, help groups and get rich medication, continuing with life and doing one's best is the only current solution.
3. Mine is 24x7, two high pitched screaming tones and very loud. Came on quite suddenly 5 years ago. With sereious concentration, some of it can be reduced. Crowds, traffic, and higher noise conditions aggravate it.
4. Hoping for a treatment/cure, but one must just continue living and ignore the other real background noise in life, such as the misticshakras.
rwigley
not rated yet Jun 24, 2010
Mystic shakra..As someone who has had severe intrusive Tinnitus for 9 years, your flip dismissal of those of us dealing with this debilitating issue shows a profound lack of understanding. You are representing one of the biggest problems most of us have. The "people" who say..."oh, I have that, I just ignore it" Tell me, could you ignore a vacuum cleaner going on high... sitting on your shoulder 24/7, NO Silence... EVER from now until you die! Depending on the perceived volume... meditation, thinking it away is not an option. Some poor souls have literally ended their lives because of the distress. It interferes with thinking, focus, social life, relationships, emotions, quality of life and is an actual form of torture. Then there are people like you telling us there is no such thing and to ignore it. My tinnitus happened because of a brain tumor. Be careful.... you may have to eat your words. In this world, everyone is just a moment away from walking in our shoes.
artguy
1 / 5 (1) Jun 24, 2010
I have a bit of tinnitis myself, and I've noticed something I've never heard anyone else mention. If I clench my teeth, the noise increases a great deal, maybe 5 fold, and then fades almost immediately. I can repeat this over and over. Has anyone else noticed this?
Nyloc
not rated yet Jun 24, 2010
There is no such thing as tinnitus. Everyone can hear that ringing if they are in a quiet place or wear earplugs. Hearing loss just makes it more noticable because there is less distraction from the environment. If everybody can hear it, it means its a real phenomenon and there is nothing to cure.


You obviously haven't experienced 'problematic' tinnitus. I have noticed that the 'squeal' can sometimes be over 85db. Once I was driving at highway speeds with the window open and noticed that it was louder than the wind noise! I used to be anxious about it until I discovered that I could control it with (enough) sleep. I now calmly accept it, knowing that by morning it may almost vanish.
ricarguy
1 / 5 (1) Jun 24, 2010
artguy, yes the same with me. I think you may be on to something. Tensing my jaw makes it noticeably louder. Several months ago one morning I simply woke up with ringing in my ears and it's been there ever since. My dentist has told me some years past that I show signs of grinding my teeth at night.
Sometimes ringing, sometimes more like "pink" noise, like a hiss. My symptoms tend to be worse (more noticeable) when I wake up in the morning or from a nap. Can't say ringing ever keeps me from sleeping and no noticeable correlation to lack of sleep. If I'm busy I don't notice the ringing much, but always there. I must have a mild case.
Doctors (general practitioners) don't seem to know much about it. They asked me if I was at any loud concerts lately or worked at construction sites...

Interesting to read others experiences (and inexperiences).
Felix_Leon
not rated yet Jun 24, 2010
I've had tinnitus for a few yrs now. I'm tired of reading crap solutions, think it away, ignore it, why don't we come up with some realistic solutions. We as tinnitus suffers have to focus twice as hard, concentrate twice as hard, overall think twice as hard as people with normal hearing. I'm just sayin the truth and it hurts, literally.
Cindy62707
1 / 5 (1) Jun 24, 2010
clenching my teeth changes my sound too. It is always on, really a high pitched hissing whine. Clenching it makes it a little louder for a few seconds then it returns to its normal loud. The only time it ever went away for a few seconds was when the audiologist tried matching the frequency and loudness by me listening in head phones and telling him when he matched it. He was amazed at how high he had to crank up both the frequency and volume to reach my sound. Once he reached it we took off the head phones and for a few seconds I had silence! How GOLDEN those few seconds were. To that person who claims there is no such thing as tinnitus - I am at a loss for words at the lack of human compassion this person has for the torture we all have. To never have silence to enjoy the quiet beauty of nature is like being in a prison with constant torture. One can only hope this person is inflicted with it some day so they can apologize to the rest of us.
Cindy62707
5 / 5 (1) Jun 24, 2010
also forgot to say thank you for a well written article that attempts to explain tinnitus in language that we can understand.

How can we sign up to be study patients for any trial Dr. Rauschecker will be doing?
bottomlesssoul
2 / 5 (1) Jun 27, 2010
I wonder if these failed feedback loops from greedy neurons might be found in other conditions besides phantom limb and tinnitus. Maybe it's something like this behind confabulation.
kevinrtrs
1 / 5 (3) Jun 28, 2010
"That could explain why drugs that modulate neurotransmitters like serotonin appear to help some people out."
Insomnia is also linked to tinnitus, and not because ringing in the ears keeps patients awake, Rauschecker says. "Insomnia may cause tinnitus, and both may be related to serotonin depletion," he says. "It appears tinnitus is the auditory symptom of an underlying syndrome, which becomes evident in patients who happen to have a hearing loss," he says.

There is a strong association between reacting to foodstuff and eventual depression because of a depletion of omega 3 oils. Omega-3 oils are used up when the person suffers prolonged exposure to food or other allergies as a result of the immune system being overactive all the time. The resultant/accompanying anxiety stimulates the prolonged production of cortisol which is the main damaging agent in this case.
So the simple "cure" is more calcium, less reactive food[requires an Ag5(?) test] and more omega-3 supplements.
mysticshakra
1 / 5 (2) Jun 28, 2010
What is called tinnitus is in actuality a spiritual phenomenon. Understanding what it is, is the only way to live with it. The tones can be manipulated through your consciousness. There isn't one ringing, there are thousands. What you are hearing are the frequencies of god, if you will. If you sit down and quiet your mind you can learn to move them around and split them. There is a secret involved here concerning the ability to move dimensionally with your consciousness but it requires much in the way of mental ability.
otto1923
not rated yet Jun 29, 2010
What is called tinnitus is in actuality a spiritual phenomenon. Understanding what it is, is the only way to live with it. The tones can be manipulated through your consciousness. There isn't one ringing, there are thousands. What you are hearing are the frequencies of god, if you will. If you sit down and quiet your mind you can learn to move them around and split them. There is a secret involved here concerning the ability to move dimensionally with your consciousness but it requires much in the way of mental ability.
And I thought I had 1000s of little whirling dervishes in my ears-