Category: Tinnitus

On the battlefield, a soldier's hearing can be permanently damaged in an instant by the boom of an explosion, and thousands of soldiers returning from Iraq have some permanent hearing loss. But what if soldiers could take a pill before going on duty that would prevent damage to hearing?

Research at Washington University School of Medicine in St. Louis suggests a medicinal form of hearing protection may someday be a possibility. A group headed by Jianxin Bao, Ph.D., research associate professor of otolaryngology and head of the Central Institute for the Deaf's Presbycusis and Aging Laboratory, has found that two anti-epileptic drugs can prevent permanent hearing loss to a significant degree in mice exposed to loud noises.

"The military has a tremendous need for preventing noise-induced hearing loss," Bao says. "But others would also benefit. For example, many hunters have hearing loss on the side where they hold their gun, and pilots are especially prone to hearing loss because of the noise in airplane cabins. Protective equipment or earplugs aren't always appropriate, and right now no drug on the market can prevent or treat noise-induced hearing loss."

Bao's laboratory is dedicated to the study of both age-related and noise-induced hearing loss. About 28 million Americans have a hearing impairment, and excessive noise is the predominant cause of permanent hearing loss. At least 30 million people in the United States encounter hazardous levels of noise at work, particularly in jobs such as construction, mining, agriculture, manufacturing, transportation and the military.

Bao and colleagues found that if they exposed mice to loud sounds and then gave them trimethadione (Tridione®) or ethosuximide (Zarontin®) — anticonvulsive medications used to treat epilepsy — they could prevent a significant amount of permanent hearing loss. When mice got the medications before noise exposure, only trimethadione, not ethosuximide, significantly reduced subsequent hearing loss. The results are reported in Hearing Research and are now available through advanced online publication.

Bao notes that other researchers are investigating agents such as antioxidants for their potential in preventing hearing loss, but the two anticonvulsive drugs his lab studied have had FDA approval and so could be used much sooner in clinical trials that study hearing loss.

The experiments in mice showed that the drugs could reduce by about five decibels the permanent threshold shift that can occur after noise exposure. For example, if the softest sound the mice could hear before the noise was 30 decibels, after the noise it might take a louder, 50-decibel sound for the untreated mice to hear but only 45 decibels for the treated mice. A decibel is a standard unit of sound, and normal conversation is around 60 decibels.

"In people, a five decibel difference in hearing ability can be important for everyday speech," Bao says. "We will continue our investigations of these kinds of drugs to see if we can improve the results. One possibility is to combine an anticonvulsant with an antioxidant to increase the protective effect."

Both drugs tested are T-type calcium channel blockers, which inhibit the movement of calcium ions into nerve cells. In the ear, calcium may play a role in causing damage to hair cells (specialized cells that sense sound vibrations) and the nerve cells that connect the hair cells to the hearing centers of the brain.

These anti-epileptic drugs can have unwanted side effects such as dizziness and sleepiness. "The drugs' side effects would be detrimental in certain situations," Bao says. "But lowering the dosage and combining them with other drugs may be effective. Newer versions of anti-epilepsy drugs have fewer side effects, and it may be possible to modify the structure of the drugs so that they don't cross into the brain, which could avert some side effects."

Shen H, Zhang B, Shin J-H, Lei D, Du Y, Gao X, Wang Q, Ohlemiller KK, Piccirillo J, Bao J. Prophylactic and therapeutic functions of T-type calcium blockers against noise-induced hearing loss. Hearing Research Dec 31, 2006 (advanced online publication).

Funding from the National Institutes of Health and the National Organization for Hearing Research Foundation supported this research.

Have you ever walked by someone listening to their i-Pod loud enough for you recognize the song? Studies have shown noise-induced hearing loss is going to become the next big epidemic affecting our younger generation though the effects won't show until it is too late to treat.

In addition to loud noise, certain cancer drugs or genetic factors can cause hearing loss in humans due to loss or faulty development of the sensory 'microphones' (hair cells) inside the ear — the cochlea. Lost hair cells are not replaced and people exposed to these conditions face permanent hearing loss. Identification of the stem cells from the adult cochlea would be a major step forward to develop new therapeutic approaches to hearing loss.

Members of the National Center for Regenerative Medicine research team, Dr. Robert Miller and Dr. Kumar Alagramam, both of Case Western Reserve University School of Medicine, recently published research findings in Developmental Neuroscience which suggest new ways of treating hearing loss. These researchers have isolated "cochlear stem cells" located in the inner ear and already primed for development into ear-related tissue due to their proximity to the ear and expression of certain genes necessary for the development of hearing. "Previous work in our lab with young-adult mouse cochlear tissue showed expression of genes normally found in stem cells and neural progenitors. This led us to hypothesize that cochlea harbors stem cells and neural precursor cells. Our work in collaboration with Miller's lab supports our hypothesis" Dr. Alagramam said.

They say that in early life, these precursor cells may be able to regenerate hair cells, but their capacity to do so becomes limited as the ear develops and ages. The team's research is a major step in devising a therapy to reverse permanent hearing loss because it may lead to the activation of cochlear stem cells in the inner ear to regenerate new hair cells. "Clearly we have miles to go before we reach our end goal, but the exciting part is now we can test compounds that could promote regeneration of hair cells from these precursor cells in vitro, we can study the genes expressed during the transition from stem cells to hair cells, and we can think of developing strategies for cell replacement, i.e. transplanting these cochlear stem cells into the adult cochlea to affect hair cell replacement in the mouse, by extension, in humans" remarked Dr. Alagramam.

In this paper, Drs. Miller and Alagramam offer further evidence for the existence of cochlear stem cells in the mouse cochlea by confirming the ability to form 'stem cell' spheres in culture and by characterizing these cells in terms of neural and hair cell development using a panel of stem cell development and hair cell markers. The formation of spheres from early postnatal cochlear tissues and their expression of a wide range of developmental markers unique to hair cells confirm the possibility that self-supporting hair cell precursors exist in or can be derived from the postnatal mammalian cochlea.

Currently there are no clinical treatments to repair these hair cells vital to normal hearing. In the United States, 30% of people over the age of 65 have a handicapping hearing loss and of those, one in 500 people become deaf before reaching adulthood. In most cases, the target is the highly specialized hair cells.

Docked inside the spiral duct of the human cochlea are ~15,000 hair cells, which are highly specialized neuroepithelial cells that enable us to hear a violin or a whisper. These hair cells differ in length by minuscule amounts and are set in motion by specific frequencies of sound. We hear this sound because this motion induces the hair cell to release an electrical impulse which passes along the auditory nerve to the brain. If the sound is too loud, the hair cells are damaged and no longer send signals to the brain. Severely damaged hair cells do not repair themselves nor do they regenerate naturally.

While further research is necessary, the researchers believe these precursor cells have the potential to regenerate the damaged hair cells and restore normal hearing. The team has already begun animal studies to explore the use of cochlear stem cells in well-established hair cell ablation models and in deaf mouse mutants with predictable patterns of early hair cell loss. This line of research will evaluate the in vivo survival and differentiation of self-renewing cochlear cell populations and potentially lead to new therapies for the numerous individuals that are going to suffer from noise-induced hearing loss in the near future.

— It is estimated that between 10 and 17% of the population has suffered tinnitus at some time in their lives, according to a number of international studies. Tinnitus is understood as the perception of noise in the ears or inside the head although there is no external source of sound, without any vibratory cochlear activity taking place (which occurs when an external noise is produced). Depending on the intensity of the symptom, the patient may have their everyday life affected. In extreme cases the discomforts may make working routines impossible or negatively affect normal daily life.

Doctor Heitzmann has recommended TRT (Tinnitus Retraining Therapy) treatment – based on the neurophysiological model – for those suffering from tinnitus. She points out that it is a treatment the aim of which is to get the patient to become accustomed to the “noise”. To achieve this, therapeutic advice and sound therapy are used.

The father of TRT is professor Pawel J. Jastreboff, who has defined tinnitus as a phantom auditory perception perceived only by the person. On applying the neurophysiological model in the University Hospital (of Navarre), Ms Heitzmann concluded that getting used to the tinnitus and thereby, achieving the cessation of discomfort, occurred in between 80 and 84% of patients, including, at times, a higher proportion. It is the treatment that has the highest success rate currently.

Other therapeutic methods, such as pharmacological ones, help to control the effects produced by tinnitus, such as anxiety and stress, but do not solve the problem, itself. Surgical operations have also shown to be of limited application for this disorder.

Various origins

Tinnitus may be triggered by various factors: from a wax plug in the ear or infection in the middle ear, to hearing loss or a benign tumour. Nevertheless, the origin of the problem mostly lies in the ear itself and in the internal auditory passage.

Nevertheless, knowing the possible origin of the tinnitus has not often been helpful in identifying its treatment. Ear specialists must always undertake a diagnosis. But, in the case of tinnitus, the diagnosis is more often than not one of exclusion. The specialist has to discard other pathologies in order to discern if the noises come from the ear itself or not.

On occasions, tinnituss appear accompanied by other manifestations that oblige the intervention of various medical specialists in order to contribute to relieving this symptom. This is why TRT treatment is applied in the most appropriate way in those medical centres equipped for all specialities; in this way, a multidisciplinary treatment of the patient is achieved.

Getting used to noise

With the application of the TRT neurophysiological model, what is important to know about the tinnitus is the manner in which the noise is made, from the peripheral organ (the ear) to the cerebral cortex. There is a series of structures in the central nervous system (CNS) that gives the tinnitus a magnified role. This fact alerts the patient and turn triggers the perception of auditory discomfort, according to Ms Heitzmann. The limbic system, responsible for emotions and learning, is then activated and the autonomous nervous system, which causes the discomfort. It is at these levels that intervention can take place.

This is why the approach proposed by Jastreboff and which we apply at the University Hospital is based on getting the patient to become used to the noise to the point where the tinnitus ceases to be a nuisance.

In this sense, the specialist believes that the disappearance of the tinnitus in itself is not the important thing, given that, on many occasions, we cannot avoid the ear hearing a noise or the auditory canal transmitting it. Dr Heitzmann points out that when we speak of “getting accustomed” to something, we mean ceasing to be conscious of the presence of a stimulus, something which is achieved if we learn to consider it irrelevant or not to take any notice of it.

It is something similar to the clothes we wear – normally we are not constantly aware of what we have on and it does not bother us. So, getting used to the noise is synonymous with ceasing to be conscious of the tinnitus when one does not take any notice of it. Or, when notice is taken of it, and so the tinnitus is perceived, it does not cause discomfort or annoyance and is quickly forgotten.

Doctor Heitzmann considers that perceiving a tinnitus does not mean anything of significance, once diagnosed and when it does not present a vital risk to the patient and he or she does not need any other treatment. This is confirmed by the fact that there are many who are aware of tinnitus, but are not at all bothered by them. The well-known experiment by Heller and Bergman in 1953 had already shown that all of us perceive tinnitus in specific situations with no obvious illness involved and, so, in principle, it is a symptom that is frequent and irrelevant.

Therapeutic Advice and Sound Therapy

In working on TRT, Jastreboff showed that the central nervous system (CNS) has an elasticity and capacity for learning. The fact the tinnitus generates annoyance means that the CNS processes it as an important sound. We can teach the system to stop processing it at this level of importance and leave it at a subconscious level. This goal is achieved in two ways: therapeutic advice and sound therapy, fundamental tools in TRT.

Through therapeutic advice, the specialist gives the patient an explanation of what is happening and the cause of the discomfort being triggered, always after undertaking an assessment using questionnaires and clinical records, together with an auditory examination and study and, if deemed necessary, with complementary tests. An overall evaluation of the patient is essential.

The aim of therapeutic advice is to help to minimise the importance of the tinnitus. It involves eliminating the negative significance that makes the sound pass to a conscious level in the patient and cause discomfort. In this way, “disconnecting” the limbic system is achieved and the negative emotion or reaction is eliminated little by little.

Therapeutic advice is carried out over a number of interviews between the specialist and patient. Doctor Heitzmann underlines the importance of these sessions, pointing out that, without these interviews, sound therapy will not produce results.

The second TRT tool, sound therapy, arose from the discovery that, depriving the auditory passage, designed for hearing, of sound, tends to increase the sensitivity of the ear. In such a way that, when a sound – such as a tinnitus – is produced in the passage, it captures it straight away. To avoid this phenomenon, external sound is introduced into the auditory canal, thus reducing the perception of the tinnitus at a cortical level (in order to be less conscious of what there is and distract attention away from the tinnitus by means of this external sound).

Sound therapy, thus aims at helping the patient to get used to the tinnitus, by incorporating external sound in such a way that silence is always avoided. It has various levels of application. On the one hand, all patients are advised to avoid silence at all times, using this external source of sounds. Moreover, some patients require sound generators that emit white (neutral) sound and that have to be inserted in the ears for 8 hours a day, the noise never masking the tinnitus. Other patients with auditory loss need an adaptaiton to the headphones. The application of the therapy must always adapt to the circumstances and needs of each person.

The time estimated in getting the patient accustomed to the tinnitus and the disappearance of the discomfort depends on a number of factors, such as how long the tinnitus has taken to evolve, the psychological profile of the patient, personal circumstances that and other pathologies. All these factors can contribute to the getting used to the acufeno being achieved within a year, a year and a half or two years (the average estimated period) although these times may be longer, due to the factors mentioned. Not achieving the target in this time is thus not considered a failure. To help in the process, monitoring is required involving 5-6 clinical visits over 2 years, although this can vary according to the individual.

Surgery to remove tumors under the brain known as acoustic neuromas produces favorable outcomes in the "vast majority" of patients, according to one of the largest studies of its kind.

Loyola University Hospital surgeons Dr. Douglas Anderson and Dr. John Leonetti followed 730 patients whom they had jointly operated on during a 21-year period. Patients ranged in age from 9 to 79, with a median age of 48. The average clinical follow-up was 32 months.

Every patient survived the surgery, and the surgeons were able to completely remove the tumors in 95.1 percent of the patients. Ninety percent of patients experienced little or no facial paralysis. And among those who still retained hearing in the affected ear before surgery, 44 percent came out of the surgery with useful hearing in that ear, and 63 percent had at least some hearing.

These results are as good as or better than any other series of acoustic neuromas reported in the medical literature.

"With careful microsurgical technique, one can achieve gross total resection [removal] of the vast majority of acoustic tumors with minimal major morbidity or mortality and at the same time achieve a high percentage of normal to near-normal facial function," the study authors concluded.

Anderson is first author of the study. He presented results at the 2010 Congress of Neurological Surgeons, which awarded him the Synthes Skull Base Surgery Award.

An acoustic neuroma, also known as a vestibular schwannoma, is a slow-growing, usually benign, tumor, located behind the ear on the nerve that connects the ear to the brain. The tumor can cause hearing loss in one ear and paralysis on one side of the face. If the tumor grows large enough, it can be fatal. Treatment options include microsurgery (surgery with a microscope), radiation or simply keeping a watchful eye on the tumor.

In the study, the average tumor diameter was 2.2 cm, and 89.5 percent of patients had experienced partial or complete loss of hearing in one ear. Other presurgery symptoms included tinnitus (43.7 percent of patients), dizziness/imbalance (26.8 percent), facial numbness (11.1 percent), headache (10.3 percent) and facial weakness (2.6 percent).

Leonetti and Anderson work as a team, with Leonetti gaining access to the tumor and Anderson removing it. If the patient still retains hearing, Leonetti uses one of two surgical techniques, called the retrosigmoid approach or the middle fossa approach. If the patient has lost all hearing, Leonetti uses a technique called the translabyrinthine approach. Leonetti is a professor in the departments of Otolaryngology and Neurological Surgery and program director of Cranial Base Surgery, and Anderson is a professor in the Department of Neurological Surgery at Loyola University Chicago Stritch School of Medicine.

In recent years, the adoption of techniques to monitor neural structures during surgery has enabled surgeons to frequently preserve hearing and facial nerves. "Before, the goal simply was to get the tumor out and be glad if the patient survived," Anderson said.

Though Anderson and Leonetti have their own practices, they also collaborate to remove acoustic neuromas and other tumors. Over the last 23 years, they have performed about 1,250 surgeries together.

"It's been a long and successful partnership," Anderson said. "We have had wonderful results. It's like a nice marriage."

Anderson said Leonetti "is a very innovative surgeon, and extremely adept at the myriad of approaches to the skull base. He also has a wonderful attitude — highly professional but also fun to work with."

Leonetti also has high praise for Anderson. "He is the most technically gifted neurosurgeon I have ever seen," Leonetti said. "More importantly, he is a kind, compassionate and wonderful person, but he'll never beat me at golf."

Other co-authors of the study are Dr. Edward Perry, a resident in neurological surgery and Marc Pisansky, a research assistant.

 Research shows that vibrations in the inner ear continue even after a sound has ended, perhaps serving as a kind of mechanical memory of recent sounds. In addition to contributing to the understanding of the complex process of sound perception, the results may shed light on other fascinating aspects of the auditory system, such as why some gaps between sounds are too brief to be perceived by the human ear.

The study is published by Cell Press in the April 5th issue of Biophysical Journal.

The inner ear contains a structure called the cochlea that serves as the organ of hearing. The cochlea is a coiled, fluid filled structure that contains a "basilar" membrane and associated "hair cells." Essentially, sound-evoked vibrations of the basilar membrane are sensed by the hair cells which in turn convey auditory information to the nervous system. Some hair cells respond to basilar membrane vibrations by producing forces that increase hearing sensitivity and frequency selectivity through mechanisms that are not completely understood. "Because hair cell force production is initiated by the acoustic stimulus, it was assumed to end when the stimulus was removed," says senior study author, Dr. Alfred L. Nuttall from the Oregon Hearing Research Center. "However, there is evidence that some tones produce vibrations that continue even after the end of the stimulus."

Using anaesthetized guinea pigs, Dr. Nuttall and colleagues recorded basilar membrane motion and hair cell related potentials in response to various sounds. They observed that after-vibrations were dependent on the magnitude and frequency of the sound stimuli and that even minor hearing loss elicited a profound reduction in after-vibrations. "The after-vibrations appear to be driven by sustained force production in the inner ear — a form of short-term memory of past stimulations," says Dr. Nuttall. "It is important to point out that although our findings clearly document the existence of after-vibrations, further work is needed to elucidate the underlying mechanism."

The authors also discuss the potential relevance of after-vibrations for sound perception. "The ability to detect brief gaps in an ongoing stimulus is critical for speech recognition; gaps need to be longer than a minimal interval to be perceived," explains Dr. Nutall. "To the extent that after-vibrations excite the auditory nerve fibers, they may explain part of the difficulty in detecting such gaps."

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Journal Reference:

1. Jiefu Zheng, Sripriya Ramamoorthy, Tianying Ren, Wenxuan He, Dingjun Zha, Fangyi Chen, Anna Magnusson, Alfred L. Nuttall, Anders Fridberger. Persistence of Past Stimulations: Storing Sounds within the Inner Ear. Biophysical Journal, 2011; 100 (7): 1627-1634 DOI: 10.1016/j.bpj.2011.02.025

Targeted nerve stimulation could yield a long-term reversal of tinnitus, a debilitating hearing impairment affecting at least 10 percent of senior citizens and up to 40 percent of military veterans, according to an article posted in the Jan. 12 online edition of Nature.

Researchers Dr. Michael Kilgard and Dr. Navzer Engineer from The University of Texas at Dallas and University-affiliated biotechnology firm MicroTransponder report that stimulation of the vagus nerve paired with sounds eliminated tinnitus in rats. A clinical trial in humans is due to begin in the next few months.

Described as a ringing in the ears, tinnitus causes mild irritation for some people but is disabling and painful for many others. The U.S. Veterans Administration spends about $1 billion a year on disability payments for tinnitus, said Kilgard, associate professor in the School of Behavioral and Brain Sciences at UT Dallas and co-author of the journal article.

Tinnitus is a symptom some people experience as a result of hearing loss. When sensory cells in the inner ear are damaged, such as from loud noise, the resulting hearing loss changes some of the signals sent from the ear to the brain. For reasons that are not fully understood, some people will develop tinnitus as a result.

"We believe the part of the brain that processes sounds—the auditory cortex—delegates too many neurons to some frequencies, and things begin to go awry," said Michael Kilgard, Ph.D., associate professor of behavior and brain sciences at UT-Dallas, and a co-principal investigator on the study. "Because there are too many neurons processing the same frequencies, they are firing much stronger than they should be."

In addition, the neurons fire in sync with one another and they also fire more frequently when it is quiet. According to Dr. Kilgard, it's these changing brain patterns that produce tinnitus, which is usually a high-pitched tone in one or both ears, but it may also be heard as clicking, roaring, or a whooshing sound.

"Brain changes in response to nerve damage or cochlear trauma cause irregular neural activity believed to be responsible for many types of chronic pain and tinnitus," he said. "But when we paired tones with brief pulses of vagus nerve stimulation, we eliminated the physiological and behavioral symptoms of tinnitus in noise-exposed rats."

The researchers are, in essence, retraining the brain to ignore the nerve signals that simulate ringing. They monitored the laboratory rats for several weeks after therapy, and the improvements persisted.

"This minimally invasive method of generating neural plasticity allows us to precisely manipulate brain circuits, which cannot be achieved with drugs," said Dr. Navzer Engineer, vice president of preclinical affairs at MicroTransponder and lead author on the study. "Pairing sounds with VNS provides that precision by rewiring damaged circuits and reversing the abnormal activity that generates the phantom sound."

The research team is developing parameters for a clinical trial in humans. Vagus nerve stimulation (VNS) is currently used in humans for treatment of epilepsy and depression. "The translation from basic science to the clinic has been quite rapid," Engineer said. "It's exciting that the National Institutes for Health has been so supportive of our efforts to move this work along faster, in hopes of providing effective treatments to tinnitus patients."

The National Institutes of Health (NIH) early in 2010 granted Kilgard and MicroTransponder $1.7 million to further investigate whether nerve stimulation offers a long-term cure for tinnitus.

The first patient could be treated in Europe by early 2011, Engineer said. The initial set of human participants will have the electrodes attached to the left vagus nerve in their neck during a short outpatient procedure. They will come to the clinic Monday through Friday for a few weeks of treatment. At each daily session, they will experience VNS paired with sounds.

MicroTransponder, a neuroscience based medical device company, was founded by UT Dallas PhD candidate Will Rosellini and sponsored by the school's Institute for Innovation and Entrepreneurship. MicroTransponder is developing a less invasive wireless medical device to stimulate the vagus nerve. The UT Dallas/MicroTransponder team also is studying how best to optimize the paired therapy for tinnitus patients.

Past research has shown that the severity of chronic pain and tinnitus is tied to the degree of plasticity in the brain's cortex. A previous study showed that repeatedly pairing sensory stimuli with electrical stimulation of a brain structure called nucleus basalis generates powerful and long-lasting changes in cortical organization. Since the vagus nerve is easier to access for clinical use, and is known to trigger the release of molecules in the brain that promote neural changes, follow-up studies were performed on the vagus nerve.

For the VNS study, the research team used a "gap detection model" to document tinnitus in rats that were exposed to loud noise for one hour while under anesthesia. Each of the noise-exposed rats used in this study exhibited a significant impairment in the ability to detect a quiet gap in a tone near their tinnitus frequency, but exhibited no impairment when the gap was placed in a higher or lower tone.

"Previous research showed that a frequency-specific impairment in gap detection is a likely sign that noise-exposed rats experience a mid-frequency tinnitus 'ringing' that fills the silent gaps," Kilgard said. "Though it isn't possible to evaluate the subjective experience of rats, this gap impairment has been taken as an indicator of tinnitus."

When the rats were exposed to VNS paired with sounds, the gap impairment was eliminated — indicating that the tinnitus was gone.

Today's therapies for tinnitus have limited success and frequently must be modified over time because they become ineffective. "The VNS treatment would be an improvement over current therapies involving medications or counseling because it offers a possible permanent end to the condition and doesn't appear to cause any significant side effects," Kilgard said.

Additional sponsors of the work include the James S. McDonnell Foundation, the Norman Hackerman Advanced Research Program and the Texas Emerging Technology Fund.

The paper's other authors were: UT Dallas neuroscientists Drs. Jonathan Riley, Jonathan Seale, Will Vrana, Jai Shetake, Sindhu Sudanagunta and Michael Borland. The article will be published in the Jan. 27 print edition of the journal.

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Journal Reference:

1. Navzer D. Engineer, Jonathan R. Riley, Jonathan D. Seale, Will A. Vrana, Jai A. Shetake, Sindhu P. Sudanagunta, Michael S. Borland, Michael P. Kilgard. Reversing pathological neural activity using targeted plasticity. Nature, 2011; DOI: 10.1038/nature09656

— Tinnitus appears to be produced by an unfortunate confluence of structural and functional changes in the brain, say neuroscientists at Georgetown University Medical Center (GUMC).

The phantom ringing sounds heard by about 40 million people in the U.S. today are caused by brains that try, but fail to protect their human hosts against overwhelming auditory stimuli, the researchers say in the January 13th issue of Neuron. They add that the same process may be responsible for chronic pain and other perceptual disorders.

The researchers say that the absence of sound caused by hearing loss in certain frequencies, due to normal aging, loud-noise exposure, or to an accident, forces the brain to produce sounds to replace what is now missing. But when the brain's limbic system, which is involved in processing emotions and other functions, fails to stop these sounds from reaching conscious auditory processing, tinnitus results.

"We believe that a dysregulation of the limbic and auditory networks may be at the heart of chronic tinnitus," says the study's lead investigator, Josef P. Rauschecker, PhD, a neuroscientist. "A complete understanding and ultimate cure of tinnitus may depend on a detailed understanding of the nature and basis of this dysregulation."

Tinnitus isn't curable, although antidepressants appear to help some patients, as does the use of masking noise to diminish focus on the ringing sensations.

Using functional Magnetic Resonance Imaging (fMRI), the Georgetown researchers tested 22 volunteers, half of whom had been diagnosed with chronic tinnitus. They found that moderate hyperactivity was present in the primary and posterior auditory cortices of tinnitus patients, but that the nucleus accumbens exhibited the greatest degree of hyperactivity, specifically to sounds that were matched to frequencies lost in patients.

The nucleus accumbens is part of the corticostriatal circuit, which is involved in evaluation of reward, emotion, and aversiveness, says Rauschecker. "This suggests that the corticostriatal circuit is part of a general 'appraisal network' determining which sensations are important, and ultimately affecting how or whether those sensations are experienced," he says. "In this study, we provide evidence that these limbic structures, specifically the nucleus accumbens and the ventromedial prefrontal cortex, do indeed differ in the brains of individuals with tinnitus."

Functional lapses in these same areas have also been implicated to altered mood states and to chronic pain. "Both of these conditions may also involve the inability to suppress unwanted sensory signals," Rauschecker says.

Based on their findings, the researchers argue that the key to understanding tinnitus lies in understanding how the auditory and limbic systems interact to influence perception — be it sound, emotions, pain, etc.

Grant support was provided by the National Institute on Deafness and Other Communication Disorders, the Tinnitus Research Consortium, the Tinnitus Research Initiative, and the Skirball Foundation.

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Journal Reference:

1. Amber M. Leaver, Laurent Renier, Mark A. Chevillet, Susan Morgan, Hung J. Kim and Josef P. Rauschecker. Dysregulation of Limbic and Auditory Networks in Tinnitus. Neuron, Volume 69, Issue 1, 13 January 2011, Pages 33-43 DOI: 10.1016/j.neuron.2010.12.002

Driving convertible cars with the top open at speeds exceeding 88.5 kilometres per hour (55 miles per hour) may put drivers at increased risk of noise-induced hearing loss, according to new research published in The Journal of Laryngology and Otology, by Cambridge University Press on behalf of JLO (1984) Ltd from the Saint Louis University School of Medicine, Missouri and The Ear Institute of Texas, San Antonio.

The research was carried out using five different makes and models of car. Sound level measurements in 80 per cent of the cars at 88.5 kmph with the top down had maximum sound recordings greater than 85 decibels. Exposure of noise above 85 dB for prolonged periods is not recommended according to the US-based National Institute of Occupational Safety and Health. The higher the noise level, the shorter the recommended exposure time.

At 120.7 kmph (75 mph) the mean noise exposure inflicted on the driver of a convertible car driven with the top open was 89.9 decibels. Not only was the mean noise exposure excessive with the top open, but the driver was also exposed to extreme noise 'spikes' while driving on the highway; for example, when driving next to a motorcycle or lorry. The study was undertaken using a sound level meter operated by a passenger in each car tested. The passenger took a series of between eight to ten sound level measurements at various points in the journey from the position of the driver's left ear, at various speeds. During all data collection, the car radio was turned off, there was no conversation between occupants, air conditioning was turned off, the car horn was not used and there was no rain or other inclement weather.

Drivers of convertible cars may also be exposed to additional noise when listening to the car radio. Even for comfortable listening, the radio volume levels required while driving under the conditions assessed in this study are likely to add significantly to the noise exposure level.

During the study, no excessive noise levels were recorded from any tested car driven with the top closed, meaning there is no more than minimal risk of excessive noise exposure when driving with the convertible top closed.

Dr A A Mikulec from the Saint Louis University School of Medicine, who oversaw the study, said: "When the convertible automobiles were driven with the top open, high levels of noise were consistently recorded. Although driving for short distances under such levels of noise exposure is unlikely to cause a significant degree of noise-induced hearing loss, our study demonstrates that long duration driving at high speeds with the convertible top open will increase the driver's risk of hearing damage."

"In light of the results of this study, we are recommending that drivers be advised to drive with the top closed when travelling for extended periods of time at speeds exceeding 85.3 kmph."

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Journal Reference:

1. A A Mikulec, S B Lukens, L E Jackson, M N Deyoung. Noise exposure in convertible automobiles. The Journal of Laryngology & Otology, 2010; 1 DOI: 10.1017/S0022215110002355

Surgery to remove tumors under the brain known as acoustic neuromas produces favorable outcomes in the "vast majority" of patients, according to one of the largest studies of its kind.

Loyola University Hospital surgeons Dr. Douglas Anderson and Dr. John Leonetti followed 730 patients whom they had jointly operated on during a 21-year period. Patients ranged in age from 9 to 79, with a median age of 48. The average clinical follow-up was 32 months.

Every patient survived the surgery, and the surgeons were able to completely remove the tumors in 95.1 percent of the patients. Ninety percent of patients experienced little or no facial paralysis. And among those who still retained hearing in the affected ear before surgery, 44 percent came out of the surgery with useful hearing in that ear, and 63 percent had at least some hearing.

These results are as good as or better than any other series of acoustic neuromas reported in the medical literature.

"With careful microsurgical technique, one can achieve gross total resection [removal] of the vast majority of acoustic tumors with minimal major morbidity or mortality and at the same time achieve a high percentage of normal to near-normal facial function," the study authors concluded.

Anderson is first author of the study. He presented results at the 2010 Congress of Neurological Surgeons, which awarded him the Synthes Skull Base Surgery Award.

An acoustic neuroma, also known as a vestibular schwannoma, is a slow-growing, usually benign, tumor, located behind the ear on the nerve that connects the ear to the brain. The tumor can cause hearing loss in one ear and paralysis on one side of the face. If the tumor grows large enough, it can be fatal. Treatment options include microsurgery (surgery with a microscope), radiation or simply keeping a watchful eye on the tumor.

In the study, the average tumor diameter was 2.2 cm, and 89.5 percent of patients had experienced partial or complete loss of hearing in one ear. Other presurgery symptoms included tinnitus (43.7 percent of patients), dizziness/imbalance (26.8 percent), facial numbness (11.1 percent), headache (10.3 percent) and facial weakness (2.6 percent).

Leonetti and Anderson work as a team, with Leonetti gaining access to the tumor and Anderson removing it. If the patient still retains hearing, Leonetti uses one of two surgical techniques, called the retrosigmoid approach or the middle fossa approach. If the patient has lost all hearing, Leonetti uses a technique called the translabyrinthine approach. Leonetti is a professor in the departments of Otolaryngology and Neurological Surgery and program director of Cranial Base Surgery, and Anderson is a professor in the Department of Neurological Surgery at Loyola University Chicago Stritch School of Medicine.

In recent years, the adoption of techniques to monitor neural structures during surgery has enabled surgeons to frequently preserve hearing and facial nerves. "Before, the goal simply was to get the tumor out and be glad if the patient survived," Anderson said.

Though Anderson and Leonetti have their own practices, they also collaborate to remove acoustic neuromas and other tumors. Over the last 23 years, they have performed about 1,250 surgeries together.

"It's been a long and successful partnership," Anderson said. "We have had wonderful results. It's like a nice marriage."

Anderson said Leonetti "is a very innovative surgeon, and extremely adept at the myriad of approaches to the skull base. He also has a wonderful attitude — highly professional but also fun to work with."

Leonetti also has high praise for Anderson. "He is the most technically gifted neurosurgeon I have ever seen," Leonetti said. "More importantly, he is a kind, compassionate and wonderful person, but he'll never beat me at golf."

Other co-authors of the study are Dr. Edward Perry, a resident in neurological surgery and Marc Pisansky, a research assistant.

 Age-related hearing loss (ARHL), one of the four most prevalent chronic conditions in the elderly, is associated with low serum levels of folic acid, according to new research published in the December 2010 issue of Otolaryngology — Head and Neck Surgery.

Hearing loss is a major public health problem globally, with more than 28 million Americans between the ages of 60 and 74 dealing with the loss. Despite the high prevalence of hearing impairment, the biological basis of age-related hearing loss is unknown. In the current study, findings show that low serum levels of folic acid among elderly people are significantly associated with hearing loss in high frequencies.

"Based on our research, age-related hearing loss may be associated with poor micronutrient status. The role of folate in cellular metabolism, the nervous system, and vascular function are important for the auditory system," said study author Akeem Olawale Lasisi, MBChB, FWACS, FMCORL.

The study included face-to-face interviews with 126 elderly Nigerian men and women above 60 years old who had no known medical conditions and had been examined by physicians. The study excluded those who were found to have a history of diabetes, stroke, hypertension, ear diseases, ear infections, ear trauma, ear surgery, or exposure to noise and ototoxic drugs such as aminoglycosides, antibiotics, and diuretics.

The main finding of the study was that low serum levels of folic acid were significantly associated with high-frequency hearing loss in the elderly. In medically underserved populations like that in the study, relatively low levels of vitamin intake can be expected. That suggests a need, say the authors, for continuing study into the role of vitamins in auditory function, particularly in developing countries where malnutrition is rife.

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Journal Reference:

1. Akeem Olawale Lasisi, Fatai A. Fehintola, Oyindamola Bidemi Yusuf. Age-related hearing loss, vitamin B12, and folate in the elderly. Otolaryngology – Head and Neck Surgery, 2010; 143 (6): 826 DOI: 10.1016/j.otohns.2010.08.031