Improved Understanding Of How Hearing Works
PDF Researchers funded by the Biotechnology and Biological Sciences Research Council (BBSRC) have gained important new insights into how our sense of hearing works. Their findings promise new avenues for scientists to understand what goes wrong when people experience deafness. Their findings are published in Royal Society Open Biology, a new open access journal.
The team was led by Prof John Wood of UCL (University College London). Professor Wood explains: “As many people will already know, our ears are filled with tiny hair cells that move in response to the pressure of a sound wave. But exactly what happens within cells to turn that movement into an electrical signal that our brains’ can interpret as sound has been puzzling scientists for decades. Our findings have given us some new insights into the puzzle.”
The UCL team found that when mice lack two proteins, called TRPC3 and TRPC6, they experience about an 80% drop in their ability to detect high frequency sounds. Intriguingly, the loss of these two proteins also makes the mice slightly less sensitive to light touch sensations. When the mice that lack these proteins are brushed lightly, a third of the nerve cells which would normally fire remain inactive. This finding suggests an important link between how our bodies sense touch and sound.
Only when both TRPC3 and TRPC6 were absent was the mice’s hearing and sense of touch impaired; the loss of each protein on its own had no behavioural effect on the mice. This suggests that the proteins are only parts of a more complex mechanism used in detecting sound and touch.
Professor Wood continues: “We are still a long way from a complete understanding of touch and hearing but this is a really exciting lead. Our next step is to find out what other proteins are involved in this mechanism and how they all interact. Hopefully then, once we know how the mechanism works in people who can hear, we can understand what goes wrong in people who can’t.”
The two proteins, TRPC3 and TRPC6, seem to be able to make a pressure-sensitive ion channel in some cells but not others. In response to tiny pressures, this channel would allow the flow of electrical signals but seems to require some, as yet uncharacterised, additional factor. This research adds to our knowledge of the potential components required for sound transduction in hair cells and provides us with molecular tools to find other interacting proteins that may play a crucial role in hearing.
Professor Wood received the funding to do this work as part of a Longer and Larger award (LoLa) from BBSRC. These provide leading research teams with the time and resources to tackle major scientific questions.
Professor Douglas Kell, BBSRC Chief Executive, said, “Human biology still holds many secrets and there are big gaps in our understanding of even fundamental processes like touch, pain and hearing. As scientists invent new techniques and technologies we are able to investigate the fundamentals of human biology in exciting new ways. This is crucial because only by deepening our understanding of how our bodies work can we find new ways of helping people when things go wrong.”
Article adapted by Medical News Today from original press release.
Biologists Locate Brain’s Processing Point for Acoustic Signals Essential to Human Communication
ScienceDaily (Mar. 8, 2012) — In both animals and humans, vocal signals used for communication contain a wide array of different sounds that are determined by the vibrational frequencies of vocal cords. For example, the pitch of someone’s voice, and how it changes as they are speaking, depends on a complex series of varying frequencies. Knowing how the brain sorts out these different frequencies — which are called frequency-modulated (FM) sweeps — is believed to be essential to understanding many hearing-related behaviors, like speech. Now, a pair of biologists at the California Institute of Technology (Caltech) has identified how and where the brain processes this type of sound signal.
Their findings are outlined in a paper published in the March 8 issue of the journal Neuron.
Knowing the direction of an FM sweep — if it is rising or falling, for example — and decoding its meaning, is important in every language. The significance of the direction of an FM sweep is most evident in tone languages such as Mandarin Chinese, in which rising or dipping frequencies within a single syllable can change the meaning of a word.
In their paper, the researchers pinpointed the brain region in rats where the task of sorting FM sweeps begins.
“This type of processing is very important for understanding language and speech in humans,” says Guangying Wu, principal investigator of the study and a Broad Senior Research Fellow in Brain Circuitry at Caltech. “There are some people who have deficits in processing this kind of changing frequency; they experience difficulty in reading and learning language, and in perceiving the emotional states of speakers. Our research might help us understand these types of disorders, and may give some clues for future therapeutic designs or designs for prostheses like hearing implants.”
The researchers — including co-author Richard I. Kuo, a research technician in Wu’s laboratory at the time of the study (now a graduate student at the University of Edinburg) — found that the processing of FM sweeps begins in the midbrain, an area located below the cerebral cortex near the center of the brain — which, Wu says, was actually a surprise.
“Some people thought this type of sorting happened in a different region, for example in the auditory nerve or in the brain stem,” says Wu. “Others argued that it might happen in the cortex or thalamus. ”
To acquire high-quality in-vivo measurements in the midbrain, which is located deep within the brain, the team designed a novel technique using two paired — or co-axial — electrodes. Previously, it had been very difficult for scientists to acquire recordings in hard-to-access brain regions such as the midbrain, thalamus, and brain stem, says Wu, who believes the new method will be applicable to a wide range of deep-brain research studies.
In addition to finding the site where FM sweep selectivity begins, the researchers discovered how auditory neurons in the midbrain respond to these frequency changes. Combining physical measurements with computational models confirmed that the recorded neurons were able to selectively respond to FM sweeps based on their directions. For example, some neurons were more sensitive to upward sweeps, while others responded more to downward sweeps.
“Our findings suggest that neural networks in the midbrain can convert from non-selective neurons that process all sounds to direction-selective neurons that help us give meanings to words based on how they are spoken. That’s a very fundamental process,” says Wu.
Wu says he plans to continue this line of research, with an eye — or ear — toward helping people with hearing-related disorders. “We might be able to target this area of the midbrain for treatment in the near future,” he says.
Discovery of Hair-Cell Roots Suggests the Brain Modulates Sound Sensitivity
ScienceDaily (Mar. 8, 2012) — The hair cells of the inner ear have a previously unknown “root” extension that may allow them to communicate with nerve cells and the brain to regulate sensitivity to sound vibrations and head position, researchers at the University of Illinois at Chicago College of Medicine have discovered.
Their finding is reported online in advance of print in the Proceedings of the National Academy of Sciences.
The hair-like structures, called stereocilia, are fairly rigid and are interlinked at their tops by structures called tip-links.
When you move your head, or when a sound vibration enters your ear, motion of fluid in the ear causes the tip-links to get displaced and stretched, opening up ion channels and exciting the cell, which can then relay information to the brain, says Anna Lysakowski, professor of anatomy and cell biology at the UIC College of Medicine and principal investigator on the study.
The stereocilia are rooted in a gel-like cuticle on the top of the cell that is believed to act as a rigid platform, helping the hairs return to their resting position.
Lysakowski and her colleagues were interested in a part of the cell called the striated organelle, which lies underneath this cuticle plate and is believed to be responsible for its stability. Using a high-voltage electron microscope at the National Center for Microscopy and Imaging Research at the University of California, San Diego, Florin Vranceanu, a recent doctoral student in Lysakowski’s UIC lab and first author of the paper, was able to construct a composite picture of the entire top section of the hair cell.
“When I saw the pictures, I was amazed,” said Lysakowski.
Textbooks, she said, describe the roots of the stereocilia ending in the cuticular plate. But the new pictures showed that the roots continue through, make a sharp 110-degree angle, and extend all the way to the membrane at the opposite side of the cell, where they connect with the striated organelle.
For Lysakowski, this suggested a new way to envision how hair cells work. Just as the brain adjusts the sensitivity of retinal cells in the eye to light, it may also modulate the sensitivity of hair cells in the inner ear to sound and head position.
When the eye detects light, there is feedback from the brain to the eye. “If it’s too bright the brain can say, okay, I’ll detect less light — or, it’s not bright enough, let me detect more,” Lysakowski said.
With the striated organelle connecting the rootlets to the cell membrane, it creates the possibility of feedback from the cell to the very detectors that detect motion. Feedback from the brain could alter the tension on the rootlets and their sensitivity to stimuli. The striated organelle may also tip the whole cuticular plate at once to modulate the entire process.
“This may revolutionize the way we think about the hair cells in the inner ear,” Lysakowski said.
The study was supported by the grants from the National Institutes of Deafness and other Communication Disorders, the American Hearing Research Foundation, the National Center for Research Resources, and the 2008 Tallu Rosen Grant in Auditory Science from the National Organization for Hearing Research Foundation.
Graduate student Robstein Chidavaenzi and Steven Price, an electron microscope technologist, also contributed by identifying three of the proteins composing the striated organelle and demonstrating how they arise during development. Guy Perkins, Masako Terada and Mark Ellisman from the National Center for Microscopy and Imaging Research in Biological Systems, University of California, San Diego, also contributed to the study.
Sudden Hearing Loss: AAO-HNSF Clinical Practice Guideline
On March 1, 2012, the American Academy of Otolaryngology-Head and Neck Surgery Foundation published a new Clinical Practice Guideline on Sudden Hearing Loss (SHL). This guideline is published as a supplement to Otolaryngology-Head and Neck Surgery.
A sudden loss of hearing is a frightening symptom that most often prompts urgent medical care. Current diagnosis and treatment plans vary greatly. This guideline provides evidence-based recommendations for the diagnosis, management, and follow-up of adults who present with SHL. Prompt, accurate recognition and management of sudden sensorineural hearing loss (SSNHL), a subset of SHL, may improve hearing recovery and patient quality of life. SSNHL affects 5 to 20 per 100,000 population, with about 4,000 new cases per year in the United States.
The purpose of this guideline is to provide all clinicians who may encounter patients with SHL with evidence-based recommendations for diagnosis, counseling, treatment, and follow-up. By focusing on opportunities for quality improvement, the guideline should improve diagnostic accuracy, facilitate prompt intervention, decrease variations in management, reduce unnecessary tests and imaging procedures, and improve hearing and rehabilitative outcomes for affected patients.
“We are pleased that this guideline provides doctors with a set of evidence-based recommendations for patients who present with sudden hearing loss. This guideline will help advance the care of afflicted patients and result in improved outcomes,” said Robert J. Stachler, MD, Guideline Chair.
Key Points for the AAO-HNSF Clinical Practice Guideline: Sudden Hearing Loss
What is sudden hearing loss and why is it important? Sudden hearing loss (SHL) is a frightening symptom that often prompts an urgent or emergent visit to a physician. The guideline primarily focuses on sudden sensorineural hearing loss (SSNHL) in adult patients (aged 18 and over).
The panel recognized that patients enter the health care system with SHL as a nonspecific, primary complaint. Therefore, the initial recommendations of the guideline deal with efficiently distinguishing SSNHL from other causes of SHL at the time of presentation. Prompt recognition and management of SSNHL may improve hearing recovery and patient quality of life (QOL). SSNHL affects 5 to 20 per 100,000 population, with about 4,000 new cases per year in the United States.
Why is the sudden hearing loss guideline newsworthy? This is the first evidence-based guideline on sudden hearing loss in the United States. The guideline’s recommendations should improve diagnostic accuracy, facilitate prompt intervention, decrease inappropriate variations in management, reduce unnecessary tests and imaging procedures, and improve hearing and rehabilitative outcomes for affected patients.
What is the purpose of the sudden hearing loss guideline? To provide clinicians with evidence-based recommendations for the diagnosis, management, and follow-up of patients who present with SHL. The guideline is intended for all clinicians who diagnose or manage adult patients (18 and over) who present with SHL. The guideline was developed by a multidisciplinary panel representing the fields of otolaryngology, otology, neurotology, neurology, family medicine, emergency medicine, audiology, nurse practitioners, and consumer advocacy groups.
What are the newsworthy points made in the guideline?
Prompt and accurate diagnosis is important:
a. Sensorineural (‘nerve’) hearing loss should be distinguished clinically from conductive (‘mechanical’) hearing loss.
b. Unusual presentations such as bilateral SSNHL, recurrent SSNHL, or focal neurological findings (problem with nerve, spinal cord, or brain function) may represent definable underlying disease and should be managed accordingly.
c. The diagnosis of idiopathic sudden sensorineural hearing loss (ISSNHL), is made when audiometry confirms a 30 decibel hearing loss at three consecutive frequencies and an underlying condition cannot be identified by history and physical exam.
Unnecessary tests and treatments should be avoided:
a. Routine head/brain CT scans, often ordered in the ER setting, are not helpful and expose the patient to ionizing radiation.
b. Routine, non-targeted, laboratory testing is not recommended.
c. The following should not be routinely prescribed: antivirals, thrombolytics, vasodilators, vasoactive substances, or antioxidants to patients with ISSNHL.
Retrocochlear workup should be performed in all patients with ISSNHL, regardless of hearing recovery.
Initial therapy for ISSNHL may include corticosteroids.
a. Corticosteroids may be delivered systemically or via intratympanic application.
b. Hyperbaric oxygen, currently not FDA-approved for this indication, may be offered.
Doctors should offer intratympanic steroid perfusion when patients have incomplete recovery from ISSNHL after failure of initial management.
Follow-up and counseling is important:
a. Doctors should educate patients with ISSNHL about the natural history of the condition, the benefits and risks of medical interventions, and the limitations of existing evidence regarding efficacy.
b. Doctors should obtain follow-up audiometry within six months of diagnosis for patients with ISSNHL.
c. Doctors should counsel patients with incomplete hearing recovery about the possible benefits of amplification and hearing assistive technology and other supportive measures.
Joint Statement on Consumer-Administered Hearing Tests and Direct-to-Consumer Hearing Aid Sales
The Academy of Doctors of Audiology (ADA), American Academy of Audiology (AAA), American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS), the American Speech-Language-Hearing Association (ASHA), and International Hearing Society (IHS) stand together, committed to increasing awareness of the benefits of amplification, and to finding safe and effective solutions that help the 75% of consumers who could benefit from hearing aids but cannot afford to purchase them or have chosen not to use them.
While we appreciate the desire of persons, companies, and organizations to reach more individuals in need of hearing aids, our organizations believe that patients must have access to a comprehensive hearing evaluation performed by a hearing health professional, be appropriately fitted by an individual licensed/registered in the state to dispense hearing aids, and have access to auditory rehabilitation and counseling to ensure appropriate fit and use of the hearing aid device. We urge all persons, companies, and organizations who are interested in assisting patients to work with the hearing health community in ensuring that patients have access to the professional services of all qualified hearing health professionals.
Federal and state laws related to the dispensing of a hearing aid are currently in place to protect and ensure consumer safety. Regulations issued by the Food and Drug Administration require that patients under the age of 18 receive a medical evaluation by a licensed physician prior to the purchasing of a hearing aid from a dispenser. A medical evaluation by a licensed physician is also recommended for adults prior to a hearing aid purchase. Many state laws also recognize the importance of consumer protection and safety by placing restrictions on the dispensing of hearing aids by direct mail and/or the internet.
All of our organizations have both health and efficacy concerns about the use of consumer-administered hearing tests and the direct sale of hearing aids to the consumer without the involvement of a licensed hearing health professional – an audiologist, hearing aid specialist, or otolaryngologist. We encourage our respective members and other hearing health care providers to work collaboratively to ensure patient safety and enhance consumer protections related to the purchase of hearing aids and related devices.
Hearing Innovations Expo 2012
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It was a pleasure to meet Sir Richard Branson at the recent Hearing Innovations Expo in Las Vegas. Such great knowledge and innovations were shared by so many inspiring leaders.
Promising Info For Those With Eardrum Perforations
Revolutionary Surgical Technique For Perforations Of The Eardrum
Article adapted by Medical News Today from original press release.
A revolutionary surgical technique for treating perforations of the tympanic membrane (eardrum) in children and adults has been developed at the Sainte-Justine University Hospital Centre, an affiliate of the Universite de Montreal, by Dr. Issam Saliba. The new technique, which is as effective as traditional surgery and far less expensive, can be performed in 20 minutes at an outpatient clinic during a routine visit to an ENT specialist. The result is a therapeutic treatment that will be much easier for patients and parents, making surgery more readily available and substantially reducing clogged waiting lists.
“In the past five years, I’ve operated on 132 young patients in the outpatient clinic at the Sainte-Justine UHC using this technique, as well as on 286 adults at the University of Montreal Hospital Centre (CHUM) outpatient clinic,” says Dr. Saliba. “Regardless of the size of the perforation, the results are as good as those obtained using traditional techniques, with the incomparable advantage that patients don’t have to lose an entire working day, or 10 days or more off school in the case of children.”
The technique, which Dr. Saliba has designated “HAFGM” (Hyaluronic Acid Fat Graft Myringoplasty), requires only basic materials: a scalpel, forceps, a probe, a small container of hyaluronic acid, a small amount of fat taken from behind the ear and a local anesthetic. The operation, which is performed through the ear canal, allows the body by itself to rebuild the entire tympanic membrane after about two months on average, allowing patients to recover their hearing completely and preventing recurring cases of ear infection (otitis). Because it requires no general anesthetic, operating theatre or hospitalization, the technique makes surgery much more readily available, particularly outside large hospital centres, and at considerably lower cost.
“With the traditional techniques, you have to be on the waiting list for up to a year and a half in order to be operated on. Myringoplasty (reconstruction of the eardrum) using the HAFGM technique reduces waiting times, cost of the procedure and time lost by parents and children. What’s more, it will help clear the backlogs on waiting lists,” Dr. Saliba says.
Perforations of the eardrum
Myringoplasty is surgical procedures to repair the tympanic membrane or eardrum when it has been perforated or punctured as the result of infection, trauma or dislodgement of a myringotomy tube (also known as a pressure equalization tube). Surgical repair of the perforation will allow the patient to recover his or her hearing and prevent repeated ear infections, particularly after swimming or shower. Traditionally, these procedures are performed using what are known as lateral and medial techniques, which require hospitalization for at least one day, and 10 to 15 days off work. Every year in Quebec, some 750 myringoplasties are performed on adult or child patients.
Details of the study
This world premiere of a new form of eardrum surgery is based on results of a four-year prospective cohort study of 208 children and adolescents, 73 of whom were treated using the new HAFGM technique. This study was published on December 16, 2011 in the scientific journal Archives of Otolaryngology – Head and Neck Surgery by Dr. Issam Saliba, otolaryngologist (ear, nose and throat or ENT specialist), surgeon and researcher at the Sainte-Justine University Hospital Centre affiliated with the Université de Montréal, where he is also professor of otology and neuro-otology. Dr. Saliba is also a surgeon and researcher at the CHUM, where he conducted a similar study, applying the same HAFGM technique to cohorts of adult patients between 2007 and 2010, with publication in the August 20, 2008 issue of the scientific journal /i>Clinical Otolaryngology and subsequently in the February 12, 2011 issue of The Laryngoscope. The University of Montreal and Sainte-Justine University Hospital Centre are known officially as Université de Montréal and Centre hospitalier universitaire Sainte-Justine, respectively.
First Pharmaceutical Cure for Tinnitus Reportedly Launched in India
Ahmedabad, India — Lincoln Pharmaceuticals announced that it has introduced the first injection pharmaceutical cure for tinnitus in India. Using the brand name Tinnex, the injection utilizes the Caroverine molecule, which was developed by Lincoln Pharma under a licensing arrangement and technical collaboration with Phafag AG, Switzerland.
According to the company, cochlear synaptic tinnitus is the most common cause of tinnitus and is due to disturbed interplay of receptors on the postsynaptic membrane between inner hair cells and dendrites. Disturbed interplay creates a state of spontaneous depolarization, causing patients to continuously hear a sound.
Tinnex is described as a glutamate antagonist with a single injection that corrects the spontaneous depolarization state. Receptors start functioning again in a normal physiological way, giving permanent cure from tinnitus to patients, the company claims. It also says that no adverse effects have been noticed during its clinical studies of the drug.
Lincoln Pharmaceuticals says it is exploring other countries to introduce Tinnex. More information is available on the company’s website.
SOURCE: News reports and Tinnex
Gene Therapy For Ears!
ScienceDaily (Dec. 19, 2011) — Normal hearing depends on the presence of healthy hair cells in the inner ear. Gene therapy has the potential to slow the loss of hair cells and promote the growth of hair cells that have already been damaged.
In gene therapy, genetic material — DNA or RNA — is transported by a carrier to cells to provide instructions for and replace damaged genes. The carrier must protect its genetic package and help it make its way through the membranes that protect cells and their surroundings. The carrier should also be able to transport the genetic material right to the cells that need help.
For the first time ever, chitosan nanoparticles have been used as a carrier for gene therapy in the ear. Chitosan is produced from shrimp shells.
“Gene therapy may someday be an alternative to using surgery to implant CI, cochlear implants, in the deaf and hard of hearing,” says Sabina Strand, at NTNU’s Department of Biotechnology.
Basic research promising
Strand studies the use of chitosan in gene therapy, and conducted this basic research, now ended, in cooperation with the Karolinska Institutet in Sweden. Here, researchers attempted to use chitosan as a carrier to deliver drugs and genes to the inner ear in guinea pigs. Chitosan was able to deliver drugs through the membrane that covers the tiny gap between the middle ear and inner ear. Chitosan was also able to deliver genes to the hair cells. Whether or not the results from guinea pigs can be transferred to human ears remains uncertain.
“However, chitosan is non-toxic and is not harmful to cells. Chitosan is therefore better than other carriers and has characteristics that mean it could potentially be used with patients,” says Strand.
Tidy packages
Chitosan is produced from powdered shrimp shells. Acid removes salts, minerals and calcium carbonate. Strong alkalis and heat remove proteins. What remains is chitosan.
Extremely small nanoparticles in the range of 50-200 nm (nanometres) are formed spontaneously when the positively charged chitosan and negatively charged genes are mixed. Chitosan does a good job packaging up DNA and RNA’s relatively large molecules.
Tailored therapy
In the body, chitosan attaches itself to molecules, cells and membranes. When the nanoparticles have passed through a membrane, chitosan packages up the gene molecules so they return to their normal size again. Chitosan also creates gaps between cells, which facilitate the absorption of medicine.
Different forms of gene therapy require nanoparticles with different properties. The properties of nanoparticles are controlled by the way in which researchers tailor the chitosan structure, its molecular size and 3D architecture. But whether or not researchers will find the perfect mix of medicines for our ears and hair cells remains to be seen — and heard.
Can hearing aids really improve my quality of life?
Yes. From the comments we receive each day, we would say that our patients are very satisfied with their hearing aids and the personalized care we provide them in managing their hearing loss. We believe that hearing aids have indeed improved their quality of life. The largest study of its kind ever conducted on hearing loss and hearing aids by the National Council on Aging found that ignoring a hearing problem can lead to depression and isolation, among other emotional problems, as compared to those who wear hearing aids. We believe hearing well does improve your quality of life. Many of our patients will attest to this!
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