Location Discovered of Genes That May Be Responsible for Age-Related High Frequency Hearing Loss

A study published in the April 27 open access journal BMC Genetics reports the finding of the genetic loci (the position of genes on the chromosome) that specifically pertain to age-related high frequency hearing loss.

Presbycusis is the loss of hearing for high-pitched sounds that gradually occurs in most individuals as they grow older. Although many genetic loci have been linked to hearing deficits in humans, many loci that contribute to tonotopy, or the organization of the auditory system that permits detection and discrimination of sounds of different frequency, remain undiscovered.

A group from the National Institute on Deafness and Other Communication Disorders at the National Institutes of Health (NIH) used genome-wide linkage analysis in NIH Swiss mice to successfully identify two quantitative trait loci that affect hearing at high frequencies—Hfhl1 and Hfhl3. Specifically, the effect of the locus Hfhl1 is thought to be confined to hearing frequencies from 25 to 44 kHz of the tonotopic map, while Hfhl3 is restricted to the 35 to 44 kHz region.

Lead author James M. Keller commented in the press release, “Our results support the hypothesis that frequency-specific hearing loss results from variation in gene activity along the cochlear partition and suggest a strategy for creating a map of genes that influence differences in hearing sensitivity and/or vulnerability in restricted portions of the cochlea.”

Keller cautioned, however, that the high-frequency hearing loss loci, Hfhl1 and Hfhl3, explain only a portion of the variation in high-frequency hearing loss observed in these mice. “Other loci, and cross talk between genes at different loci, probably account for much of the remainder,” says Keller. “In fact, we detected a number of additional loci that could account for some of the residual variation. Additional genotyping and analysis could greatly increase our understanding of the genetic architecture of the HFHL phenotype.” The study can be accessed at: tinyurl.com/8982hdt

Circuitry
Support for Theory that Blindness May Rapidly Enhance Other Senses

New findings from a Canadian research team investigating the link between blindness and enhanced hearing suggest that not only is there a real connection between vision and other senses, but the connection is important to better understanding the underlying mechanisms that can quickly trigger sensory changes.

The research may demystify the true potential of human adaptation and, ultimately, help develop innovative and effective methods for rehabilitation following sensory loss or injury.

François Champoux, director of the University of Montreal’s Laboratory of Auditory Neuroscience Research, presented his team’s findings at the Acoustics 2012 meeting in Hong Kong.

Studies have shown, in terms of hearing, that blind people are better at localizing sound. One study even suggested that blindness might improve the ability to differentiate between sound frequencies. “The supposed enhanced tactile abilities have been studied at a greater degree and can be seen as early as days or even minutes following blindness,” says Champoux. “This rapid change in auditory ability hasn’t yet been clearly demonstrated.”

Two big questions about blindness and enhanced abilities remain unanswered: Can blindness improve more complex auditory abilities and, if so, can these changes be triggered after only a few minutes of visual deprivation, similar to those seen with tactile abilities?

“When we speak or play a musical instrument, the sounds have specific harmonic relations. In other words, if we play a certain note on a piano, that note has many related ‘layers.’ However, we don’t hear all of these layers because our brain simply associates them all together and we only hear the lowest one,” Champoux explains.

It is through this complex computation, based on specific components of the sound, that the brain can interpret and distinguish auditory signals coming from different people or instruments. The ability to identify harmonicity (the harmonic relation between sounds) is one of the most powerful factors involved in interpreting our auditory surroundings.

“Harmonicity can easily be evaluated using a simple task in which similar harmonic layers are set up and one of them is gradually modified until the individual notices two layers instead of one,” says Champoux. “In our study, healthy individuals completed such a task while blindfolded. This task was administered twice, separated by a 90-minute interval during which the participants conversed with the experimenter in a quiet room. Half of the participants kept the blindfold on during the interval period, depriving them of all visual input, while the other half removed their blindfolds.”

They found no significant differences between the two groups in their ability to differentiate harmonicity prior to visual deprivation. However, the results of the testing session following visual deprivation revealed that visually deprived individuals performed significantly better than the group that took their blindfolds off.

“Regardless of the neural basis for such an enhancement, our results suggest that the potential for change in auditory perception is much greater than previously assumed,” Champoux notes.

Cone Beam CT Better for Visualizing Some Causes of Hearing Loss at Half the Radiation Dose

Cone beam CT has been shown to be superior to multidetector CT for detecting superior semicircular canal dehiscence or the so-called third window (a small hole in the bony wall of the inner ear bone that can cause dizziness and hearing loss), a new study shows. In addition, the technology uses half the radiation dose.

The study, conducted in Bruges, Belgium, included 21 patients who had both a cone beam CT and a multidetector CT examination of their right and left temporal bones, said David Volders, MD, one of the authors of the study.

Two radiologists reviewed the images from both exams and scored them based on image quality and the presence of pathology. The study found that cone beam CT “corrected a false positive diagnosis for superior semicircular canal dehiscence in 11 out of 16 cases which were positive on multidetector CT (68.8%),” said Volders. Multidetector CT had indicated there was a dehiscence of the superior semicircular canal, when there wasn’t, he added. Cone beam CT also scored significantly better than multidetector CT in visualizing normal temporal bone anatomy.

“In our facility, all patients who undergo temporal bone imaging to diagnose fractures, congenital middle ear deformities, chronic ear infections, and conductive hearing loss are now scanned with cone beam CT,” said Volders in the press release. “The significantly better image quality and the very low radiation dose have made cone beam CT our main choice for temporal bone imaging.”

While apparently more effective, cone beam CTs are uncommon in radiology centers, and Volders urged colleagues to monitor their development as they improve and can be utilized for more uses.

The study was presented May 2, 2012 at the American Roentgen Ray Society Annual Meeting in Vancouver, Canada.

Researchers Developing Middle-Ear Microphone for Cochlear Implants

Currently, surgically implanted cochlear implant microphones and related electronics must be worn outside the head, raising reliability issues—as well as social and cosmetic considerations—and preventing patients from swimming. Now, a University of Utah engineer and colleagues in Ohio have developed a tiny prototype microphone that can be implanted in the middle ear.

The proof-of-concept device (pictured) has been successfully tested in the ear canals of four cadavers, the researchers report in a study published online in the Institute of Electrical and Electronics Engineers (IEEE) journal Transactions on Biomedical Engineering accessed at: http://tinyurl.com/76v9rsa.

While the prototype is about the size of an eraser on a pencil, the device isn’t ready for human tests yet. The developers still want to reduce the size and improve its ability to detect quieter, low-pitched sounds, so human trials are about 3 years away, says the study’s senior author, Darrin J. Young, associate professor of electrical and computer engineering at the University of Utah and USTAR, the Utah Science Technology and Research initiative.

The study showed incoming sound is transmitted most efficiently to the microphone if surgeons first remove the incus or anvil. Of course, US Food and Drug Administration approval would be needed for an implant requiring such surgery.

The current prototype of the packaged, middle-ear microphone measures 2.5-by-6.2 mm (roughly one-tenth by one-quarter inch) and weighs 25 mg, or less than a thousandth of an ounce. Young wants to reduce the package to 2-by-2 mm.

In traditional cochlear implants, the microphone, signal processor and transmitter coil are worn outside the head and send signals to the internal receiver-stimulator, which is implanted in bone under the skin and sends the signals to the electrodes implanted in the cochlea to stimulate auditory nerves. The ear canal, eardrum, and hearing bones are bypassed.

The system developed by Young implants all the external components. Sound moves through the ear canal to the eardrum, which vibrates as it does normally. But at the umbo, a sensor known as an accelerometer is attached to detect the vibration. The sensor also is attached to a chip, and together they serve as a microphone that picks up the sound vibrations and converts them into electrical signals sent to the electrodes in the cochlea.

The device still would require patients to wear a charger behind the ear while sleeping at night to recharge an implanted battery. Young says he expects the battery would last one to several days between charging.

Young says the microphone also might be part of an implanted hearing aid that could replace conventional hearing aids for a certain class of patients who have degraded hearing bones unable to adequately convey sounds from conventional hearing aids.

Young conducted the study with Mark Zurcher and Wen Ko, and with ENT physicians Maroun Semaan and Cliff Megerian of University Hospitals Case Medical Center.

To hear a recording of the start of Beethoven’s Ninth Symphony through the new microphone implanted in a cadaver’s middle ear, go to http://ow.ly/aOoMp.