Research Roundup updates HR readers on some of the latest research and clinical findings related to hearing health care. Where appropriate, sources and original citations are provided, and readers are encouraged to refer to the primary literature for more detailed information.
Findings on How the Brain Uses Selective Hearing
Two University of California-San Francisco (UCSF) researchers have recently published a paper that reveals how humans are able to selectively hear a single speaker while tuning out other sounds in crowded or noisy environs.
To understand how selective hearing works in the brain, UCSF neurosurgeon Edward F. Chang, MD, a faculty member in the UCSF Department of Neurological Surgery and the Keck Center for Integrative Neuroscience, and UCSF postdoctoral fellow Nima Mesgarani, PhD, worked with three patients who were undergoing brain surgery for severe epilepsy.
Part of this surgery involves pinpointing the parts of the brain responsible for disabling seizures. The UCSF epilepsy team finds those locales by mapping the brain’s activity over a week, with a thin sheet of up to 256 electrodes placed under the skull on the brain’s outer surface or cortex. These electrodes record activity in the temporal lobe—home to the auditory cortex.
“The combination of high-resolution brain recordings and powerful decoding algorithms opens a window into the subjective experience of the mind that we’ve never seen before,” Chang said in the press release.
In the experiments, patients listened to two speech samples played simultaneously in which different phrases were spoken by different speakers. They were asked to identify the words they heard spoken by one of the two speakers.
The researchers then applied new decoding methods to “reconstruct” what the subjects heard from analyzing their brain activity patterns. They found that neural responses in the auditory cortex only reflected those of the targeted speaker. They found that their decoding algorithm could predict which speaker—and even what specific words—the subject was listening to based on those neural patterns. In other words, they could tell when the listener’s attention strayed to another speaker.
“The algorithm worked so well that we could predict not only the correct responses, but also even when they paid attention to the wrong word,” Chang said.
The new findings show that the representation of speech in the cortex does not only reflect the entire external acoustic environment, but instead just what we really want or need to hear. This could represent a major advance in understanding how the human brain processes language, with immediate implications for the study of impairment during aging, attention deficit disorder, autism, and language learning disorders.
Chang added that researchers could one day use this knowledge for neuroprosthetic devices for decoding the intentions and thoughts from paralyzed patients who cannot communicate.
Revealing how our brains are wired to favor some auditory cues over others may even inspire new approaches toward automating and improving how voice-activated electronic interfaces filter sounds in order to properly detect verbal commands.
The study “Selective cortical representation of attended speaker in multi-talker speech perception” by Nima Mesgarani and Edward F. Chang appears in the April 19, 2012 issue of the journal Nature.
Insomnia Worsens Tinnitus
A new report from Henry Ford Hospital shows that insomnia can have a negative effect on tinnitus, worsening the functional and emotional toll of chronic ringing, buzzing, hissing, or clicking in the head and ears. It shows a significant association between insomnia and the severity of perceived tinnitus symptoms, with patients with insomnia reporting greater emotional distress from tinnitus.
“Tinnitus involves cognitive, emotional, and psycho-physiological processes, which can result in an increase in a patient’s distress,” says study co-author Kathleen L. Yaremchuk, MD, chair of the Department of Otolaryngology-Head & Neck Surgery at Henry Ford. “Sleep complaints, including insomnia, in these patients may result in a decrease in their tolerance to tinnitus.”
The research team conducted a retrospective study of 117 patients treated between 2009 and 2011 at Henry Ford. Information was gathered from patients through telephone and written interviews using the Tinnitus Reaction Questionnaire (TRQ, which determines the emotional effects of tinnitus on a person’s lifestyle and general well-being) and the Insomnia Severity Index scales (ISI, a brief screening measure of insomnia).
Severity of TRQ was shown to be a good predictor of sleep disturbance and group association, especially the “emotional” subscore component (sensitivity 96.9% and specificity 55.3% for identifying tinnitus patients with insomnia).
The greater the insomnia disability, the more severe the patient’s complaints were regarding the tinnitus, the study finds.
“Treating patients with tinnitus is challenging,” notes Yaremchuk. “A chronic tinnitus patient presents a challenging clinical picture that may include anxiety, depression, annoyance, or self-reported emotional distress. And one of the most frequent self-reported complaints of tinnitus patients is ‘getting to sleep.'”
The study also offers further proof that evaluation and treatment of insomnia patients with tinnitus may result in a reduction in tinnitus symptom severity.
The study’s authors included Yaremchuk and George Miguel, MD, Christopher Drake, PhD, Thomas Roth, PhD, and Ed Peterson, PhD. Source: Henry Ford Hospital.
Tinnitus Patients Reportedly Benefit in Acoustic CR Neuromodulation Trial
Results of a small Phase 1 clinical trial led by Professor Peter Tass at Jülich Research Center in Germany report the use of a noninvasive technique known as Acoustic CR® Neuromodulation Reset (CR) that provided the trial’s patients with a “significant and clinically relevant decrease” in tinnitus loudness and annoyance within 12 weeks, compared to patients who received a placebo, according to the authors. CR reduces tinnitus loudness by reducing the overactivity of auditory nerve cells within the hearing portion of the brain.
The treatment involves patients wearing headphones that emit a series of tones designed to match the frequency of their individual tinnitus tones. The treatment’s emitted tones are designed to interfere and eventually disrupt the patient’s rhythmic firing patterns in the nerve cells that are believed to be causing the tinnitus.
In the prospective, randomized, single blind, placebo-controlled trial in 63 patients diagnosed with chronic tonal tinnitus and up to 50 dB hearing loss, the placebo treatment did not lead to any significant changes.
However, the effects gained by patients treated with 12 weeks of Acoustic CR persisted through a preplanned 4-week therapy pause and showed sustained long-term effects after 10 months of therapy, according to the researchers. In fact, 75% of patients had some benefit, as measured by a visual analogue scale, tinnitus questionnaire scores, and spontaneous EEG recordings.
A British Tinnitus Association spokesperson commented, “The results of this exploratory first trial are interesting and encouraging. The findings now need to be replicated by an independent research group. A randomized-controlled trial is required to assess whether this new intervention is a viable and effective treatment for tinnitus patients. We look forward to seeing the results of the planned larger scale Phase 2 Trial.”
Discovery of Hair-Cell Roots Suggests Brain Modulates Sound Sensitivity
Researchers at the University of Illinois at Chicago College of Medicine have discovered that 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.
The hair-like structures (stereocilia) are fairly rigid and are interlinked at their tops by structures called tip-links. Anna Lysakowski, professor of anatomy and cell biology at the UIC College of Medicine and principal investigator on the study, explains in the press statement that, when humans move their head, or when a sound vibration enters the 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.
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, was able to construct a composite picture of the entire top section of the hair cell.
These never-seen-before images (pictured at right) were surprising. Textbooks 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 findings were reported in the March 6, 2012 online Proceedings of the National Academy of Sciences.
Cochlear Implants for FAO Patients
Clinical researchers from University Hospitals (UH) Case Medical Center in Cleveland report that cochlear implantation provides an effective and safe way of restoring hearing in patients with far advanced otosclerosis (FAO), a hereditary condition that can lead to severe hearing loss.
“This is the first study to demonstrate that cochlear implants provide robust and long-term hearing restoration for patients with FAO,” said lead author Maroun T. Semaan, MD, an otolaryngologist with UH Case Medical Center and an assistant professor at Case Western Reserve University School of Medicine. “This is an important new treatment option for this challenging group of patients.”
FAO causes abnormal growth of bone in the middle and inner ear. This bone prevents structures within the ear from working properly, and it diminishes hearing. Hearing aids are commonly prescribed for patients with FAO. Surgery is an option with a stapedectomy, where an otologist bypasses the diseased bone with a prosthetic device that allows sound waves to be passed to the inner ear. However, in cases with advanced disease, stapedectomy surgery is not effective in restoring hearing, and the patient is essentially deaf, even with the strongest hearing aids.
The authors studied the records of 30 patients with FAO with age-matched controls who suffered from hearing loss from other causes besides FAO. They found that previous concerns about possible complications thought to potentially affect cochlear implantation in FAO patients were not seen using newer surgical techniques.
Cliff A. Megerian, MD, senior author on the study, noted, “Although a significant percentage of these patients required the additional operative step of ’round window drill out,’ this finding in no way diminished the excellent hearing outcomes enjoyed using cochlear implantation. In addition, the study showed that the presence of abnormalities on radiographic imaging did not affect hearing following implantation.”
The findings were presented at the 115th Annual Meeting of the Triological Society. Gail S. Murray, PhD, director of Audiology Services at UH Case Medical Center, was also an author on the paper.