2016

Julia Campbell, Ph.D., Au.D.

Julia Campbell, Ph.D., Au.D.

University of Texas at Austin
Auditory gating in tinnitus

Tinnitus is the perception of sound, such as ringing or buzzing, without an external source. Though tinnitus likely arises, in part, from hearing loss in the inner ear, research has determined that the ongoing perception of tinnitus occurs in the brain. It has been suggested that auditory gating, a function carried out by the brain in filtering out unimportant auditory information, may be abnormal in individuals with tinnitus and contribute to the conscious perception of the phantom sound.

Auditory gating can be measured noninvasively through the brain’s cortical response to sound during recording of brainwave activity, known as EEG (electroencephalography). In typical auditory gating function, cortical auditory evoked potentials (CAEPs) recorded during EEG show a decrease in amplitude when sounds (e.g., tone pairs) are presented close together in time. This decrease in amplitude reflects the brain’s ability to filter out repetitive auditory input. In atypical gating function, CAEP amplitude remains the same across sound presentation or shows little change, again suggestive of the brain’s inability to filter out irrelevant input.

This study aims to evaluate auditory gating processes in tinnitus, including cortical sources of active gating networks as observed through source localization analyses. These results will be correlated with subject reports of tinnitus severity.

Richard A. Felix II, Ph.D.

Richard A. Felix II, Ph.D.

Washington State University Vancouver
Neural mechanisms underlying deficits encoding temporal sound features associated with central auditory processing disorder

A critical function of the auditory system is to extract meaning from complex sounds. When this basic function is impaired, quality of life can be greatly affected. This is particularly true for speech processing, where degrading temporal information significantly alters the ability to listen. Difficulty encoding temporal cues is a hallmark central auditory processing disorder (CAPD), which is also marked by problems understanding complex sounds despite normal function of the peripheral auditory system. The origin of deficits associated with CAPD has been localized to the brain, but the neural mechanisms underlying the encoding of temporal sound cues remain poorly understood.

The goal of this research is to examine the contributions of inhibitory connections to the midbrain, the first known site in the auditory pathway that exhibits abnormal function in those with CAPD. These midbrain inputs signal temporal sound features important in the emergence of CAP and might therefore play an important role in the generation of listening problems. The results of this project will be a key step in advancing our understanding of how the processing of temporal information at the level of brain circuits relate to deficits associated with CAPD.

Xiying Guan, Ph.D.

Xiying Guan, Ph.D.

Mass Eye and Ear, Harvard Medical School
Hyperacusis caused by abnormalities in auditory mechanics

Many hyperacusis patients have what is called “conductive hyperacusis,” due to mechanical abnormalities of the ear that result in a hypersensitivity to sounds/vibrations transmitted through their bodies. These include the sensation of one’s own voice (autophony), pulse, and body movements such as eye motion and footsteps, as well as sensing the vibrations of items such as vehicles. These symptoms are common among patients who have an opening in the bone encapsulating the inner ear (termed a superior canal dehiscence, a type of pathological third-window lesion).

Compared with hyperacusis stemming from neurosensory issues, conductive hyperacusis has the potential for treatment. Recently, surgical treatment for hyperacusis by changing the mechanics of surrounding structures of the inner ear show mixed results, with some patients experiencing worse symptoms after surgery.

Although these “experimental” surgical treatments in patients are increasing, the mechanisms of conductive hyperacusis are not well understood, and scientific research targeting this problem is lacking. This study aims to understand how mechanical changes in fresh cadaveric specimens with similar gross mechanics as the living can influence the cochlear input drive (an estimate of hearing), resulting in hyperacusis. Our novel intracochlear pressure measurement technique will allow the monitoring of the cochlear input drive as we manipulate the mechanics surrounding the inner ear.

Nathan Higgins, Ph.D.

Nathan Higgins, Ph.D.

Vanderbilt University
Biomarkers of spatial processing in auditory cortex measured with functional near-infrared spectroscopy

Central auditory processing disorders (CAPD) comprise a number of functional deficits, such as impairments in the ability to process complex information used for localizing, fusing, and discriminating acoustic objects or streams. Binaural hearing (integrating information from the two ears) represents a fundamental aspect of central auditory processing and can be objectively measured in the brain using biomarkers such as the blood oxygenation level-dependent (BOLD) signal in the auditory cortex.

Functional near-infrared spectroscopy (fNIRS) is an emerging technique for measuring the BOLD signal, and is well suited for study of CAPD clinically due to its low noise, portability, and cost effectiveness. As a clinical tool for objective measures of central auditory processing, fNIRS has a bright future. This project will measure fNIRS sensitivity to binaural tuning of BOLD responses, testing the hypothesis of broad contralateral tuning as seen with fMRI. Attention will be manipulated by tasks requiring feature detection in different modalities (location, pitch, visual). Also to be measured is the effect of task engagement on the BOLD signal, compared with passive listening, in order to yield an objective biomarker of cortical processing for task-related attention. This is an important tool when examining clinical populations (e.g. young children) who are unable to provide reliable feedback.

Gail Ishiyama, M.D.

Gail Ishiyama, M.D.

UCLA David Geffen School of Medicine
Cellular and molecular biology of the microvasculature in the macula utricle of patients diagnosed with Ménière’s disease

To investigate the microscopic structure of the vasculature (blood vessel system) of balance organs from patients with intractable Ménière’s disease. Ishiyama’s hypothesis is that altered biochemical pathways affecting the vasculature of the blood labyrinthine barrier—which protects the inner ear from toxins and infections—may cause a dysfunction of the inner ear, leading to hearing loss and vertigo.

Ishiyama’s recent research revealed structural cellular changes in the blood labyrinthine barrier of the utricle, a balance organ, in Ménière’s patients. This project continues the work by detailing the cells and biochemical pathways that are altered in Ménière’s disease. This will provide greater information on the blood labyrinthine barrier and allow for the development of interventions that prevent the progression of hearing loss and stop the disabling vertigo in Ménière’s disease patients.

Harrison W. Lin, M.D.

Harrison W. Lin, M.D.

University of California, Irvine
Objective and subjective suprathreshold measures of auditory neurodegeneration

Recent research on animals convincingly demonstrates that degeneration of the auditory nerve, called auditory neurodegeneration, will result from a brief, moderate noise exposure. These animals suffered from severe, permanent deterioration of the function and microscopic appearance of the auditory nerve from a seemingly short, innocuous noise exposure. Interestingly, the animal’s ability to recognize the presence of sound fully recovered to normal threshold levels following the trauma.

However, when presented with sound levels above their ability to hear (“suprathreshold” levels), the strength of the electric signals from the auditory nerve was reduced by as much as 50 percent in some frequencies. Because standard hearing tests (audiograms) of these noise-exposed animals were indistinguishable from unexposed animals, the phenomenon of auditory neurodegeneration may result in a “hidden hearing loss,” and moreover, play a key role in the development of tinnitus, hyperacusis, and other auditory processing abnormalities.

Many military personnel who are subject to severe noise trauma and blast injuries subsequently develop chronic, oftentimes debilitating, tinnitus, and it is thought that this auditory neurodegeneration phenomenon is at least partially responsible for these symptoms. But auditory neurodegeneration in humans has not been established, and its perceptual consequences, including tinnitus, remain unknown. This project aims to establish the missing link between animal and human studies on auditory neurodegeneration and to provide quantitative and qualitative assessment of perceptual consequences of neurodegeneration.

Elizabeth McCullagh, Ph.D.

Elizabeth McCullagh, Ph.D.

University of Colorado
The role of the MNTB in sound localization impairments in autism spectrum disorder

The processing of sound location and the establishment of spatial channels to separate several simultaneous sounds is critical for social interaction, such as carrying on a conversation in a noisy room or focusing on a person speaking. Impairments in sound localization can often result in central auditory processing disorders (CAPD). A form of CAPD is also observed clinically in all autism spectrum disorders, and is a significant to quality-of-life issues in autistic patients.

The circuit in charge of initially localizing sound sources and establishing spatial channels is located in the auditory brain stem and functions with precisely integrated neural excitation and inhibition. A recent theory posits that autism may be caused by an imbalance of excitatory and inhibitory synapses, particularly in sensory systems. An imbalance of excitation and inhibition would lead to a decreased ability to separate competing sound sources. While the current excitation to inhibition model of autism assumes that most inhibition in the brain is GABAergic, the sound localization pathway in the brainstem functions primarily with temporally faster and more precise glycinergic inhibition.

The role of glycinergic inhibition has never been studied in autism disorders, and could be a crucial component of altered synaptic processing in autism. The brainstem is a good model to address this question since the primary form of inhibition is through glycine, and the ratio of excitation to inhibition is crucial for normal processing.

Rahul Mittal, Ph.D.

Rahul Mittal, Ph.D.

University of Miami Miller School of Medicine
Deciphering the role of Slc22a4 in the development of stria vascularis, and to determine the effect of supplementation of its antioxidant substrate ergothioneine, on age-related hearing loss

Since mutations in the SLC22 gene family have been implicated in various pathological conditions, there has been a renewed interest in understanding their role in the maintenance of normal physiological functions of cells. SLC22A4 is ubiquitously expressed in the body and transports across the cellular plasma membrane various compounds, including acetylcholine and carnitine as well as the naturally occurring antioxidant ergothioneine (ERGO). In addition, SLC22A4 is abundantly expressed in the stria vascularis (SV), but its role in SV biology is not known.

This project will help in understanding how SLC22A4 contributes to SV development, atrophy, and dysfunction of the cochlea, leading to hearing loss. The project also aims to determine whether ERGO supplementation can prevent SV atrophy and ameliorate age-related hearing loss (presbycusis) in a mouse model.

Nirmal Kumar Srinivasan, Ph.D.

Nirmal Kumar Srinivasan, Ph.D.

Towson University
Understanding and decoding CAPD in adults

Understanding speech in complex listening environments involves both on top-down and bottom-up processes. Central auditory processing disorder (CAPD) refers to a reduction in the efficiency and effectiveness of how the central nervous system utilizes the presented auditory information. It is characterized by a diminished perception of speech and non-speech sounds that is not attributable to peripheral hearing loss or intellectual impairment. Hearing loss and CAPD can adversely affect everyday communication, learning, and physical well-being.

A substantial number of adults evaluated for CAPD complain about difficulties in resolving auditory events that are similar to that of individuals with hearing impairment. These individuals have audiograms that are similar to those of age-matched individuals. Since the audiogram is the primary tool used in the clinic to distinguish people with hearing loss, it is imperative to understand the fundamental differences observed in behavioral experiments for individuals with CAPD and individuals with hearing loss.

Sign up to receive groundbreaking hearing and balance research updates.