The proposed experiments aim to determine how the consequences of asymmetric hearing loss (AHL) in auditory cortex affect the neural processes that allow listeners to parse and decode foreground sounds in background noise. AHL is one of the most common forms of hearing impairment, and it profoundly disrupts spatial hearing and the ability to process signals in noise (SIN). Disabilities across hearing domains are generally more severe in AHL patients than in equivalent cases of symmetric sensorineural hearing loss (SNHL). Thus, AHL has broad implications for health, including tinnitus, cognitive impairment, and reduced quality of life. We recently discovered that the cortical hemispheres ipsilateral and contralateral to the hearing loss recover differently after asymmetric acoustic trauma. Specifically, spectral preferences for sounds emanating from the two ears realign in the contralateral hemisphere within ~6 months after AHL but remain misaligned in the ipsilateral hemisphere. Neither the dynamics nor the functional consequences of these hemispheric differences on SIN processing or crucial auditory functions such as central gain adaptation are known. Furthermore, we recently discovered that neurons in normal auditory cortex are considerably diverse in how well they tolerate background noise. Some neurons actually improving their processing in the presence of noise. This diversity creates an opportunity to identify the factors that determine the noise tolerance of cortical neurons and the consequences of AHL. We propose to conduct a multifaceted, longitudinal analysis of bilateral cortical reorganization following AHL. The role of inhibitory interneurons is of special interest because inhibitory dysregulation has been implicated as both a cause and consequence of hearing loss.
Our Aims will determine (1) how AHL affects the sensitivity to background sounds in the cortical circuits, (2) how AHL affects the ability of cortical neurons to adapt to changes in stimulus level and contrast, and (3) how functional changes in AHL relate to the structural and functional expression of inhibition in cortical networks. We will estimate spectral and temporal tuning properties, excitatory-inhibitory balance, and temporal context capabilities, which are all critical for optimal speech perception. We will provide the first examination of disrupted cortical SIN processing in AHL by studying monaural and binaural signal decoding abilities over a range of competing background noise levels. We will relate the degree and time course of AHL-induced functional processing changes to neuroanatomically determined alterations in the interneuron density across core cortical fields in the two hemispheres. The wealth of new insights generated by this approach will resolve numerous outstanding questions regarding central reorganization in AHL and its dynamic time course, equip clinical researchers with new and better-defined central biomarkers of AHL, facilitate the development of improved rehabilitation strategies, and provide a new way to understand how the brain extracts signals from noise in normal and impaired hearing.

Public Health Relevance

The principal difficulty faced by people with asymmetric peripheral hearing loss is a reduction in speech comprehension due to the competing background noise present in typical listening environments. This project explores the consequences of asymmetric hearing loss on hemisphere-specific cortical stimulus coding principles that enable robust signal-in-noise processing. Knowledge of these principles will guide the development of novel therapeutic approaches to communicative disorders, such as possibilities of behavioral training, algorithms for noise reduction in hearing aids, and stimulation protocols for neural prosthetic devices for hearing.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
1R01DC017396-01
Application #
9615738
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Poremba, Amy
Project Start
2018-07-10
Project End
2023-06-30
Budget Start
2018-07-10
Budget End
2019-06-30
Support Year
1
Fiscal Year
2018
Total Cost
Indirect Cost
Name
University of California San Francisco
Department
Otolaryngology
Type
Schools of Medicine
DUNS #
094878337
City
San Francisco
State
CA
Country
United States
Zip Code
94118