# Individualized assays of supra-threshold hearing deficits

> **NIH NIH R01** · PURDUE UNIVERSITY · 2020 · $376,521

## Abstract

Abstract
Strong evidence has now emerged from animal models that noise exposure, even at levels common in
occupational and recreational settings, can cause a substantial loss of afferent synapses and nerve terminals
innervating the cochlea. Such cochlear synaptopathy does not affect hearing thresholds, and hence is
completely undetected in current standard audiological testing. Despite leaving thresholds intact, we
hypothesized that by reducing the effective number of auditory-nerve fibers, synaptopathy may degrade
suprathreshold coding of temporal information and hence explain the suprathreshold listening problems that
many listeners experience despite normal hearing thresholds (NHTs). Consistent with this, we recently
documented that among listeners with NHTs, there are large individual differences in the ability to perceive
subtle temporal features of clearly audible sounds and that these suprathreshold perceptual differences
correlate with suprathreshold coding of temporal information in the auditory brainstem. In further support of this
hypothesis, our preliminary data show that individual differences in brainstem temporal coding are already
present at the level of the auditory nerve. In the current proposal, we leverage an active hearing conservation
program led by the Purdue Audiology Clinic, and a large on-campus student marching band to directly test the
effects of occupational and recreational noise-exposure on suprathreshold hearing using parallel behavioral
and non-invasive physiological measurements. Further, to directly link the human physiological measures to
synaptopathy, we expand on an ongoing NIH project at Purdue that focuses on single-neuron and behavioral
characterizations of synaptopathic effects in an animal model (chinchilla) to include our innovative battery of
non-invasive measures. This multidisciplinary study is organized in three Specific aims: In Aim 1, we quantify
suprathreshold coding using three distinct non-invasive physiological assays that are designed to be sensitive
to synaptopathy in three separate “high-risk” human groups. In Aim 2, we quantify suprathreshold perception
using behavioral measures of temporal sensitivity and listening in noise in the same “high-risk” human groups.
In Aim 3, we will relate the same non-invasive physiological measures of coding used in humans (as in Aim 1)
to the degree of synaptopathy in the chinchilla model, as well as to objective (noise dosimetry) and
questionnaire-based estimates of noise-exposure in the human subjects. Our results will not only evaluate
clinically-viable prospective diagnostic measures of synaptopathy, but these data will advance our
understanding of the complex relationships between noise exposure, information coding by early parts of the
auditory pathway, and perceptual ability.

## Key facts

- **NIH application ID:** 9870921
- **Project number:** 5R01DC015989-04
- **Recipient organization:** PURDUE UNIVERSITY
- **Principal Investigator:** Hari Meenakshisundaram Bharadwaj
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $376,521
- **Award type:** 5
- **Project period:** 2017-03-01 → 2022-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9870921

## Citation

> US National Institutes of Health, RePORTER application 9870921, Individualized assays of supra-threshold hearing deficits (5R01DC015989-04). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9870921. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*