cochlear nerve damage

Developing Better Tests for Discovering “Hidden” Hearing Loss

By Hari Bharadwaj, Ph.D., with Inyong Choi, Ph.D.

Conventionally, hearing loss is thought to be a consequence of damage to delicate sensory hair cells in the inner ear (cochlea). However, over the past decade animal studies have shown that nerve endings in the cochlea are considerably more vulnerable to damage than the sensory hair cells, and that such nerve damage is likely to happen before conventionally recognized forms of hearing loss occur.

Emerging Research Grants (ERG) recipients Bharadwaj and Choi, and colleagues, systematically investigated the many sources of variability that obscure cochlear nerve damage (“synaptopathy”) to provide recommendations for how best to measure such nerve damage.

Emerging Research Grants (ERG) recipients Bharadwaj and Choi, and colleagues, systematically investigated the many sources of variability that obscure cochlear nerve damage (“synaptopathy”) to provide recommendations for how best to measure such nerve damage.

Unfortunately, damage to cochlear nerve endings cannot be detected by current clinical hearing tests. Yet, this “hidden” damage can hypothetically still affect hearing in everyday noisy environments such as crowded restaurants and busy streets. Therefore, it is important to develop tests to detect such damage in humans, and there is considerable interest among hearing scientists toward this enterprise.

In our paper published in Neuroscience on March 8, 2019, we considered noninvasive tests that can potentially reveal such nerve damage and systematically investigated other extraneous sources of variability that might reduce the sensitivity and specificity of these tests. This helped us come up with recommendations for how we can best apply these tests. Funding from Hearing Health Foundation’s Emerging Research Grants contributed to experiments that helped understand and articulate the role of two key variables: how variations in the anatomy of individuals (e.g., brain shape and size) affected our noninvasive tests; and how certain cognitive factors like attention may affect hearing independently of how well the inner ear is capturing the information in sounds.

Armed with the knowledge about these variables and other factors described in the paper, we anticipate that hearing scientists will be able to design more powerful experiments to understand the effects of damage to cochlear nerve endings, and build more powerful tests to detect such damage in the clinic. This work is crucial in enabling clinical translation of the basic science that has been uncovered over the past decade.

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A 2015 Emerging Research Grants (ERG) scientist, Hari Bharadwaj, Ph.D., is an assistant professor at Purdue University in Indiana with a joint appointment in speech, language, and hearing sciences, and biomedical engineering. Inyong Choi, Ph.D., is an assistant professor in the department of communication sciences and disorders at the University of Iowa. Choi’s 2017 ERG grant was generously funded by the General Grand Chapter Royal Arch Masons International.

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