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Cochlear neuropathy and the coding of supra-threshold sound.
Hari M Bharadwaj1, Sarah Verhulst2, Luke Shaheen3
1Center for Computational Neuroscience and Neural Technology, Boston University Boston, MA, USA ; Department of Biomedical Engineering, Boston University Boston, MA, USA.
Frontiers in Systems Neuroscience
|March 7, 2014
Summary
Many people with normal hearing struggle with sound perception and speech understanding due to impaired supra-threshold encoding. Cochlear neuropathy may cause these deficits, impacting auditory nerve fibers and leading to difficulties even with normal hearing thresholds.
Area of Science:
- Auditory Neuroscience
- Neuroscience
- Speech Perception
Background:
- Many individuals with clinically normal hearing thresholds report difficulties in everyday listening and speech-in-noise comprehension.
- Sub-threshold auditory processing, particularly the temporal precision of sound encoding in the early auditory pathway, is implicated in these listening challenges.
- Auditory subcortical steady-state responses (SSSRs) and behavioral measures in humans and animals suggest impaired temporal coding can occur despite normal audiograms.
Purpose of the Study:
- To explore the hypothesis that cochlear neuropathy, a condition affecting auditory nerve fibers (ANFs), contributes to deficits in supra-threshold sound encoding.
- To investigate the link between ANF loss, reduced encoding precision, and behavioral/electrophysiological manifestations in individuals with normal hearing thresholds (NHTs).
- To propose objective measures for detecting supra-threshold coding deficits associated with neuropathy and discuss clinical implications.
Main Methods:
- Analysis of auditory subcortical steady-state responses (SSSRs) in humans and animal models.
- Behavioral testing in humans with NHTs, focusing on tasks requiring detailed spectro-temporal analysis (e.g., frequency modulation discrimination).
- Review of animal studies examining the effects of noise exposure and aging on ANF populations and audiograms.
Main Results:
- Impaired temporal coding precision in the early auditory pathway can exist even with normal hearing thresholds.
- Noise exposure and aging can lead to significant ANF loss without altering audiometric thresholds.
- Individual differences in supra-threshold processing in humans correlate with subcortical temporal coding precision.
Conclusions:
- Cochlear neuropathy is a potential cause of reduced supra-threshold sound encoding precision, manifesting in both behavioral difficulties and altered SSSRs.
- Noise-induced neuropathy may selectively affect specific types of ANFs (higher-threshold, lower-spontaneous-rate).
- Developing objective measures for supra-threshold coding deficits is crucial for understanding and potentially treating listening difficulties associated with neuropathy.
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