Affiliation:
1. Kresge Hearing Research Institute, Department of Otolaryngology University of Michigan Ann Arbor MI USA
2. Instituto de Neurociencias de Castilla y León Universidad de Salamanca Salamanca Spain
3. Department of Molecular and Integrative Physiology University of Michigan Ann Arbor MI USA
4. Department of Biomedical Engineering University of Michigan Ann Arbor MI USA
Abstract
AbstractHearing impairment without threshold elevations can occur when there is damage to high‐threshold auditory nerve fibre synapses with cochlear inner hair cells. Instead, cochlear synaptopathy produces suprathreshold deficits, especially in older patients, which affect conversational speech. Given that listening in noise at suprathreshold levels presents significant challenges to the ageing population, we examined the effects of synaptopathy on tone‐in‐noise coding on the central recipients of auditory nerve fibres, i.e. the cochlear nucleus neurons. To induce synaptopathy, guinea pigs received a unilateral sound overexposure to the left ears. A separate group received sham exposures. At 4 weeks post‐exposure, thresholds had recovered but reduced auditory brainstem response wave 1 amplitudes and auditory nerve synapse loss remained on the left side. Single‐unit responses were recorded from several cell types in the ventral cochlear nucleus to pure‐tone and noise stimuli. Receptive fields and rate–level functions in the presence of continuous broadband noise were examined. The synaptopathy‐inducing noise exposure did not affect mean unit tone‐in‐noise thresholds, nor the tone‐in‐noise thresholds in each animal, demonstrating equivalent tone‐in‐noise detection thresholds to sham animals. However, synaptopathy reduced single‐unit responses to suprathreshold tones in the presence of background noise, particularly in the cochlear nucleus small cells. These data demonstrate that suprathreshold tone‐in‐noise deficits following cochlear synaptopathy are evident in the first neural station of the auditory brain, the cochlear nucleus neurons, and provide a potential target for assessment and treatment of listening‐in‐noise deficits in humans.
imageKey points
Recording from multiple central auditory neurons can determine tone‐in‐noise deficits in animals with quantified cochlear synapse damage.
Using this technique, we found that tone‐in‐noise thresholds are not altered by cochlear synaptopathy, whereas coding of suprathreshold tones‐in‐noise is disrupted.
Suprathreshold deficits occur in small cells and primary‐like neurons of the cochlear nucleus.
These data provide important insights into the mechanisms underlying difficulties associated with hearing in noisy environments.
Funder
National Institute on Deafness and Other Communication Disorders
Royal National Institute for Deaf People
Cited by
1 articles.
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