Effects of cochlear-synaptopathy inducing moderate noise exposure on auditory-nerve-fiber responses in chinchillas

It has been hypothesized that selective loss of low-spontaneous-rate (low-SR) auditory-nerve (AN) fibers following moderate noise exposure may underlie perceptual difficulties some people experience in noisy situations, despite normal audiograms. However, the finding of selective low-SR-fiber loss has not been replicated in an animal model with behavioral thresholds similar to humans. We recently established a behavioral chinchilla model for which neural and behavioral AM-detection thresholds are in line with each other and similar to humans. Here, we report physiological AN-fiber response properties from anesthetized chinchillas exposed to noise that produced cochlear synaptopathy, as confirmed by immunofluorescence histology. Auditory-brainstem responses, distortion-product otoacoustic emissions, and compound action potentials confirmed no significant permanent threshold shift. Stimuli included both simple (pure tones, as studied previously) and complex (broadband noise) sounds. Low-SR fibers were reduc...