Speaker
Description
Cochlear synaptopathy is a common pathology involving damage to and loss of auditory-nerve synapses with inner hair cells. Cochlear synaptopathy is undetectable with the clinical audiogram and widely thought to cause hearing-in-noise problems known as hidden hearing loss. Animal models are advantageous for studying links between cochlear synaptopathy and hidden hearing loss because synaptic injury can be induced and readily quantified. We induced excitotoxic cochlear synaptopathy in budgerigars, a parakeet, using intracochlear kainic-acid infusions. Budgerigars were selected based on extensive prior research showing human-like perception of complex sounds. Effects of synaptopathy on auditory perception and neural processing were evaluated with operant-conditioning behavioral experiments and single-unit auditory-nerve recordings, respectively. Many aspects of auditory perception were normal following kainic-acid infusions including the audiogram, temporal integration, and sensitivity to differences in envelope statistics. Behavioral impairment was observed for detection of tone pips at the onset of a simultaneous noise burst. The result suggests selective impairment of acoustic onset-cue perception. Single-unit auditory-nerve recordings showed that perceptual changes were associated with increased spontaneous activity and onset excitability of surviving fibers. Increased excitability of auditory-nerve responses following synaptic injury may contribute to impaired onset-cue perception with cochlear synaptopathy.