title: Coding Deficits in Noise-Induced Hidden Hearing Loss May Stem from Incomplete Repair of Ribbon Synapses in the Cochlea.
abstract: Recent evidence has shown that noise-induced damage to the synapse between inner hair cells (IHCs) and type I afferent auditory nerve fibers (ANFs) may occur in the absence of permanent threshold shift (PTS), and that synapses connecting IHCs with low spontaneous rate (SR) ANFs are disproportionately affected. Due to the functional importance of low-SR ANF units for temporal processing and signal coding in noisy backgrounds, deficits in cochlear coding associated with noise-induced damage may result in significant difficulties with temporal processing and hearing in noise (i.e., "hidden hearing loss"). However, significant noise-induced coding deficits have not been reported at the single unit level following the loss of low-SR units. We have found evidence to suggest that some aspects of neural coding are not significantly changed with the initial loss of low-SR ANFs, and that further coding deficits arise in association with the subsequent reestablishment of the synapses. This suggests that synaptopathy in hidden hearing loss may be the result of insufficient repair of disrupted synapses, and not simply due to the loss of low-SR units. These coding deficits include decreases in driven spike rate for intensity coding as well as several aspects of temporal coding: spike latency, peak-to-sustained spike ratio and the recovery of spike rate as a function of click-interval.
authors.affiliation: Department of Physiology, Medical College of Southeast University Nanjing, China.
authors.forename: Lijuan
authors.initials: L
authors.lastname: Shi
authors.affiliation: Department of Physiology, Medical College of Southeast University Nanjing, China.
authors.forename: Yin
authors.initials: Y
authors.lastname: Chang
authors.affiliation: Department of Physiology, Medical College of Southeast University Nanjing, China.
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Li
authors.affiliation: School of Human Communication Disorders, Dalhousie University Halifax, NS, Canada.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Aiken
authors.affiliation: Department of Physiology, Medical College of Southeast University Nanjing, China.
authors.forename: Lijie
authors.initials: L
authors.lastname: Liu
authors.affiliation: Department of Physiology, Medical College of Southeast UniversityNanjing, China; School of Human Communication Disorders, Dalhousie UniversityHalifax, NS, Canada.
authors.forename: Jian
authors.initials: J
authors.lastname: Wang
keywords: auditory coding; auditory nerve fibers; hidden hearing loss; noise; ribbon synapse