title: Noise-induced changes in cochlear compression in the rat as indexed by forward masking of the auditory brainstem response.
abstract: The current study was undertaken to investigate changes in forward masking patterns using on-frequency and off-frequency maskers of 7 and 10 kHz probes in the Sprague-Dawley rat. Off-frequency forward masking growth functions have been shown in humans to be non-linear, while on-frequency functions behave linearly. The non-linear nature of the off-frequency functions is attributable to active processing from the outer hair cells, and was therefore expected to be sensitive to noise-induced cochlear damage. For the study, nine Sprague-Dawley rats' auditory brainstem responses (ABRs) were recorded with and without forward maskers. Forward masker-induced changes in latency and amplitude of the initial positive peak of the rats' auditory brainstem responses were assessed with both off-frequency and on-frequency maskers. The rats were then exposed to a noise designed to induce 20-40 dB of permanent threshold shift. Twenty-one days after the noise exposure, the forward masking growth functions were measured to assess noise-induced changes in the off-frequency and on-frequency forward masking patterns. Pre-exposure results showed compressive non-linear masking effects of the off-frequency conditions on both latency and amplitude of the auditory brainstem response. The noise rendered the off-frequency forward masking patterns more linear, consistent with human behavioral findings. On- and off-frequency forward masking growth functions were calculated, and they displayed patterns consistent with human behavioral functions, both prior to noise and after the noise exposure.
authors.affiliation: Department of Speech and Hearing Science, The Ohio State University, 110 Pressey Hall, 1070 Carmack Road, Columbus, OH 43220, USA. bielefeld.6@osu.edu
authors.forename: Eric C
authors.initials: EC
authors.lastname: Bielefeld
authors.forename: Evelyn M
authors.initials: EM
authors.lastname: Hoglund
authors.forename: Lawrence L
authors.initials: LL
authors.lastname: Feth
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D001309:Auditory Threshold / Q000502:physiology; D001696:Biomechanical Phenomena; D003051:Cochlea / Q000503:physiopathology*; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology*; D006317:Hearing Loss, Noise-Induced / Q000503:physiopathology*; D006801:Humans; D008297:Male; D009622:Noise / Q000009:adverse effects; D010470:Perceptual Masking / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley