Assessing Noise Induced Changes in Forward Masking of Wave I Latency
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Date
2012-06
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The Ohio State University
Abstract
Exposure to loud noise causes trauma to the outer hair cells (OHC), which improve hearing sensitivity and frequency discrimination. The damage done can be permanent causing a significant hearing loss. Detecting noise-induced hearing loss (NIHL) early is crucial for hearing conservation programs. The current study was undertaken as part of a larger study that looks at forward masking (FWM) of the rat auditory brainstem response (ABR). FWM causes a change in ABR response by delivering a masker sound earlier in time than the probe signal. Death of OHC creates marked changes in FWM patterns. The current study assessed FWM of the latency of wave I of an ABR wave and how it changes with NIHL due to damage to the OHC. Nine Sprague-Dawley rats were tested before and after extreme noise exposure. Probe signals at 7 kHz were used to elicit the ABR. A FWM tone was played for 40 ms followed by silence for 5 ms then a 1 ms tone burst. The Sprague-Dawley rats were then exposed to a noise band ranging from 5-10 kHz at a level of 115 dB for 90 minutes. A 21 day rest period followed to ensure permanent hearing loss. The resulting ABR waves were analyzed to calculate wave I latencies. The results demonstrated that the FWM induced a prolongation of latency in an intensity-dependent fashion. An on-frequency FWM induced linear prolongation of latency, while the off-frequency FWM required much higher levels to induce prolonged latencies. Noise exposure rendered the off-frequency masking much more linear, and similar to the on-frequency masking effects. The work suggests that latency of the ABR wave I is affected by FWM, and behaves in a manner similar to ABR amplitudes for both on- and off-frequency maskers, and before and after noise exposure.
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Keywords
Forward Masking, Outer Hair Cells, Auditory Brainstem Response, Noise-Induced Hearing Loss