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J Neurophysiol (October 8, 2003). doi:10.1152/jn.00776.2003
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Submitted on August 11, 2003
Accepted on October 3, 2003

Response growth with sound level in auditory-nerve fibers following noise-induced hearing loss

Michael G. Heinz1* and Eric D. Young1

1 Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA

* To whom correspondence should be addressed. E-mail: mgheinz{at}bme.jhu.edu.

People with sensorineural hearing loss are often constrained by a reduced acoustic dynamic range associated with loudness recruitment; however, the neural correlates of loudness and recruitment are still not well understood. The growth of auditory-nerve (AN) activity with sound level was compared in normal-hearing cats and in cats with a noise-induced hearing loss to test the hypothesis that AN-fiber rate-level functions are steeper in impaired ears. Stimuli included best-frequency and fixed-frequency tones, broadband noise, and a brief speech token. Three types of impaired responses were observed: (1) Fibers with rate-level functions that were similar across all stimuli typically had broad tuning, consistent with outer-hair-cell (OHC) damage. (2) Fibers with a wide dynamic range and shallow slope above threshold often retained sharp tuning, consistent with primarily inner-hair-cell (IHC) damage. (3) Fibers with very steep rate-level functions for all stimuli had thresholds above ~80 dB SPL and very broad tuning, consistent with severe IHC and OHC damage. Impaired rate-level slopes were on average shallower than normal for tones, and were only steeper in limited conditions. There was less variation in rate-level slopes across stimuli in impaired fibers, presumably due to the lack of suppression-induced reductions in slopes for complex stimuli relative to BF-tone slopes. Sloping saturation was observed less often in impaired fibers. These results illustrate that AN fibers do not provide a simple representation of the basilar-membrane I/O function and suggest that both OHC and IHC damage can affect AN response growth.




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E. D. Young and B. M. Calhoun
Nonlinear Modeling of Auditory-Nerve Rate Responses to Wideband Stimuli
J Neurophysiol, December 1, 2005; 94(6): 4441 - 4454.
[Abstract] [Full Text] [PDF]




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