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Discharge patterns in the cochlear nucleus of the chinchilla following noise induced asymptotic threshold shift.

Salvi-RJ; Hamernik-RP; Henderson-D
Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, R01-OH-00364, 1981 Jan; :1-31
A NIOSH sponsored study was conducted to determine the discharge patterns in the cochlear nucleus of the chinchilla following noise induced asymptotic threshold shift. Chinchillas were exposed to 86dB SPL octave band of noise centered at 4kHz for 3.5 to 5 days. Three of the animals were trained in behavioral audiometry (shock avoidance at the sound of a series of tones) and were used to measure the time course and magnitude of the noise induced hearing deficit; the remaining eight animals were used for neural and histological studies. Behavioral tests indicated that the hearing deficit induced by noise exposure was between 4 and 16kHz, and threshold shift was between 40 and 74dB SPL, depending on the frequency and time after recovery. Measurements from cochlear single neurons revealed abnormalities in the responses of neurons with characteristic frequencies above 2kHz. Units above 2kHz had elevated frequencies (50 to 90dB SPL) and broad tuning curves due to a greater loss of sensitivity near characteristic frequencies than at low frequencies. Units above 2Khz also displayed low spontaneous activity rates. Cochleagrams obtained 12 hr postexposure revealed discrete hair cell lesions in the basal third of the cochlea; the locations of the lesions correlated with the frequencies of maximum loss of hearing. Behavioral thresholds and thresholds of characteristic frequencies of the most sensitive units were within 10 to 15dB of each other. Results are taken to indicate that intense sound reduces the sensitivity, frequency selectivity and spontaneous activity of units in the cochlear nucleus.
NIOSH-Grant; Noise-levels; Physiology; Sensory-perceptual-processes; Hearing-disorders; Hearing-tests; Hearing-loss
Otolaryngology Upstate Medical Center Departm 750 E Adams Street Syracuse, N Y 13210
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National Institute for Occupational Safety and Health
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Upstate Medical Center, Syracuse, New York
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division