Effects of periodic rest on physiological measures of auditory sensitivity following exposure to noise.
Sinex-DG; Clark-WW; Bohne-BA
J Acoust Soc Am 1987 Oct; 82(4):1265-1273
The effect of intermittent noise on auditory sensitivity was studied in chinchillas. Chinchillas surgically implanted with microphones and microelectrodes were exposed to an octave band of noise centered at 0.5 kilohertz (kHz) with a sound pressure level of 95 decibels (dB) and presented intermittently at the rate of 15 minutes per hour for 4 or 40 days. Whole nerve action potentials (APs) and single auditory nerve fiber thresholds in response to click and tone stimuli were measured at the end of the exposure periods. The animals were then killed, and their cochleas were removed and examined for histopathological changes. AP thresholds were elevated by approximately 40dB for noise frequencies of 0.5 to 8kHz by day 4. By day 40 these shifts had decreased to 10 to 25dB. Tuning curves on single fiber response (plots of threshold versus frequency) determined on day 4 were abnormal. By day 40 the low frequency curves appeared to be more nearly normal. In some exposed animals characteristic frequency gaps were seen in the lowest unit thresholds. Patterns of cochlear hair cell loss were similar on days 4 and 40. Moderate loss of outer hair cells occurred in the upper turns of the cochlea, although very little loss of inner hair cells was seen. The extent of outer hair cell loss was not correlated with the magnitude of the AP shift or the frequency range in which the shift occurred. The authors conclude that the initial threshold shifts and partial recovery of sensitivity that occur after exposure originate in the cochlea. The reason for the observed recovery is not known.
NIOSH-Publication; NIOSH-Grant; Inner-ear; Anatomy; Histopathology; Noise-exposure; Sensory-thresholds; In-vivo-studies; Laboratory-animals; Electrophysiology; Noise-induced-hearing-loss
Research Central Inst for the Deaf 818 South Euclid St Louis, MO 63110
Journal of the Acoustical Society of America
Central Institute for the Deaf, Saint Louis, Missouri