Hearing loss and cochlear pathology in monkeys after noise exposure

Old World monkeys were exposed to octaveband noise from 0.5 to 8 kHz at 120 dB SPL, 8 hours daily for 20 days. Restricted permanent threshold shifts and localized loss of outer hair cells were produced, which were reasonably well correlated with the exposure frequencies. There was also a loss of both inner and outer hair cells at the extreme basal end of Corti's organ, regardless of the exposure frequency. Implications for human inner ear pathology are discussed.