Relationship between the auditory brainstem response and auditory nerve thresholds in cats with hearing loss

This study explored the relationship between the auditory brainstem respons e (ABR) and auditory serve sensitivity in cats with normal hearing and with noise-induced permanent threshold shifts. A statistically significant line ar correlation was found between each cat's ABR thresholds and the most sen sitive single neuron thresholds at the same frequency. ABR thresholds were approximately 25 dB higher than the thresholds of the most sensitive neural responses in cats with normal hearing. The two measures produced equivalen t thresholds at impaired frequencies in subjects with sensorineural hearing loss. Two factors may have contributed to this convergence of ABR and neur al thresholds. First, our results suggest that the elevation of the most se nsitive neural responses led to a compressed threshold distribution. Conseq uently, only a narrow range of sound levels separated stimulus conditions t hat activated relatively few fibers from those that were sufficient to evok e a robust population response. In addition, the threshold responses of imp aired auditory nerve fibers may have been augmented by activity in the more sensitive 'off-frequency' regions that surrounded a discrete cochlear lesi on. Across varying degrees of hearing loss, the ABR maintained a systematic relationship to auditory nerve fiber thresholds, and therefore has the pot ential to be used as a functional assay of cochlear pathology, (C) 2001 Els evier Science B.V. All rights reserved.