Single-neuron labeling and chronic cochlear pathology. IV. Stereocilia damage and alterations in rate- and phase-level functions.
The rate and phase of auditory-nerve response to tone bursts were studied as a function of stimulus level in normal and acoustically traumatized animals. The rate- and phase-level functions of normal auditory-nerve fibers are often separable into a low-intensity component (component I) and high-intensity component (component II), as defined by a dip in the rate function and a simultaneous abrupt shift in the phase function at stimulus levels near 90 dB SPL [10,12,9]. Baseline data are established by defining the relation between stimulus frequency and the characteristic frequency and spontaneous discharge rate of a fiber normally required for the appearance of these two components in the response. Abnormalities of the level functions are shown to occur in acoustically traumatized ears. Noise-induced threshold shift is often characterized by selective attenuation of component I. In some instances, it appears that component I has been eliminated, leaving a response which is identical in threshold, phase and maximum discharge rate to a normal component II. Results of single-unit labeling in such a case suggest that the selective attenuation of component I is associated with selective loss of the tallest row of stereocilia on the inner hair cells (IHCs). It is suggested that component I is normally generated through an interaction between the outer hair cells and the tall row of IHC stereocilia, while component II requires only the shorter row of IHC stereocilia.
D000818:Animals; D002415:Cats; D002923:Cilia / Q000502:physiology; D003055:Cochlear Microphonic Potentials; D006198:Hair Cells, Auditory / Q000503:physiopathology*; D006199:Hair Cells, Auditory, Inner / Q000503:physiopathology; D006317:Hearing Loss, Noise-Induced / Q000503:physiopathology*; D008144:Loudness Perception / Q000502:physiology*; D009412:Nerve Fibers / Q000502:physiology; D010898:Pitch Perception / Q000502:physiology*; D000159:Vestibulocochlear Nerve / Q000503:physiopathology*