Latency of Whole-Nerve Action Potentials: Influence of Hair-Cell Normalcy

An experimental hypothesis was derived based on the findings of the clinical simultaneous binaural median plane lateralization test and the literature review of the latency of action potentials (AP). It states that the latency of action potentials as a function of absolute signal intensity (SPL) in cochleae with different degrees of hair-cell losses is identical to that in normal cochleae at suprathreshold levels for signals with a given spectral content and a fixed rise time. The pathological cochleae were created by injections of kanamycin in guinea pigs and were monitored histopathologically, utilizing the surface preparation technique. The results show that the latency of AP as a function of SPL remains constant regardless of the pattern and degree of hair-cell loss in the cochlea, and they consequently prove that the hypothesis of this experiment cannot be rejected. For a signal with a given frequency and a fixed rise time, the latency of the onset AP apparently depends only on the magnitude of the displacement of the basilar membrane regardless of the overall magnitudes of CM or AP.