Timing of neural excitation in relation to basilar membrane motion in the basal region of the guinea pig cochlea during the presentation of low-frequency acoustic stimulation.

In spite of many studies concerning auditory nerve action potentials, the timing of neural excitation in relation to basilar membrane (BM) motion is still not well understood. In this study, therefore, BM vibrations in the basal region of the guinea pig cochlea were measured using a laser Doppler velocimeter, and action potentials in auditory nerve fibers were recorded by a conventional microelectrode technique. An attempt was then made to determine the relationship between BM motion and neural excitation in auditory nerve fibers. To obtain BM responses in the high-characteristic frequency (CF) region (18-22 kHz) and responses of auditory nerve fibers with high CFs (14-22 kHz), low-frequency stimuli (50-2000 Hz), frequencies of which were well below CFs, were presented at 60-100 dB SPL. The results indicated that neural excitation occurred when the BM was displaced toward the scala vestibuli. Moreover, the neural excitatory phase did not significantly vary with the fiber's CF between 14 and 22 kHz nor with the stimulus level between 60 and 100 dB SPL.