Stages of degradation of timing information in the cochlea: a comparison of hair-cell and nerve-fiber responses in the alligator lizard.

Responses to clicks and tone bursts of hair cells and nerve fibers in the free-standing region of the alligator lizard cochlea were compared. The objective was to determine the extent to which the hair-cell processes that produce the receptor potential are also responsible for the attenuation of the synchronized responses of nerve fibers. The AC component of the receptor potential of these hair cells has a high-frequency attenuation of 20 dB/decade [Holton and Weiss (1983) J. Physiol. 345, 205-240], whereas the synchronized response of cochlear neurons is attenuated at a rate of least 80 dB/decade [Rose and Weiss (1988) Hear. Res. 33, 151-166]. Therefore, the processes that link the receptor potential to the nerve discharge act as a lowpass filter with a high-frequency attenuation of at least 60 dB/decade. This could be obtained from a cascade of at least three first-order lowpass filter processes.