Absence of tonotopic organization in the motion of the basilar membrane of the alligator lizard

Abstract

In the alligator lizard it appears that auditory nerve fibers from the apical end of the receptor organ have low characteristic frequencies (0.2 < CF < 0.8 kHz) and those from the basal end have high CF's (0.9 < CF < 4.0 kHz). [Weiss, Mulroy, Turner, Pike, Brain Res. 115, 71–90 ( 1976)]. We have used the Mössbauer method to measure velocities of radioactive sources on the basilar membrane. Control experiments indicate that (1) placement of Mössbauer source need not alter the response properties of the ear, and (2) the source sticks to the basilar membrane. For the velocity levels we have used, the motion appears to be independent of the longitudinal position of the Mössbauer source on the basilar membrane. The frequency dependence of basilar membrane velocity is similar to that of the columella (stapes) velocity. These results indicate that the frequency selective properties of the auditory nerve fibers are strongly influenced by mechanisms other than basilar membrane motion. [Work supported by NIH.]