Differences in the CF dependence of response phase of gerbil and guinea pig auditory nerve fibers

Abstract

Time‐locked responses of auditory nerve fibers to acoustic sinusoids having frequencies between 100 and 400 Hz were studied in gerbils and guinea pigs. With the exception of the responses of gerbil fibers with CFs above 10 kHz, which produce double‐peaked histograms, the responses of most fibers in both species produce single‐peaked histograms when the modulation of spontaneous activity is less than 100%. Within this restricted modulation range, the preferred phase of response is relatively independent of stimulus amplitude. Nonetheless, the variation of the response phase with CF is fundamentally different in the two species. Whereas gerbil fibers show an abrupt 180° phase transition in the CF range between 2 and 4 kHz, the response phase of guinea pig fibers is CF‐independent for stimulus frequencies that are at least 12 octave below fiber CF. The finding of different phase functions in the two species indicates that caution should be exercised in basing models of the neural excitation process in the cochlea solely on data obtained from one mammalian species.