Abstract:

Auditory electrophysiological experiments were conducted to study the hypothesis that sound transduction by frogs is dependent on the volume of a resonant cavity, which is made up of the middle ear, Eustachian tube, and mouth. Using a closed acoustic delivery system, the extracellular responses to the interaction of a 100-ms pure tone of varying frequency and a single-cycle sinusoidal pulse were recorded from the eighth-nerve, via a ventral approach. Results show that the resonant cavity system used in vocalizing is also involved in sound transduction. When the Eustachian tube is closed, by a small piece of oiled paper or Apiezon, there is a reduction in the mean spike count of the eighth-nerve fibers. Removing the occlusion restores the firing rate to normal levels. This information, together with knowledge of the fibers' best excitatory frequency (BEF) and inhibitability, is important because it provides insight into the peripheral origin (i.e., Amphibian papilla, Basilar papilla, or Sacculus) of the nerve fibers. Since some nerve fibers respond by phase locking to the stimulus, taking the FFT of the response also improves our understanding of sound transduction methods employed by the inner ear apparatus. [Work supported by NIH predoctoral fellowship GM17890 to MA.]