Auditory responses from the saccule: further evidence for the mechanical origin of inhibition

Abstract

Action potentials were recorded from single fibers from the saccule in the American toad (Bufo americanus). While some of the fibers respond only to substrate vibration, many others are sensitive to airborne sound. The response of a fiber to an excitatory tone can be totally inhibited by a second higher-frequency tone. Furthermore, each fiber can be excited by a pair of tones with a frequency difference approximately equal to the unit's best excitatory frequency. These saccular fiber responses are very similar to those of the inhibitable fibers from the amphibian papilla. Our previous studies of the amphibian papilla have demonstrated that inhibition and difference tone excitation are related phenomena having a mechanical rather than a neural origin. That these two organs, so structurally different, should exhibit such similar response properties indicates that inhibition and difference tone excitation do not occur in the organs themselves, but rather in the fluids of the inner ear or in the middle ear. [Supported by NIH Grant NS-09244.]