An experimental study on the physiological significance of the mode of cupular movement

Isolated frog posterior semicircular canals were used. The ampullary nerve action potentials were recorded under three kinds of cupular movement, i.e., swing-door deflection, "cupula fixation-1" and "cupula fixation-2". Cupula fixation-1 was achieved by immobilizing the central top portion of the cupula, while cupula fixation-2 was achieved by immobilizing the entire top of the cupula. Cupula fixation-1 resulted in action potentials which were comparable to those of the swing-door deflection in terms of the maximum spike count and the stimulus-response curve. Cupula fixation-2 resulted in potentials with the maximum spike count comparable to the swing-door deflection; however, the response increase rate was very low. The time courses of the potentials in those cases of cupula fixation-1 and -2 were extremely short (about 2-3s) when compared to that of the swing-door deflection. These findings suggest that the swing-door deflection is physiologically more relevant in giving the optimum increase in response rate, as well as maintaining the time course of the tonic response.