Electrophysiological correlates of the response decrement produced by mechanical stimuli in the protozoan, Stentor coeruleus.

The response pattern of Stentor coeruleus has been studied using repetitive mechanical stimuli which were applied to a limited body surface. The decrement in the probability of response was found to parallel that previously reported when more gross mechanical stimuli were employed, This result justified the employment of such localized stimuli in the determina tion of elec trophysiological correlates of the response decrement. Electrophysiological records show a decrease in the amplitude of the prepotential and an increase in the latency of the response during the course of repetitive stimulation. After considering possible complications resultant from changes in the amplitude of the diphasic potential and the relation of the stimulus probe to the animal, it was concluded that the potential changes noted do, in fact, indicate a change in receptor function is associated with the response decrement. This result was predicted on the basis of previously reported behavioral data.