An experimental study on cupular function: mapping of the cupula by direct stimulation.

In the present study, the posterior semicircular canal of the frog was isolated and the entire cupula was exposed after cutting the ampullary wall. The surfaces of the utricle and the lateral cupula were depressed by a fine glass pipette. Action potentials were taken from the posterior ampullary nerve and were compared by using nine points of stimulation on the cupular surface of the utricular side and two points on the lateral surface. The maximum action potential was recorded at stimulus to the lowest point on the utricular side surface. This potential proportionally decreased as the stimulation point approached the top of the cupula. Depression of the lateral surface evoked only a small potential. In contrast to the stimulus applied to the utricular surface, a stimulus to the upper point of the lateral surface yielded a greater potential than did a stimulus to the lower point.