Stimulus Localization in Xenopus: Role of Directional Sensitivity of Lateral Line Stitches

Since the experiments of Kramer (1933) and Dijkgraaf (1947), it has been known that the clawed toad (Xenopus sp.) can localize moving objects in water or on the water surface. Kramer demonstrated that the lateral line system was responsible for the toad’s ability to turn toward the source of disturbance. Ablation of all lateral line stitches on one side of the animal abolished its response to a hand-held vibrating sphere and to a weak water current delivered by a pipette on the side. Responses to stimuli delivered on the intact side remained unaffected. Dijkgraaf has investigated the reactions of the toad to surface waves created by dipping a small rod into the water. The toad responded by turning toward the wave center even when it rested on the substrate, 10 cm below the water surface. As it turned out, surface waves are well suited for a detailed study of lateral line function in Xenopus, since they elicit unconditioned orienting responses which do not habituate over the course of more than 140 successive stimulations (Gorner 1976).