Lateral-Line Input and Stimulus Localization in the African Clawed Toad Xenopus SP

Abstract

1. Intact Xenopus sp. responded to a train of surface waves with a single, stimulus-directed motor response which consisted of a turning component and a displacement component. The turning angle increased in a linear fashion with the stimulus angle. 2. The magnitude of the turning angle was not affected by (a) the size of the animal, (b) the way the surface wave was elicited (with a drop of water or by dipping a rod into the water), (c) reflected waves and (d) the number of successively administered stimuli. 3. With no lateral-line organs left intact Xenopus could still localize the origin of a surface wave, but with reduced accuracy. 4. With only two stitches left intact on the left and on the right occipital lines, the turning angles were more widely scattered for stimuli placed at angles larger than 90°. The scatter was even larger than that of the equivalent responses from animals without a functional lateral-line system, i.e. the directional responsiveness in the partly lesioned animals was less accurate than in those with their entire lateral-line inoperative. 5. Xenopus with four or two ipsilateral occipital stitches left intact were no longer able to orientate accurately. When the animal was stimulated on the lesioned side it frequently turned to the wrong side. These errors were absent or less frequent when the animal was stimulated on the intact side. 6. The lesion experiments indicated that (a) a few organs provide sufficient information for an appropriate turning response, but the turnings were only roughly directed towards the stimulus, and (b) the decision whether Xenopus localizes a stimulus on the left or right side depends on whether the central nervous system receives information from one or both sides.