Water Wave Analysis with the Lateral-Line System

Abstract

The organization of water surface wave analysis with the lateral-line system has been investigated by electrophysiological recording and behavioral testing in the clawed frog, Xenopus laevis. In the afferent fibers, wave frequency is encoded by phase coupling of the discharges, while stimulus intensity is encoded over a range of 80 dB by phase coupling and mean firing rate. Additionally, cardioid directional sensitivity is found. Behavioral tests after partial lesions show that small groups of the animal’s lateral-line organs are sufficient for localizing waves from any direction; this suggests that the high number of lateral-line organs in Xenopus may serve more complex wave analyses. The capability for complex analysis is demonstrated in the animal’s ability to detect the direction and the frequency of component waves in wave superpositions. In the midbrain, a topological organization with regard to wave direction is found that does not reflect the topology of the organs on the body. Wave frequency discrimination is found: its accuracy is comparable to that in hearing, and wave frequency memory is of absolute pitch quality. The results correspond to stimulus processing in the auditory system and give new support to the octavolateralis hypothesis of a common evolutionary origin of the lateral-line and eighth-nerve sensory systems.