Localization of Electric Communication Signals

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Sense organs provide two parallel important functions. They serve to detect and recognize particular stimuli, and to localize a stimulus in space; the animal then can make appropriate behavioral responses with a correct spatial orientation to the guided behavior. Electroreception is a special sense exploited by several fishes that use electric organs to produce a discharge used for object detection and communication. Unlike propagated sound that gives timing cues for auditory localization, electric signals act instantly; unlike straight rays of light that give sight lines for visual localization, the vectors of the electric currents are often curved. This project examines the guidance of oriented electrosen- sory behavior in electric fish using behavior, physiology, and computer modelling. Video analysis in three dimensions will be used to quantify the swimming path as a fish orients to distant electric discharges that mimic other electric fish. This behavior involves aligning the body axis parallel to the electric field vector, and swimming toward the current source. The approach track will be correlated with the electric field derived by computation that will include aquarium geometry, and both stationary and moving electrodes. Electrophysiological activity will be recorded from the nerves that innervate two classes of electroreceptors, to characterize the sensory coding of the electric field parameters. The physiological results will be compared to theoretical analyses of the electric field across the fish's skin, as a function of geometry and skin resistance. Mechanisms of stimulus localization are fundamental to sensory processing. This study uses a novel approach that will provide a substantial contribution to understanding electrosense in particular, and other sensory systems in general.