Perception of the Electric Organ Discharge of Conspecifics by a Weakly Electric Fish

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Scientists have long been interested in understanding the neural processes underlying perception. In humans, these processes and the sensory stimuli themselves are often so complicated that a complete understanding of the perceptual process is elusive. Much progress has been made, however, with simpler animal models in which (1) the sensory stimulus in question is easily quantifiable and can be manipulated, (2) there is a way to tell if the animal can detect the stimulus, and (3) the response properties of the neurons responsible for the perception can be measured directly. Electric fish provide such a model system. Dr. Zakon's research involves a species of fish that continuously produces a weak electric field from an organ in its tail. This field (the electric organ discharge, or EOD) surrounds the fish's body. The animal is able to navigate and localize objects in dark, murky water by detecting distortions in the electric field with specialized electroreceptors on the body surface. The EOD is also used extensively in communication between fish. The EOD voltage varies in a nearly sinusoidal fashion. The EOD frequency of each individual is unique, and that of males and females differs by roughly an octave. The electroreceptors are tuned to the fish's own EOD frequency and are much less sensitive to other frequencies. How, then, does the fish perceive the EODs produced by members of the opposite sex? When two electric fish are close to each other, each fish's electroreceptors are stimulated by a signal that is the sum of the two EODs. This interaction of EOD signals probably allows the fish to detect each other's EODs. Using behavioral training and neurophysiological recording techniques, Dr. Zakon is studying how these summed EOD signals are perceived and how information about the presence of another fish is extracted from this signal. Dr. Zakon's research is elucidating the perception and analysis of a biologically relevant stimulus. This understanding can be gained because electric fish often rely on electrical signals for the detection of other members of the species and because electrical signals are easy to measure and manipulate. The underlying processes of signal analysis elucidated should be useful in understanding perceptual systems in other vertebrates.