Information Processing in the Electrosensory System

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Processing of complex sensory information to generate behavior is a major function of the brain, and one very useful model system for studying this integration has been the brain of weakly electric fish. These fish generate a repetitive weak electrical signal from special organs, and detect the electric field around them by specialized electroreceptors all over the body. The signal is used for social communication and for spatial "electrolocation" in much the way bats or dolphins use echolocation to identify and locate objects. A population of electric fish has the same problem as a city with multiple radio stations: if the signals used by two separate individuals are too close together in frequency, each one effectively "jams" the signal reception of the other. Some electric fish that use highly regular signals have overcome this problem by a behavior called the "jamming-avoidance response" (JAR); the fish with the slightly higher frequency moves its emission frequency up just a bit, and the fish with the slightly lower frequency moves its frequency down just a bit, to widen the separation and so help each fish to identify of its own signal against the background environment of other fish. This behavior requires the fish to recognize not only that the jamming signal is present, but whether its own signal is higher or lower in frequency than the jamming signal. Recently it has been found that some species of electric fish in Africa, not at all closely related to the better-studied South African electric fish species, have the same JAR behavior, but apparently produce it by a different circuit in the brain. This project uses physiological and anatomical techniques of recording and tracing the connections of single nerve cells in the brain to clarify how this response is controlled by the brain in the African fish. Particular emphasis will be on the spatial and temporal patterns of two sensory cues, known as amplitude modulation and differential phase modulation, which both are essen tial for the behavior. The results will be important for understanding mechanisms for the independent evolution of similar adaptive behaviors, and also will be important to understanding general principles of brain organization related to sensory behavior in such systems as vision and hearing.