A role of burst firings of hindbrain neurons in detecting object distance in electrolocation

Weakly electric fish generates electric field around its body using electric organ discharge and can accurately detect the location of an object using the modulation of electric field induced by an object. Objects with electric properties different from those of the surrounding water distort the electric field around fish´s body depending on the size, distance and electric properties of objects. It is not clear yet how the fish recognizes the properties of an object such as its electric property, location and size based on its electric image. As the first step to clarify the neuronal mechanism of electrolocation, we developed a model of fish body by which we describe numerically the spatio-temporal patterns of electric field around the fish body. We made also neural models of electroreceptors distributed on the fish body and of electrosensory lateral line lobe (ELL) to investigate what kinds of information of electric field distorted by an object they detect. The models reproduce qualitatively the experimental results about the detections of size, distance, and moving directions of an object. We show that the lateral distance between a moving object and fish is encoded by the synchronous burst firing of ELL neurons, reflecting the spatio-temporal correlations of EOD stimuli received by the receptors.