Emergence of temporal-pattern sensitive neurons in the midbrain of weakly electric fish Gymnarchus niloticus.

Sensitivity of neurons in the torus semicircularis of a weakly electric fish, Gymnarchus niloticus, to two stimulus parameters that are critical for its behavior the jamming avoidance response was examined. The first parameter is the sign of frequency difference between discharge frequencies of fish's own electric organ and that of a neighbor's. The second parameter is the spatial orientation of neighbor's electric field. Whereas neuronal ambiguity of frequency coding for different orientations of neighbor's electric field is predicted, unambiguous JAR occurs at the behavioral level. Most neurons in the torus semicircularis showed sensitivity to the sign of frequency difference. Although a small number of neurons showed preference to a consistent sign of the frequency difference, the coding of the sign of frequency differences was found to be ambiguous with a highly variable pattern of responses for different orientations in most of neurons.