How lesioning the nucleus praeeminentialis affects electrolocation behavior in the weakly electric fish, Apteronotus leptorhynchus.

The ability to orient to and track moving electrolocation targets was assessed in normal Apteronotus leptorhynchus and in those with unilateral lesions of the nucleus praeeminentialis dorsalis. 1. Each fish was trained to hover between two vertical metal rods and track their movement. Two aspects of this behavior were measured: a) the hovering position of the fish relative to stationary rods; b) the latency between the onset of rod motion and the fish's tracking response. Control fish hovered midway between stationary rods, while lesioned fish hovered closer to the rod ipsilateral to the lesion. Response latency varied negatively with rod diameter in both sets of fish, and lesioned fish exhibited shorter latencies than control fish. While the response latencies of control fish were shortest when their starting position was midway between the rods, lesioned animals latencies were shortest when they hovered closer to the rod ipsilateral to their lesion. 2. Control fish responded to the approach of a single metal ball to either side of the body with nearly equal latencies and fish-to-object distances. After lesioning, response latency increased and fish-to-object distance decreased for approaches to the side ipsilateral to the lesion; opposite changes occurred for contralateral approaches.