Integration of hydrodynamic information in the hindbrain of fishes

Fishes detect weak water movements generated by a predator or by prey with the aid of the mechanosensory lateral line. In this study, we investigated the way information received by the lateral line is processed by neurons in the hindbrain of two fish species, the bottom dwelling catfish, Ancistrus sp., and the goldfish, Carassius auratus. We stimulated the lateral line with a small object moving in the water and recorded the responses of single units in the medulla. Medullary lateral line units increased their discharge rate when the moving object passed the fish. At least three different response types could be distinguished on the basis of response patterns. In some units, the response pattern differed for different motion directions, indicating that these units were sensitive for the direction of object motion. In general, discharge rates decreased both when object speed decreased or when object distance increased. The results suggest that in the hindbrain of fishes different neuron populations maybe responsible for the processing of different aspects of hydrodynamic stimuli.