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 inv estigated the way information received by the lateral line is processe d by neurons in the hindbrain of two fish species, the bottom dwelling catfish, Ancistrus sp., and the goldfish, Carassius auratus. We stimu lated the lateral line with a small object moving in the water and rec orded the responses of single units in the medulla. Medullary lateral line units increased their discharge rate when the moving object passe d the fish. At least three different response types could be distingui shed on the basis of response patterns. In some units, the response pa ttern differed for different motion directions, indicating that these units were sensitive for the direction of object motion. In general, d ischarge rates decreased both when object speed decreased or when obje ct distance increased. The results suggest that in the hindbrain of fi shes different neuron populations maybe responsible for the processing of different aspects of hydrodynamic stimuli.