Deficit in object detection (electrolocation) following interruption of cerebellar function in the weakly electric fish,Apteronotus albifrons

Neural units in the cerebella of electrosensitive gymnotid fish respond to objects which distort the fish's electric field 1-4. Those data suggest that in the cerebellum there is processing of afferent information relevant to object detection (electrolocation)S, 12,1~ mediated by the electrosensory system. The lesion and cold-block experiments described here test the hypothesis that the cerebellum plays an important role in object detection. Specimens, Apteronotus albifrons (Apteronotidae, Gymnotoidei) were bilaterally enucleated under tricaine methanesulfonate anesthesia at least 4 days prior to experimentation. Potentials associated with opercular and jaw excursions were recorded between a stainless steel wire electrode implanted in the musculature which controls the ventilation movements, and a second electrode in the water. The fish was held securely in a nylon mesh net in the center of a 27 cm × 121 cm × 27 cm aquarium filled with water adjusted to 2 K~Q. cm resistivity. Amplified signals were filtered (0 30 Hz pass band), displayed visually, and recorded with a polygraph. Plexiglas or aluminum objects which were mechanically moved anterior to posterior, parallel to the fish, elicited a reduction in frequency and amglitude of the opercular potentials (Fig. l). For data analysis only changes in fiequency were counted. The magnitude of this 'ventilation response' is a function of object distance (see Fig. 2A, solid dots, r . . . . 1, P -0.05, Spearman Rank Correlation Coefficient). In two control experiments electrically transparent agar rods (Kalmijn, personal communication) failed to elicit consistent ventilation responses while the same fish responded reliably to similar Plexiglas rods. These controls and the fact that the fish were blinded indicate that the ventilation response is mediated by the electrosensory system. In the first experimental series 4 specimens, pre-selected on the basis of having