Electrosensory input to the corpus cerebelli of the high frequency electric fishEigenmannia virescens

Summary

• 1. Evoked potentials as well as single unit responses show that the caudal lobe of the cerebellum ofEigenmannia receives input via the electro-sensory system. Many of the responding cells had properties similar to those typical of Purkinje cells. The cells probably receive input from specific receptive fields, however precise localization of these fields was not achieved.

• 2. Graded deformations of the electric field produced by the fish as well as artificial fields applied around a fish whose electric organ was silenced caused graded responses in the cerebellum. Responses to both stimulus types were usually phasic with a time constant of decay of about 3.5 sec, increases as well decreases in firing frequency were observed. The latency of the neural responses decreased as stimulus strength increased, ca. 20 msec being the shortest latency observed.

• 3. The minimum voltage gradient necessary to cause a change in the firing frequency of a cerebellar cell was about 100 μV/cm, for a fish whose electric organ was silenced, and the changes in spike frequency were approximately linearly related to the logarithm of the stimulus intensity. The neurons responded best to stimuli having a frequency near to what the fish's electric organ discharge frequency would have been. All cells seen within an individual responded best to this same frequency, but the frequency preferences between individuals varied according to the discharge frequencies of the individuals.

• 4. Units were encountered in the same brain area which responded to passive changes in the position of the tail in the electrically silent fish, these have tentatively been categorized as proprioceptors. A number of these cells also responded in a typical way to electrosensory input giving a population of cerebellar neurons with a bimodal input.