Visual and visual-vestibular responses of frog cerebellar neurons

Abstract

Micropipette recordings were obtained from single neurons of the frog cerebellum to monocular and binocular visual stimuli. 64% of the visually activated cerebellar neurons could be identified as Purkinje cells. Two major groups of cerebellar visual neurons could be distinguished: The neurons of the first group have restricted receptive fields within the visual field of one or both eyes and respond to diffuse illumination or to small contrast stimuli moving through the receptive field. The neurons of the second group have no restricted receptive fields and respond best to a moving patterned surround, stimulating one or both eyes. Among these neurons four classes could be distinguished by binocular surround stimulation: Neurons activated by horizontal movement to the right (C1 neurons), neurons activated by movement to the left (C2 neurons), neurons activated by movement in both directions (C3 neurons) and neurons which are inhibited by movement in both directions (C4 neurons). The contribution of each eye to the binocular response revealed that the signals from both retinae interact either in a Homodirectional or a Heterodirectional manner. Stimulation of the receptors in the horizontal semicircular canal (horizontal turning movement) leads to a change in the activity of cerebellar visual neurons. Depending on the directionality of the neurons, an enhancement or a reduction in the neuronal activity can be achieved by combining visual and vestibular stimulation. Electrical optic nerve stimulation revealed two latency ranges for the activation elicited by the mossy fiber as well as by the climbing fiber system.