Modification of responses from specific sensory systems in midbrain by cerebellar stimulation: experiments on a teleost fish.

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Abstract
The effects of cerebellar stimulation on evoked potentials and/or unit responses of different structures of the afferent pathways, for several sensory modalities, were investigated in curarized catfish (Ictalurus nebulosus). Sensory stimulation consisted of flashes for the visual system and clicks, electric pulses, water jets and table tapping for the octavolateralis system. Afferent responses were recorded from optic tectum and torus semicircularis for the optic system and octavolateralis system, respectively, and displayed as slow-wave averages and poststimulus time histograms of spikes. A train of stimulus pulses was delivered to various parts of the cerebellum at intervals before the sensory stimulation. The effects of such stimulation at suitable sites and intervals were an enhancement of the optic evoked response and a decrease of the octavolateral responses. The most effective sites of cerebellar stimulation are the areas said to be receptive for the modality concerned. Sensory responses recorded at the medullary level were not affected by cerebellar stimulation. Peripheral inhibition can be ruled out, for some of the modalities studied, by the blockage of lateral line efferents by curarization, the absence of efferents on electroreceptors, and the lack of action of the cerebellar stimulation on the electroretinogram. A central modulatory action on the afferent responses in the midbrain mediated by the cerebellum was indicated.

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