Electrophysiological study on colliculo-cerebellar pathway in cat.

The retino-colliculo-cerebellar and visual cortical-cerebellar pathways were reexamined by means of latency measurement of evoked potentials on 50 immobilized cats. I. The vermian cerebellar response to optic nerve stimulation was a large positive wave sometimes superimposed by small waves in the decay phase. The positive wave was considered to originate from the mossy fiber system, based on the results obtained from the relation of this wave to evoked spike responses recorded from the deeper layers. 2. The latencies of cerebellar, collicular and visual cortical responses to optic nerve stimulation were 6.3-7.5, 3.5-4.0, and 5.3-7.3 msec, respectively. The latency of the cerebellar response to visual cortical stimulation was 6.0-6.9 msec, while that of the collicular response to visual cortical stimulation was 1.5-2.0 msec. 3. Two positive waves (C 1 and C2 ) were evoked in the cerebellum by superior colIiculus stimulation. The latencies of these waves were 1.5-2.5 and 3.5-4.3 msec, respectively. C\ was evoked by stimulation of any layer of the superior colliculus, while C2 was evoked by stimulation of only the optic and intermediate layers. A striking property of C2 was its very delayed recovery, in contrast to C\ . The present results indicate that C\ has a definite relation to the retino-colliculocerebellar route and C2 related to the route from visual cortex to cerebellum, and lead us to reconfirm that the main pathway carrying visual information to the cerebellum was relayed at the superior colliculus.