VISUAL PONTOCEREBELLAR PROJECTIONS IN THE MACAQUE

The cerebellum plays an important role in the visual guidance of movem ent. In order to understand the anatomical basis of visuomotor control , we studied the projection of pontine visual cells onto the cerebella r cortex of monkeys. Wheat germ agglutinin horseradish peroxidase was injected into the dorsolateral pens of two monkeys. Retrogradely label led cells were mapped in the cerebral cortex and superior colliculus, and orthogradely labelled fibers in the cerebellar cortex. The largest number of retrogradely labelled cells in the cerebral cortex was in a group of medial extrastriate visual areas. The major cerebellar targe t of these dorsolateral pontine cells is the dorsal paraflocculus. The re is a weaker projection to the uvula, paramedian lobe, and Crus II, and a sparse but definite projection to the ventral paraflocculus. The re are virtually no projections to the flocculus. There are sparse ips ilateral pontocerebellar projections to these same regions of cerebell ar cortex. In nine monkeys, we made small injections of the tracer int o the cerebellar cortex and studied the location of retrogradely fille d cells in the pontine nuclei and inferior olive. Injections into the dorsal paraflocculus or rostral folia of the uvula retrogradely labell ed large numbers of cells in the dorsolateral region of the contralate ral pontine nuclei. Labelled cells were found ipsilaterally, but in re duced numbers. Injections outside of these areas in ventral parafloccu lus or paramedian lobule labelled far fewer cells in this region of th e pens. We conclude that the principal source of cerebral cortical vis ual information arises from a medial group of extrastriate visual area s and is relayed through cells in the dorsolateral pontine nuclei. The principal target of pontine visual cells is the dorsal paraflocculus. (C) 1994 Wiley-Liss, Inc.