The olivocerebellar projection studied with the method of retrograde axonal transport of horseradish peroxidase. V. The projections to the flocculonodular lobe and the paraflocculus in the rabbit.

HRP was injected in the flocculonodular lobe and the paraflocculus in the rabbit to determine the areas of the inferior olive which project onto these cerebellar regions. Following injections in the flocculus labeled cells occurred in the dorsal cap and the rostralmost tip of the medial accessory olive. Following injections in the nodulus labeled cells were likewise found in the dorsal cap, but in addition in the rostralmost part of the dorsomedial cell column and the adjoining part of the medial accessory olive. Injections in the dorsal paraflocculus gave rise to labeling in the rostrolateral part of the medial accessory olive, while injections in the ventral paraflocculus resulted in labeling in the principal olive, mainly in the lateral part of the ventral lamella. Injections in the lateral third of the dentate nucleus gave rise to labeling mainly in the dorsal lamella of the principal olive. The results are discussed with reference to those obtained by previous authors. There are both similarities and discrepancies. It appears from what is known of afferents from areas mediating visual impulses to the inferior olive that the olivary areas projecting onto the flocculonodular lobe, and possibly the dorsal paraflocculus, may mediate visual impulses to these lobules.