The climbing fiber projection to the flocculus and adjacent paraflocculus in the cat

The olivo-cerebellar projection to the flocculus and adjacent parts of the ventral paraflocculus was investigated by means of anterograde transport of tritiated leucine. Four subdivisions of the principal olive (caudal lateral bend, ventro-lateral outgrowth, rostral and caudal dorsal cap) and the rostral tip of the medial accessory olive were involved in the projection. In the flocculus contralateral to the injection site, eight different climbing fiber strips are distinguished, most of which extend into the most caudal lobule of the ventral paraflocculus and the area of cortex connecting it with the flocculus. One of these, present in the extreme caudal edge of the area under study, originated from the rostral part of the medial accessory olive and was labeled C2. The others originate in the principal olive and are labeled F-strips. Whereas the caudal lateral bend is connected with a single strip (F7), the remaining subdivisions give origin to two separated strips. The ventro-lateral outgrowth, the rostral and caudal dorsal cap are the respective sites of origin of the strips F2 + F5, F3 + F6 and F1 + F4. The significance of the strips is discussed in relation to the cerebellar relay nuclei, known to receive floccular efferents. A new nomenclature is proposed for the lobular subdivision of the flocculus and adjacent parts of the ventral paraflocculus, together with a simple method for the construction of a two-dimensional diagram of these areas.