Longitudinal and topographical organization of the olivary projection to the cat ansiform lobule.

This study on the organization of the olivary projections to the ansiform lobule in the cat was aimed at defining the longitudinal zonal pattern and the internal topography within the zones. The horseradish peroxidase method was used. Two types of injections were made: large injections covering the full extent of small groups of folia, and small injections aimed to be restricted to the single zones proposed by Voogd. It was shown that olivary projections to these parts of the cerebellum originate from the dorsal and medial accessory nuclei and from the principal nucleus, in agreement with previous studies. Moreover it was found that the ventral lamella and the dorsal lamella (and bend) of the principal nucleus give rise to two distinct, non-overlapping, cerebellar projections to D1 and D2 zones, respectively. It is thus concluded that in the cat four separate olivo-cerebellar strips, corresponding to the C2, C3, D1 and D2 zones of Voogd, are present in the ansiform lobule. In addition a transverse rostro-caudal organization was found, in which discrete regions of each olivary subdivision are connected to discrete areas of the crural cortex, within each olivo-cerebellar strip. The old idea of a point-to-point topography in the olivo-cerebellar system is consequently still valid, being compatible with the now proven longitudinal zonal pattern of the olivo-ansiform projection. The fact that the two subdivisions of the principal olive, here shown to project to separate D1 and D2 zones of the ansiform lobule, receive specific sets of afferents suggests that the two cortical zones are part of two different cerebellar operational units.