Zonal organization within the projection from the inferior olive to the rostral paramedian lobule of the cat cerebellum.

The projection from the inferior olivary nucleus to the forelimb-related regions of the c1, c2 and c3 zones within rostral folia of the paramedian lobule of the cat cerebellum was studied using a combined electrophysiological and neuroanatomical tracing technique. In each experiment, the cerebellar cortical zones were identified by their receipt of spino-olivocerebellar input evoked by percutaneous electrical stimulation of the limbs. A small (15-30 nl) injection of wheatgerm agglutinin-horseradish peroxidase (WGA-HRP) was then made into the centre of one of the zones. The olivary regions projecting to each zone were compared with the regions within the olive that have previously been shown to project to the corresponding cortical zones within lobule V of the anterior lobe. The results show that some (but not all) of the paravermal zones in the anterior lobe are also represented in the paramedian lobule (PML). The most medial (c1) zone in rostral PML receives climbing fibre input from an area in the rostral dorsal accessory olive which overlaps partially with the area that projects to the medial half of the c1 zone in lobule V. A zone equivalent to the lateral half of the c1 zone (the cx zone) in lobule V does not appear to be present within rostral PML. A middle (c2) zone within rostral PML receives olivary input from a region within the rostral medial accessory olive that overlaps partially with the area that projects to the c2 zone in lobule V. The presence of a c3 zone within rostral PML was found to be variable between animals and it could be identified electrophysiologically in only two out of a possible nine cases. In summary, the results demonstrate that, although a number of similarities exist between the olivocerebellar projections to corresponding cortical zones in the two forelimb-receiving regions of the cat paravermal cortex, the differences in olivocerebellar connectivity between the two regions suggest that functional differences between them may also exist.