The fine topography of climbing fiber projections to the paramedian lobule of the cerebellum in the cat

Motor cortex and somatosensory afferents of climbing fibers (CFs) which terminate in the two rostral folia of the paramedian lobule of the cerebellum were studied in pentobarbital-anesthetized cats. CF responses were elicited in all but one Purkinje cell recorded within the paramedian lobule by stimulation of one or more pericruciate sites; 67% of these also had a peripheral receptive field or were excited by stimulation of the superior radial, sciatic, or infraorbital nerve. CFs responded to stimulation of peripheral nerves at either short latency (14 to 34 ms) or long latency (<120 ms), or gave a mixture of both responses. Those responding at long latency generally did not have peripheral receptive fields. The forelimb was predominantly represented in folia a and b, although it was noted that the relationship between bodily representation and surface landmarks was variable between cats. The proximal portion of the limb was represented medially and the distal part laterally. A clear relation was established between the location of the lowest-threshold cortical site and the peripheral afferents which evoked a CF response in any given cell. The cortical site was generally in a region controlling movements of the body parts on which the peripheral receptive field was found. Two populations of CFs exist in this region, one receiving convergent and complementary cortical and peripheral information and another which, under the present experimental conditions, is excited only from the cortex. It is suggested that these two populations may project as interdigitating bands which run across the long axis of the folia.