Topographic features of climbing fiber input in the rostral vermal cortex of the cat cerebellum.

The topographic organization of the climbing fiber (CF) responses was mapped in the rostral vermal cortex (lobules III, IV, and Va) of the cerebellum. Extracellular, single-unit recordings were obtained from 699 Purkinje cells in cats anesthetized with sodium pentobarbital. Approximately 72% of the CF responses were elicited by low-threshold or deep tactile stimulation, whereas the remaining units were unresponsive to any peripheral stimulation. On the basis of response characteristics, the vermal cortex was separated into an approximately 1-mm-wide medial zone and a 1 to 1.5-mm-wide lateral zone. The medial zone contained many unresponsive cells, except along the midline, where about 35% of the CF responses were elicited by deep stimulation at the base of the tail. The majority (78%) of the CF responses within the lateral vermal cortex represented various areas of the hindpaw, although representations of the forepaw (8%), tail (4%), and chin (0.6%), as well as unresponsive units (10%), were evident. The lateral vermal cortex contained a mediolateral topography of different receptive fields, although the topography was not sharply defined or equally displayed in all animals. The medial part of the lateral zone contained a representation of the ipsilateral forelimb in lobules IV and Va; the middle part had a representation of the medial or the lateral half of the hindpaw; and the lateral portion of the zone had an extensive representation of the distal hindpaw. The CF responses with similar receptive fields were often found in patches, which in some areas were arranged in layers from the inner to the outer areas of the sublobules. A particular body surface may be represented in multiple patches and in different lobules. Activation of the majority of CF responses within a sublobule may occur only during selected behaviors.