Vagal and somatic representation by the climbing fiber system in lobule V of the cat cerebellum.

The organization of the climbing fiber representation of the vagal afferents and the body surface in the vermal and intermediate zones of lobule V was examined in cats anesthetized with alpha-chloralose. Extracellular single-unit recordings were made from 428 Purkinje cells. Electrical stimulation of the vagus nerve elicited climbing fiber responses in 40% of the cells, most of which had convergent somatic input. Activation of A delta vagal afferent fibers accounted for 65% of the responses, whereas the A beta fibers involved 27% and the C fibers included 8% of the responses. The responses driven by vagal nerve stimulation were encountered throughout the lobule, although a significantly increased representation of the vagus was identified for 3 longitudinal 0.5 mm wide sectors (two in the vermis and one in the intermediate region). In the vermis, the fine-grain organization consisted of a mixture of representations of the various parts of the body surface with and without convergent vagal input, although there was little convergence in the medial vermis where many of the responses were elicited by only vagal nerve stimulation. In the intermediate cortex, most of the vagal climbing fiber representation was convergent with forelimb input. These results suggest that vagal input into the cerebellum could have important modulatory effects on the cerebellar somatosensory input.