Climbing fibre inputs to cerebellar Purkinje cells from trigeminal cutaneous afferents and the SI face area of the cerebral cortex in the cat.

1. An investigation was made of climbing fibre (CF) activity evoked in single Purkinje cells in the cerebellum by electrical stimulation of trigeminal cutaneous afferents, the face area of the SI cortex, and the superficial radial nerve, in Nembutal-anaesthetized cats. In addition, both the extent of the cutaneous receptive fields of individual Purkinje cells on the face and the CF responses evoked in these cells by controlled natural stimulation were examined. 2. The pattern of convergence from these inputs on to individual Purkinje cells was found to be complex. DF responses were evoked in 67% of trigeminally-activated cells by electrical stimulation of more than one trigeminal branch. An excitatory CF convergence from the face area of the SI cortex was found on 68% of trigeminally activated cells; 23% also responded to stimulation of the superficial radial nerve. 3. In 81% of the Purkinje cells which were activated by trigeminal nerve stimulation, CF responses were readily elicited by gentle mechanical stimulation of the facial skin. A qualitative relationship was established between the size of the peripheral field of a Purkinje cell, and the probability of convergence on to that cell from the SI cortex. 4. Recordings were made from a limited number of Purkinje cells which were responsive to electrical stimulation of bilateral trigeminal branches and the superficial radial nerve. However, CF responses in these cells often could be elicited only by high intensity stimulation. It is suggested that these cells are analogous to, or perhaps an extension of the population of Purkinje cells described in the anterior lobe which are excited via the ventral funiculus pathway in the spinal cord only by stimulation of 'flexor reflex afferents' in bilateral limb nerves.