Mossy and climbing fibre mediated responses evoked in the cerebellar cortex of the cat by trigeminal afferent stimulation.

1. The trigeminal input to the cerebellar cortex was studied by recording mass and unitary resonses evoked by electrical stimulation of individual trigeminal cutaneous and muscle nerve branches, in cats lightly anaesthetized with sodium thiopentone. 2. The trigeminal projection area of the cerebellar cortex comprised essentially lobule HVI, but included adjacent folia of lobules HV and HVIIA. 3. Each trigeminal branch had a 'patchy' representation throughout the projection area and there was extensive convergence of individual afferents at each site. Exact combinations of convergent inputs varied between loci, the projection from the muscle nerve being weaker. No other differential representation of individual trigeminal branches was evident. 4. Responses were evoked by stimulation of both ipsi- and contralateral trigeminal afferents but contralateral projections were present at fewer sites. 5. Mass responses to stimulation of individual trigeminal branches comprised mossy fibre and climbing fibre-mediated potentials, although both components were not always present. Latencies for mossy and climbing fibre responses, evoked by ipsilateral nerve stimulation, were in the ranges 5--8 msec and 11--29 msec respectively. 6. Unitary responses of Purkinje cells activiated by trigeminal inputs also revealed convergence from individual ipsilateral afferent sources (28% influenced by one ipsilateral trigeminal branch, 48% by two branches, 17% by three branches and 7% by four branches). 7. Response patterns comprised one or more of the following: short latency (3--8 msec) simple, mossy fibre-mediated spikes, 'delayed' (10--25 msec) simple spikes and climbing fibre-mediated multiple spike bursts (9--35 msec).