Origin and sagittal termination areas of cerebro-cerebellar climbing fibre paths in the cat.

Climbing fibre responses were recorded in the cerebellar anterior lobe on stimulation of the cerebral cortex. A zonal pattern was demonstrated in the cortical projection, which was related to the cerebellar sagittal zones, as identified from peripheral climbing fibre input. In all zones, except c2, a co-variation of the responses evoked on peripheral nerve stimulation and on stimulation of the corresponding part of the sensorimotor cortex was found. There was a bilateral projection to the a, b, c2 and d1 zones which also, to a varying extent, receive a bilateral peripheral input. The x, c1 and c3 zones, receiving an ipsilateral peripheral input, were activated exclusively from the contralateral cortex. Stimulation of the posterior sigmoid gyrus (p.s.g.) evoked responses in all the zones. These responses had, in all zones except d1, lower thresholds and shorter latencies than the responses from other cortical areas. Two separate p.s.g. areas were shown to project to the pars intermedia zones (c1, c2, c3 and d1), the lateral area to the caudal parts and the medial area to the rostral parts of the zones. In contrast, the b zone received a projection from only one p.s.g. area, centred between, but overlapping, the two areas projecting to the pars intermedia zones. Stimulation of the anterior sigmoid gyrus evoked short-latency responses in the d1 zone and long-latency responses in all other zones. Stimulation of the first and second somatosensory areas (SI and SII) was generally less effective in evoking climbing fibre responses than was stimulation of the p.s.g. The only exception was the c2 zone, in which responses were evoked from the SII with nearly as low thresholds and short latencies as on p.s.g. stimulation. From the parietal cortex, long-latency responses were regularly evoked in the d1 zone and less frequently in the a, b and c2 zones.