Cortical and peripheral modification of cerebellar climbing fibre activity arising from cutaneous mechanoreceptors.

1. In cats anaesthetized with Nembutal climbing fibre (CF) responses evoked in individual cerebellar Purkyne cells by mechanical stimulation of the skin were conditioned by preceding stimuli both to the periphery and to the precruciate area of the cerebral cortex.2. Cortical stimulation, generally subthreshold for evoking a CF response itself, induced an inhibition of cutaneous evoked CF responses in 65% of all Purkyne cells tested. The maximum inhibition ranged from 40 to 100% of the control responses at conditioning-testing intervals of 30-70 msec and the duration of the inhibition was usually 125 msec.3. In most cases the corticofugal inhibition of cutaneously evoked CF responses was mediated by inhibitory mechanisms outside the cerebellar cortex, probably at relays within the spino-olivocerebellar pathways. Purkyne cells undergoing corticofugal inhibition were distributed widely within both the vermis and the pars intermedia of the anterior lobe.4. In 40% of all Purkyne cells tested, there was evidence for afferent inhibition of their peripherally evoked CF responses as revealed by conditioning stimuli applied to the skin outside the receptive field. Again it was found that the inhibition was exerted at levels prior to the cerebellum.5. It is concluded that the afferent input transmitted to Purkyne cells via climbing fibres can be modified by corticofugal and peripheral influences exerted on the relays of the CF pathways outside the cerebellar cortex.