Spontaneous activity of cerebellar Purkinje cells and their responses to impulses in climbing fibres.

1. Spontaneous discharges and evoked responses of Purkinje cells have been studied in the anterior lobe vermis of the cerebellum in cats anaesthetized with thiopentone sodium.2. Spontaneous activity was of two kinds: (a) single spikes which occurred in long trains and were discharged at average frequencies of 50-125/sec and (b) burst responses due to climbing fibre (CF) activation of the cell. These occurred at an average frequency close to 1/sec.3. CF responses were evoked by either stimulation of the Abeta fibres of the superficial radial nerve (SRN) or by an electrode inserted into the deep white matter near the fastigial nucleus (JF electrode).4. A suppression of the discharge of single spikes was frequently observed to follow a CF response, whether it occurred naturally or was produced by a stimulus. These pauses in spontaneous discharge (post-CF pause) lasted for approximately 100 msec, but they did not have a one-to-one relationship with the CF responses. Occasionally a pause in the spontaneous activity was elicited by stimuli that failed to evoke the cell.5. For a period following a peripheral stimulus, a Purkinje cell could not be further excited by a second peripheral stimulus (interaction). JF stimulation could still excite the cell. Evidence was obtained that there was no significant inhibition during the period of depressed excitability to peripheral stimulation.6. The control over the input of activity to the cerebellum through the CF system appears to be imposed at an extra-cerebellar site. The olivary nuscles was suggested as a strong possibility.7. Some possible mechanisms responsible for the post-CF pause were discussed. Disfacilitation of Purkinje cells by suppression of granule cell discharges seems to give the best fit to the data.