The discharges of cerebellar Golgi cells during locomotion in the cat.

1. Extracellular recordings have been obtained from 134 units in the paravermal cortex of lobule V in the anterior lobe of the cerebellum in free-to-move cats. Each unit discharged action potentials in a characteristic pattern with no complex spikes. Previous investigators have described such discharges and have assigned them to Golgi cells. We provide further evidence to support this identification. 2. In cats which were sitting quietly, each putative Golgi cell discharged tonically at a low rate (overall mean (+/- S.D.) was 14.5 +/- 7.3 spikes/s). Eighty-one of the neurones were also recorded during steady walking on a moving belt and the discharge rate then averaged 17.7 (S.D. +/- 19.4) spikes/s. 3. All eighty-one putative Golgi cells discharged rhythmically during locomotion. Many different patterns of discharge were seen but as a population the neurons were most active in early stance and at the onset of the swing phase of the step cycle in the ipsilateral forelimb. 4. Over a range of different walking speeds (0.5-0.9 m/s) and of different uphill inclines (0-25 deg), putative Golgi cells discharged with similar patterns and rates, despite large changes in the vigour of the locomotor movements and in the amplitude of limb muscle electromyograms. 5. Groups of putative Golgi cells and of Purkinje cells recorded from restricted cortical regions produced discharges which fluctuated approximately in parallel during locomotion. However, a comparison of the activity patterns of pairs of closely adjacent Golgi and Purkinje cells revealed a wide variety of phase relations. The possible role of Golgi cells in determining the Purkinje cell output is discussed in the light of these findings.