Correlations between Purkinje Cell Single Unit Activity and Simultaneously Recorded Field Potentials in the Immediately Underlying Granule Cell Layer Running Head: Correlations between Purkinje and Granule Cells

Evidence from both anatomical and physiological studies suggests that the ascending segment of the granule cell axon provides a large, driving input to overlying Purkinje cells. In the current experiments we used dual recording electrodes to simultaneously record spike activity of Purkinje cells and multiunit field potential activity in the directly underlying granule cell layer. These dual recordings were performed both during periods of spontaneous (“background”) firing, and also following peripheral tactile stimulation. The results demonstrate that, in the large majority of cases, there is a strong positive correlation between spontaneous Purkinje cell simple spikes and spontaneous activity in the immediately underlying granule cell layer. The strength of this correlation was dependent on both the firing rate of the Purkinje cell as well as on the rate of granule cell layer multiunit activity. In addition, for any given pair of recordings, the correlation seen during spontaneous activity accurately predicted the magnitude and time course of responses evoked by peripheral tactile stimulation. These results provide additional evidence that the synapses associated with the ascending segment of the granule cell axon have a substantial influence on Purkinje cell output. This relationship is considered in the context of our ongoing reevaluation of the physiological relationship between cerebellar granule and Purkinje cells.