Tahon JN-00317-2010 revision 2 CSD and spike responses in cerebellar cortex 1 CURRENT SOURCE DENSITY CORRELATES OF CEREBELLAR GOLGI 1 AND PURKINJE CELL RESPONSES TO TACTILE INPUT

25 26 The overall circuitry of the cerebellar cortex has been known for over a century, but the 27 function of many synaptic connections remains poorly characterized in vivo. We used a 28 one-dimensional multi-electrode probe to estimate the current source density (CSD) of 29 Crus IIa in response to perioral tactile stimuli in anaesthetized rats, and to correlate 30 current sinks and sources to changes in the spike rate of co-recorded Golgi and Purkinje 31 cells. The punctate stimuli evoked two distinct early waves of excitation (at < 10 ms and 32 ~ 20 ms) associated with current sinks in the granular layer. The second wave was 33 putatively of cortico-pontine origin and its associated sink was located higher in the 34 granular layer than the first trigeminal sink. The distinctive patterns of granular-layer 35 sinks correlated with the spike responses of co-recorded Golgi cells. In general, Golgi cell 36 spike responses could be linearly reconstructed from the CSD profile. A dip in simple37 spike activity of co-registered Purkinje cells correlated with a current source deep in the 38 molecular layer, probably generated by basket cell synapses, interspersed between sparse 39 early sinks presumably generated by synapses from granule cells. The late (> 30 ms) 40 enhancement of simple-spike activity in Purkinje cells was characterized by the absence 41 of simultaneous sinks in the granular layer and by the suppression of co-recorded Golgi 42 cell activity, pointing at inhibition of Golgi cells by Purkinje axon collaterals as a likely 43 mechanism of late Purkinje cell excitation. 44