Cerebellar somatosensory mossy fibre input---Synaptic integration and synaptic plasticity

The present study has addressed two important issues for cerebellar function, the processing of mossy fibre (MF) information by granule cells and the role of synaptic plasticity in parallel fibre (PF) synapses. The experiments were performed on unanesthetized decerebrate cats. Whole cell recordings from granule cells (GCs) showed that mossy fibres converging on a GC were activated from the same modality/submodality and had similar peripheral receptive fields (RFs). These observations suggest that GCs are error-correcting elements that filter out uncorrelated activity (i.e. spontaneous MF activity). Climbing fibre (CF) evoked LTD of PF synapses on Purkinje cells (PCs) was long considered to be responsible for cerebellar learning. However, experiments with burst stimulation of PFs showed that PF input to PCs and interneurones was controlled by bidirectional reciprocal plasticity. Stimulation of PFs alone resulted in LTP of their synapses on Purkinje cells and LTD of synapses on interneurones whereas conjunctive stimulation of CFs and PFs had the opposite effect.