Semi Sermet, PhD

In the cerebellar cortex, the granule cell (GC) layer is thought to facilitate the discrimination of activity patterns arising from mossy fibers (MFs) in order to learn context-dependent, temporally precise actions. Dynamical mechanisms such as short-term synaptic plasticity between MF inputs to GCs are thought to enhance decorrelations between input activity patterns and generate diverse activity basis sets within the population of GCs for temporal learning. Using genetically encoded fast-calcium indicator GCaMP8f, we demonstrate that coherent MF activity is transformed into diverse, brief GC activity transients in both brain slices and awake mice. Using in situ synaptic recordings, we provide evidence that the diverse synaptic strength and short-term plasticity of MF-GC synapses could mediate this transformation. Furthermore, GC temporal dynamics across cerebellar lobules mimicked differences in their synaptic dynamics. Together these results support the conclusion that the heterogeneity of short-term plasticity of MF-GC synapses sharpens GC responses and increases temporal sparsity in a region-specific manner. This synaptic transformation is likely to facilitate the temporal associations needed to acquire the precise output dynamics required to fine-tune motor and cognitive actions