Encoding of locomotor signals by Purkinje cell complex spikes

Climbing fiber inputs to the cerebellar cortex drive low-frequency bursts of activity in Purkinje cells - known as complex spikes - which are thought to encode sensorimotor errors critical for movement refinement. Yet, the precise nature of these signals remains elusive for complex behaviors requiring the coordination of multiple body parts, such as locomotion. To understand the contribution of olivary inputs to the cerebellar cortex in locomotor coordination, we performed calcium imaging from Purkinje cell dendrites in unrestrained mice running on treadmills. Combining miniscope imaging with quantitative behavioral analysis allowed us to analyze population activity as animals adjust their interlimb and whole-body coordination over time. Preliminary analysis reveals widespread correlated activity along parasagittal axes within the intermediate cerebellum, indicative of spatially organized climbing fiber inputs to Purkinje cells and consistent with the existence of cerebellar microzones. Embedding population activity into a low-dimensional space, we identified functionally distinct ensembles of neurons encoding different stages of the gait cycle. Moreover, sudden changes in body kinematics appear to induce highly synchronous responses in Purkinje cell dendrites. Ongoing work aims to understand the evolution of this activity during locomotor learning and to causally test its contribution to locomotor coordination.