Voltage- and Branch-specific Climbing Fiber Responses in Purkinje Cells

Climbing fibers (CFs) provide instructive signals driving cerebellar learning. However, conflicting experimental studies have been reported about the reliability of CF mediated Ca2+ influx in Purkinje cell (PC) distal dendrites. Mechanisms causing the wide variation in duration and spikelet numbers of complex spikes (CSs) have not been explored systematically. Using a new experimentally validated PC model, we describe the full range of modifiability of CF responses to explain the experimental data and make new predictions. We find voltage state gates the initiation and propagation of dendritic spikes. PC dendrites exhibit inhomogeneous excitability with individual branches as computational units for CF input. Somatic CSs are regulated by voltage state, CF activation phase and instantaneous CF firing rate. Concurrent synaptic inputs can affect CSs by modulating dendritic responses in a spatially precise way. These voltage- and branch-specific CF responses will increase dendritic computational capacity and give PCs an active role in integrating CF signals.