Mesoscale simulations predict the role of synergistic cerebellar plasticity during classical eyeblink conditioning

According to Marrs motor learning theory, plasticity at the parallel fibre to Purkinje cells synapse (pf-PC) is the main substrate responsible for learning sensorimotor contingencies under climbing fibre control. However, the discovery of multiple forms of plasticity distributed over different cerebellar circuit synapses prompts to remap the cerebellar learning sites. Here, we have simulated classical eyeblink conditioning (CEBC) using an advanced spiking cerebellar model embedding upbound and downbound modules that are subject to multiple plasticity rules. Simulations show that synaptic plasticity regulates the cascade of precise spiking patterns spreading throughout the cerebellar cortex and cerebellar nuclei. CEBC was supported by plasticity in both the pf-PC synapses and in the feedforward inhibitory loop passing through the molecular layer interneurons (MLIs), but only the combined switch-off of both sites of plasticity compromised learning significantly. By differentially engaging climbing fibre information and related forms of synaptic plasticity, both modules contributed to generate a well-timed conditioned response, but it was the downbound module that played the major role in in this process. The outcomes of our simulations closely align with the behavioural and electrophysiological phenotypes of mutant mice suffering from cell-specific mutations that affect processing of their PC or MLI synapses. Our data highlight that a synergy of bidirectional plasticity rules distributed across the cerebellum facilitate finetuning of adaptive associative behaviours at a high spatiotemporal resolution.