Is Purkinje Neuron Hyperpolarisation Important for Cerebellar Synaptic Plasticity? A Retrospective and Prospective Analysis.

Two recent studies have demonstrated that the dendritic Ca signal associated with a climbing fibre (CF) input to the cerebellar Purkinje neuron (PN) depends on the membrane potential (V). Specifically, when the cell is hyperpolarised, this signal is mediated by T-type voltage-gated Ca channels; in contrast, when the cell is firing, the CF-PN signal is mediated by P/Q-type voltage-gated Ca channels. When the CF input is paired with parallel fibre (PF) activity, the signal is locally amplified at the sites of PF-activated synapses according to the V at the time of the CF input, suggesting that the standing V is a critical parameter for the induction of PF synaptic plasticity. In this review, I analyse how the V can potentially play a role in cerebellar learning focussing, in particular, on the hyperpolarised state that appears to occur episodically, since PNs are mostly firing under physiological conditions. By revisiting the recent literature reporting in vivo recordings and synaptic plasticity studies, I speculate on how a putative role of the PN V can provide an interpretation for the results of these studies.