Rebuilding Cerebellar Network Computations from Cellular Neurophysiology

This schematic drawing shows the most relevant connections within a cerebellar module. The mossy fibers contact granule cells (GrC) and deep cerebellar nuclei (DCN) cells which, in turn, receive inhibition from the same common set of Purkinje cells (PC). Moreover, the interior olive (IO) cells emit climbing fibers that contact DCN cells and Purkinje cells (PC), which also project to the same DCN cells. An activate group of GrCs is in (red), while others (yellow) are laterally inhibited by the GoCs. The active GrCs excite the overlaying PCs (dark red) according to a vertical organization pattern (Bower and Woolston, 1983). The PCs inhibit DCN neurons which in turn inhibit the IO neurons. Note that, within a cerebellar module, different circuit elements communicate in closed loops. The mossy fibers contact granule cells and DCN cells which, in turn, receive inhibition from the same common set of Purkinje cells. Moreover, the IO cells emit climbing fibers that contact DCN and PC, which also project to the same DCN cells. The cerebellum has traditionally provided an ideal case for investigating the relationship between cellular neurophysiology and circuit functions, because of the limited number of neuronal types and the regular organization of its internal network (Figure 1). which proposed the first computational model of cerebellar function, was inspired by morphological determinations of the number of neurons and syn-apses but accounted for only very limited knowledge on functional properties of the cerebellar circuitry. In recent years, in association with remarkable developments of physiological technologies, important achievements at the cellular level have suggested that the original view needs to be revisited (Rokni et al., 2008). The papers in this special issue are focused on the relationship between cellular properties and circuit responses, which hold the key to control spike timing and long-term synaptic plasticity and eventually cerebellar functioning. In the cerebellum, inputs are conveyed through a double system formed by the mossy fibers and the climbing fibers. These inputs converge onto Purkinje cells, which eventually inhibit the DCN, representing the sole output of the circuit (Figure 1). Despite the wealth of available information, outstanding issues remain open about the spatial organization of granular layer activity, the discharge of Purkinje cells and deep cerebellar neurons, the mechanisms of circuit inhibition, the forms of long-term synaptic plasticity and their relationship with behavior. These aspects are covered by the papers in this special issue combining a careful literature review …