The cerebellar network: From structure to function and dynamics (original) (raw)

Since the discoveries of Camillo Golgi and Ramón y Cajal, the precise cellular organization of the cerebellum has inspired major computational theories, which have then influenced the scientific thought not only on the cerebellar function but on the brain as a whole. However, 6 major issues revealing a discrepancy between morphologically inspired hypothesis and function have emerged. (1) The cerebellar granular layer does not simply operate a simple combinatorial decorrelation of the inputs, but performs more complex non-linear spatio-temporal transformations and is endowed with synaptic plasticity. (2) Transmission along the ascending axon and parallel fibers does not lead to beam formation but rather to vertical columns of activation. The olivo-cerebellar loop could perform complex timing operations rather than error detection and teaching. (4) Purkinje cell firing dynamics are much more complex than for a linear integrator and include pacemaking, burst-pause discharges and bistable states in response to mossy and climbing fiber synaptic inputs. (5) Long-term synaptic plasticity is far more complex than traditional parallel fiber LTD and involves also other cerebellar synapses. (6) Oscillation and resonance could set-up coherent cycles of activity designing a functional geometry that go far beyond pre-wired anatomical circuits. These observations clearly show that structure is not sufficient to explain function and that a precise knowledge on dynamics is critical to understand how the cerebellar circuits operate. The intuitions of Golgi and Cajal concerned the functional organization of single neurons and of the networks they are part of, and led to hypothesize the existence of the synapses and to fund the neuron doctrine more than to reveal the intimate cerebellar mechanisms. Nonetheless, by clearly identifying the main cellular types and their fundamental connections, the discoveries of these two scientists have provided the basic step for subsequent cerebellar research.