The great gate: control of sensory information flow to the cerebellum.

An evident feature of the physiology of the inferior olivary nucleus is modulation of the responsiveness of neurons to peripheral stimulation by the behavioral state of the subject animal. The olivary response to self-generated sensory inputs, as well as to input predictable from association with other stimuli, is suppressed. This suppression occurs in part at the level of the inferior olivary nucleus itself. On the other hand, the cells respond readily to sensory inputs that are not anticipated. On a cellular level inferior olivary neurons exhibit two properties that might account for information gating. The first one is the organization of synaptic inputs on olivary spines in glomerular structures, where extrinsic inhibitory and excitatory inputs, confined to the same olivary dendritic spine, can efficiently cancel each other if they arrive within a certain time window. About half of the inhibitory inputs to olivary glomeruli originate in the deep cerebellar nuclei and are regarded as an inhibitory feedback. The second property is subthreshold membrane potential oscillations, a property of the electrotonically coupled olivary network. Extrinsic synaptic inputs to the nucleus modulate the subthreshold oscillations, and consequently, the response properties of olivary neurons. A considerable amount of indirect evidence indicates that the occurrence of oscillations corresponds to states of increased responsiveness of the neurons to peripheral stimulation. The sensory filtering role of the inferior olivary nucleus invites comparison between the cerebellum and cerebellar-like structures. This comparison sheds important light on the function of the cerebellum.