THE DETECTION AND GENERATION OF SEQUENCES AS A KEY TO CEREBELLAR FUNCTION - EXPERIMENTS AND THEORY

Starting from macroscopic and microscopic facts of cerebellar histolog y, we propose a new functional interpretation that may elucidate the r ole of the cerebellum in movement control. The idea is that the cerebe llum is a large collection of individual lines (Eccles's ''beams'': Ec cles et al. 1967a) that respond specifically to certain sequences of e vents in the input and in turn produce sequences of signals in the out put. We believe that the sequence-in/sequence-out mode of operation is as typical for the cerebellar cortex as the transformation of sets in to sets of active neurons is typical for the cerebral cortex, and that both the histological differences between the two and their reciproca l functional interactions become understandable in the light of this d ichotomy. The response of Purkinje cells to sequences of stimuli in th e mossy fiber system was shown experimentally by Heck on surviving ''m ovement'' of the stimuli along the folium, produces a powerful volley in the parallel fibers that strongly excites Purkinje cells, as eviden ced by intracellular recording. The volley, or ''tidal wave,'' has max imal amplitude when the stimulus moves toward the succession of stimul i has no effect when they ''move'' in the opposite direction. Synchron ous activation of the stimulus electrodes also had hardly any effect. We believe that the sequences of mossy fiber activation that normally produce this effect in the intact cerebellum are a combination of moto r planning relayed to the cerebellum by the cerebral cortex, and infor mation about ongoing movement, reaching the cerebellum from the spinal cord. The output elicited by the specific sequence to which a ''beam' ' is tuned may well be a succession of well timed inhibitory volleys ' 'sculpting'' the motor sequences so as to adapt them to the complicate d requirements of the physics of a multijointed system.