Encoding of error and learning to correct that error by the Purkinje cells of the cerebellum

The primary output cells of the cerebellar cortex, Purkinje cells (P-cells), make kinematic predictions about ongoing movements via high-frequency simple spikes (SS), but receive sensory error information about that movement via low-frequency complex spikes (CS). How is the vector space of sensory errors encoded by this low-frequency signal? Here, we measured P-cell activity in the oculomotor vermis during saccades, then followed the chain of events from experience of visual error, generation of CS, modulation of SS, and ultimately change in motor-output. We found that while error direction affected probability of CS, error magnitude altered its temporal distribution. Production of CS changed the SS on the next trial, but regardless of the actual visual error, this change biased the movement only along a vector that was parallel to the P-cell’s preferred error. From these results, we inferred the anatomy of a sensory-to-motor adaptive controller that transformed visual error vectors into motor-corrections.