Direction-Dependent Encoding of Forward and Inverse Models in the Same Purkinje Cells

Purkinje cells in the macaque oculomotor vermis encode direction-specific computations: CS-on opposed saccades show forward-model-like SS bursts, while CS-on aligned saccades show inverse-model-like CS timing.

• Why it matters: The cerebellum is thought to compute forward and inverse models, but it is unclear how both computations can coexist within the same Purkinje cell circuit.
• What they did: The authors recorded Purkinje cell activity during repetitive saccade paradigms that induce adaptation and fatigue, using each cell’s CS-on direction as a proxy for its cerebellar-nuclei projection side. They compared CS and SS timing and error sensitivity for CS-on opposed versus CS-on aligned saccades.
• The result: CS-on opposed saccades produced precisely timed, sharp SS bursts at onset scaling with peak velocity and highest CS error sensitivity after saccades, consistent with a forward model updated from post-movement error; CS-on aligned saccades showed broader SS modulation near offset, CS error sensitivity highest before saccades, and CSs linked to target location and initial eye position with reduced saccade amplitude, consistent with an inverse model.

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