Corollary Discharge Signals in the Cerebellum

Abstract

The cerebellum is known to make movements fast, smooth, and accurate. Many hypotheses emphasize the role of the cerebellum in computing learned predictions important for sensorimotor calibration and feedforward control of movements. Hypotheses of the computations performed by the cerebellum in service of motor control borrow heavily from control systems theory, with models that frequently invoke copies of motor commands, called corollary discharge. This review describes evidence for corollary discharge inputs to the cerebellum and highlights the hypothesized roles for this information in cerebellar motor-related computations. Insights into the role of corollary discharge in motor control, described here, are intended to inform the exciting but still untested roles of corollary discharge in cognition, perception, and thought control relevant in psychiatric disorders.

Keywords: Cerebellar; Corollary discharge; Efference copy; Mossy fibers; Motor control; Reafference.

Figure 1.

How CD signals to the cerebellum relate to motor control deficit hypotheses. A) A schematic representation of dysmetric reaching movement trajectories, characterized by oscillatory movements around target (dot), which emerges with cerebellar damage. B) Comparison of slow feedback-error control systems, which resemble dysmetric movements, with feedforward control. Feedforward control uses predictive output to drive movement, avoiding oscillation. C) Hypothesized framework for cerebellar use of CD in predictive forward model computations. Panel C aligns “Computations” in the first column with “Structures and Circuitry”, representing regions of the cerebellum that produce these signals. Starting at the bottom left, following arrows: CD and sensory information enter the cerebellum via mossy fibers. Information is re-expressed in granule cells and scaled at Purkinje neurons through associative plasticity mechanisms under the control of climbing fibers. Together this plasticity is hypothesized to produce Purkinje patterning that matches sensory or kinematic predictions. Purkinje neurons project to the output structures of the cerebellum, the cerebellar nuclei, which send axons out of the cerebellum to influence downstream targets. One implementation of feedforward control uses these codes, called forward models, in conjunction with sensory feedback to identify mismatches of expected from actual outcomes to perform corrections, interpret sensory information and learn.