Figure 9

Forward model-based control scheme (top panel) and inverse model-based control scheme (middle panel). Forward model: the message dedicated to the peripheral motor apparatus A is sent with an efference copy transmitted to the cerebellum A'. Instructions originating from higher motor centers (such as the premotor cortex) reach a comparator (grey circle). The comparator drives the motor cortex (a), which in turns drives lower motor centers in the brainstem and spinal cord. Efference copies are used to perform future predictions. Cerebellar microcircuits are necessary to learn how to make appropriately these predictive codes. Inverse model: A corresponds to the motor apparatus/control object. Cerebellar cortex working in parallel with the motor cortex and forming an internal model with a transfer function a' reciprocally equal to the dynamics of the control object (a' = 1/A). The input to the cerebellum is the desired trajectory, the output is the motor command. The bottom panel illustrates the model of the wave-variable processor for the intermediate cerebellum and the spinal cord gray matter. These structures contribute to motion control by processing control signals as wave variables. These wave variables are combinations of forward and return signals ensuring stable exchanges despite destabilizing signal transmission delays (adapted from [76].