Figure 1.
Schematics of motor control and the cerebellar circuit. (A) An internal forward model receives time-delayed sensory feedback (x(t − t delay) and efference copy (u (t)) and predicts a current state ( (t)) (bottom row). Difference between movement goal (xgoal) and predicted state ( (t)) drives a feedback controller to generate a control signal (u (t)), which in turn steers the controlled plant (top row). (B) Schematics of the neural circuit in the cerebellum from mossy fibers (MFs) to dentate nucleus cells (DNCs). Note that this feedforward circuitry resembles that of an internal forward model, indicating that the cerebellar input representing a time-delayed state is converted into the cerebellar output representing a current state. The numbers accompanied by the cell labels denote the relative numbers of cells in comparison with Purkinje cells (PCs), illustrating the expansion from MFs to granule cells (GCs) and the compression from MFs to DNCs. These numbers were calculated from corresponding numbers listed in Ito (1984).