Figure 1:

Experimental design: A. Schematic shows the prevailing model of the proposed circuit for motor learning in which the cerebellum computes an estimate of the expected sensory consequence of the brain’s motor command (i.e., forward model). This estimate is then compared with the actual sensory feedback to compute the sensory prediction error. Single unit recordings were made in the rostral fastigial nucleus (rFN) which constitutes a major output target of the cerebellar cortex as well as vestibular nuclei (VN), which project to the spinal cord. B. Experimental set-up for learning paradigm in which resistive torque was applied to reduce head motion initially by one-half. C. Sequence of learning task. First, head movements and neuronal responses (not shown) were recorded before learning in both passive and active conditions. Second, the load was applied and held constant for the learning phase. Third, after the learning phase, the motor was randomly turned off for single ‘catch’ trials. Finally, the motor was completely turned off for the extinction phase.