ABSTRACT
In primates, parallel fibers average 6 mm in length and so affect a comparable length array of Purkinje cells that lie across the cerebellum. This is sufficiently long to span an entire deep cerebellar nucleus or to bridge adjacent nuclei. Despite functional subdivisions, the same circuit is repeated across the entire cerebellum, so it is likely that the same computations are performed by all parts of the cerebellum. During the execution of well rehearsed movements that are not too fast the cerebellum acts as a feedback device to compare motor intentions with motor performance, and works to reduce any mismatch between them. Sensory errors need to be converted into a pattern of nerve impulses that specify errors in motor performance, an operation of the inferior olivary nucleus. The predictions inherent to feedforward operation must be learnt during numerous trials attempting to perform the task.
