Page "Cerebellum" Paragraph 2

In addition to its direct role in motor control, the cerebellum also is necessary for several types of motor learning, the most notable one being learning to adjust to changes in sensorimotor relationships.

Several theoretical models have been developed to explain sensorimotor calibration in terms of synaptic plasticity within the cerebellum.

Most of them derive from early models formulated by David Marr and James Albus, which were motivated by the observation that each cerebellar Purkinje cell receives two dramatically different types of input: On one hand, thousands of inputs from parallel fibers, each individually very weak ; on the other hand, input from one single climbing fiber, which is, however, so strong that a single climbing fiber action potential will reliably cause a target Purkinje cell to fire a burst of action potentials.

The basic concept of the Marr-Albus theory is that the climbing fiber serves as a " teaching signal ", which induces a long-lasting change in the strength of synchronously activated parallel fiber inputs.

Observations of long-term depression in parallel fiber inputs have provided support for theories of this type, but their validity remains controversial.