The main area involved in motor learning is the cerebellum. Some models of cerebellar-dependent motor learning, in particular the Marr-Albus model, propose a single plasticity mechanism involving the cerebellar long-term depression (LTD) of the parallel fiber synapses onto Purkinje cells. These modifications in synapse activity would mediate motor input with motor outputs critical to inducing motor learning. However, conflicting evidence suggests that a single plasticity mechanism is not sufficient and a multiple plasticity mechanism is needed to account for the storage of motor memories over time. Regardless of the mechanism, studies of cerebellar-dependent motor tasks show that cerebral cortical plasticity is crucial for motor learning, even if not necessarily for storage.