I N Contrast, M a R R Fig. 1 ) . The

The M a r r and Albus t h e o r i e s o f t h e cerebel lum are compared and contrasted. They are shown t o be s i m i l a r i n t h e i r ana l ys i s of t h e function o f t h e mossy f ibers , granule c e l l s , Golg i c e l l s , and Purkinje c e l l s . They both pred ic t motor learning i n the p a r a l l e l f i b e r synapses on the Purkinje dendrites mediated by concurrent climbing f i b e r input. T h l s p red i c t i on has been confirmed by exper imenta l evidence. I n contrast, M a r r p red ic ts these synapses would be f a c i l i t a t e d by learning, w h i l e Albus p r e d i c t s they would be weakened. Exper imenta l evidence conf i rms synapt ic weakening.