The marr–Albers–ito model

Motor learning in  the  cerebellum  involves alterations  in  the  strengths of  synapses between parallel fibers  (pf ) and  PC (Purkinje cells). Those  synapses that are  active  at exactly  the  same time  that there is climbing fiber  input to the  PC experience a reduction in the  synaptic strength a kind  of spike  timing dependent plasticity called LTD (long-term depression).

In the Marr–Albers–Ito model of motor learning the frontal cortex through the corticopontine cerebellar tract gives the mossy fiber–parallel fiber inputs and the climbing fibers from the inferior olive are thought to transmit error signals. All the pf–PC synapses which happen to be activated through a pattern of mossy fiber inputs at the similar time as climbing fiber error signals arrive will show Long Term Depression. Synapses not concurrently active are unchanged. Consequently, parallel fiber activity at the depressed synapses excites Purkinje cells less, thus reducing their inhibitory output on deep cerebellar nuclei. The whole effect is that synapses at which LTD occurs enhance cerebellar output.