p550fig15.20 Adaptively timed conditioning of Long Term Depression, or LTD, occurs in the cerebellum at synapses between parallel fibres and Purkinje cells, thereby reducing inhibition of subcortical nucleus cells and enabling them to express their learned movement gains within the learned time interval.  Also see Figure 15.21.<BR>||  [CS-Activated input pathways parallel fibres, US-Activated climbing fibres]-> [Subcortical nucleus (gain control), Cerebella cortex- Purkinje cells (timing)].