Gating of neural error signals during motor learning
  Cerebellar climbing fiber activity encodes performance errors during many motor learning tasks, but the role of these error signals in learning has been controversial. We compared two motor learning paradigms that elicited equally robust putative error signals in the same climbing fibers: learned increases and decreases in the gain of the vestibulo-ocular reflex (VOR). During VOR-increase training, climbing fiber activity on one trial predicted changes in cerebellar output on the next trial, and optogenetic activation of climbing fibers to mimic their encoding of performance errors was sufficient to implant a motor memory. In contrast, during VOR-decrease training, there was no trial-by-trial correlation between climbing fiber activity and changes in cerebellar output, and climbing fiber activation did not induce VOR-decrease learning. Comparison of the two training paradigms suggests that the ability of climbing fibers to induce plasticity can be dynamically gated in vivo by the state of the cerebellar circuit, even under conditions where the climbing fibers are robustly activated by performance errors. 
Rhea R. Kimpo, Jacob M. Rinaldi, Christina K. Kim, Hannah L. Payne and   Jennifer L. Raymond
q-bio.NC