Reward Prediction Error ([[RPE]]), is thought to be a the activator of learning when ther there is a difference between accepted reward and actual reward<ref>[http://www.pnas.org/content/early/2011/03/08/1014269108.full.pdf Glimcher, P. W. (2011). Understanding dopamine and reinforcement learning: the dopamine reward prediction error hypothesis. Proceedings of the National Academy of Sciences of the United States of America, 108 Suppl (Supplement_3), 15647–54]</ref>. but it is debated<ref>[http://www.ncbi.nlm.nih.gov/pubmed/17115078?dopt=Abstract article 2007]</ref>.