Of Rats and Patients: Some Thoughts About Why Rats Turn in Circles and Parkinsons Disease Patients Cannot Move Normally

Animal behaviours that are easy to measure make great test systems for drug development, but we sometimes neglect to try to understand how their four-legged world view translates to our own. In this brief essay, I try to relate the turning behaviour that has been so useful in the development of drugs that act on Parkinsonian symptoms to the actual symptoms themselves. The thoughts led to a couple of predictions about Parkinsonian behaviour that help to link the bradykinesia that both patients and animals show. In conclusion, I suggest the general idea that dopamine acts to facilitate the learning and expression of the predicted outcomes of simple motor acts: perhaps as a different expression of the reward prediction for which dopamine is already thought to be important.