The morphogenesis of motor rituals in rats treated chronically with the dopamine agonist quinpirole.

Rats injected repeatedly with the dopamine agonist quinpirole develop motor rituals that evolve through a cascade of 4 behavioral processes. The 1st involves increased activity. The 2nd involves increased path stereotypy, reflected in traveling repeatedly along the same few paths. The 3rd is an increase in the frequency of stopping in a few places, along with a decrease in stopping in other places. The 4th is a decrease in the repetition of movements performed in the specific stopping places. Altogether, these processes culminate in stereotypy, a typical short set of movements composed of a single performance of each movement type. Thus, stereotypy arises from changes in the temporal and spatial organization, but not the content, of behavioral patterns. These results provide a model for the development of motor rituals and their linkage to normal behavior and to the physical properties of the environment.