DRD2 and Parkinson disease: The other four versions of the model are used to simulate PD patients affected by four different impairments of the dopaminergic system: (a) a reduced synchronization between the dopaminergic phasic burst and the movement onset; (b) a reduced peak of the dopaminergic phasic peak; (c) a reduced tonic dopamine baseline level; (d) a reduced responsiveness of dopamine D2 receptors.