[Pathophysiology of abnormal movements in Parkinson's disease]

Major parkinsonian motor symptoms, i.e., bradykinesia, muscular rigidity, and resting tremor, are due to abnormalities in the motor circuit of the basal ganglia caused by loss of nigrostriatal dopamine neurons. Bradykinesia results from increased activity with altered firing patterns of the output nuclei of the basal ganglia. Exaggerated long-latency reflex or decreased Ib inhibition of the spinal reflex network have been suggested to underlie rigidity, but the relationship between these reflex abnormalities and the altered activities of the basal ganglia in the parkinsonian state remains unclear. The central oscillator for parkinsonian tremor has been localized in the basal ganglia circuit, and the cerebellar system also participates in generation of the tremor. Dyskinesia and dystonia may develop from decreased activity with altered firing patterns of the output nuclei of the basal ganglia.