Conceptual illustration comparing a clinical checklist to diagnosis Parkinson's disease to the brain. Parkinson's disease causes movement disorders from the decreased stimulation of the motor cortex. The main clinical symptoms include tremor, rigidity, akinesia/bradykinesia and postural instability. The parts of the brain affected (highlighted in the illustrations) are the globus pallidus, the putamen, substantia nigra, the subthalamic nucleus and the thalamus.