MODEL RELEASED. Parkinson's disease patient. Hand of an elderly man with Parkinson's disease is examined by a doctor. The doctor tests the wrist for cogwheel" tone, while the fingers are tested for slow movement (bradykinesia). Parkinson's disease is characterised by a shuffling unbalanced walk, rigid posture and slow trembling movements. Parkinson's disease is caused by degeneration of nerve cells in the basal ganglia of the brain. This causes a lack of dopamine, a brain chemical required for proper motor activity. The disease occurs mainly in the elderly, and is more common in men. Drug treatment minimizes the symptoms."