Parkinson’s disease is a neurodegenerative disease characterized by cell (neuronal) death of dopamine-producing cells. The area in the brain with the most substantial degeneration is called the substantia nigra, which is one of the main sources of dopamine for the brain. When Parkinson’s motor symptoms arise, at least 50% of the neurons in the substantia nigra have already died. Dopamine is a neurotransmitter that helps cells (neurons) communicate, and is especially important for movement. The death of cells producing dopamine causes a disruption in brain signaling to various parts of the body that control movement; thus, causing movement symptoms such as tremor, rigidity, or bradykinesia. The majority of medications developed for treating Parkinson’s disease act to directly or indirectly replace the brain dopamine deficiency.