Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Parkinson's Disease ?
    ### Response:
    Dopamine is a brain chemical messenger, or neurotransmitter. It is responsible for transmitting signals between a brain region called the substantia nigra and multiple brain regions. The connection between the substantia nigra and the corpus striatum is critical to produce smooth, purposeful movement.
    