PARKINSON'S People with Parkinson's disease don't have enough dopamine – a chemical that allows messages to be sent to the parts of the brain that control movement and some forms of thinking. The disease targets and kills dopamine-producing nerve cells, or neurons, in part of the brain called the substantia nigra, although the disease does affect other nerve cells within the brain which may account for some of the other features of Parkinson’s such as problems with sleep, motivation, thinking, etc. Parkinson’s is also linked to the formation of clumps of a protein called alpha-synuclein in the brain. These abnormal protein clumps are called Lewy bodies.As dopamine nerve cells die, Parkinson’s patients develop tremors and rigidity, and their movements slow down. They might also lose their sense of smell or suffer from sleep disorders, depression, constipation and sometimes dementia in the later stages of the disease as the disease spreads out to involve other nerve cells.