Parkinson's is caused by damage in the part of the brain which is responsible for making dopamine. You may be wondering ... dopa what? Dopamine is a signaling chemical (neurotransmitter) in the brain. Dopamine plays a role in:
Coordinating your movements
Memory and learning
Experiencing pleasure and pain
Keeping you awake and alert during the day
(All really important things...right?)
Dopamine is made in a specific part of the basal ganglia called the substantia nigra. As Parkinson's progresses, the cells in the substantia nigra are damaged and less able to make dopamine. Typically by the time motor symptoms start, your dopamine production is down by 60-80%. There is an imaging technique called a DAT scan which looks at the dopamine levels in this part of the brain. This can not tell if you have PD, it can only tell that you have low levels of dopamine.
This is why medications like carbidopa-levadopa and dopamine agonists (chemicals that are like dopamine) can help with the symptoms of PD. The main difference between levodopa and dopamine agonists is that levodopa is converted in the brain to dopamine and dopamine agonists act like dopamine without having to be converted to dopamine.
Decreased dopamine in your brain can actually make it harder to stay engaged, focused and motivated to do everyday tasks. Besides medication, there are other things you can do to help with this. In research with mice, it has been found that exercise can help the brain use dopamine more effectively. Exercise has also been found to increase a chemical called GDNF (glial-derived neurotrophic factor), which can help decrease how vulnerable dopamine neurons are to damage.