Parkinson's disease occurs when certain nerve cells (called neurons) in an area of the brain known as the substantia nigra die or become impaired. Normally, these neurons produce an important brain chemical known as dopamine. Dopamine is a chemical messenger responsible for transmitting signals between the substantia nigra and the next "relay station" of the brain, the corpus striatum, to produce smooth, purposeful muscle movement.
A loss of dopamine causes the nerve cells of the corpus striatum to fire out of control, leaving people unable to direct or control their movements in a normal manner. Parkinson's research studies have shown that people with the condition have lost 80 percent or more of the dopamine-producing cells in the substantia nigra.
But why this nerve death or impairment happens is still unknown, although significant findings by research scientists continue to yield fascinating new clues and several theories about Parkinson's disease and its causes.
Current theories regarding the cause or causes of Parkinson's disease include: