Parkinson's disease is a disorder of certain nerve cells in the
brain that normally produce a chemical called dopamine, which
helps the brain direct and control movement. In Parkinson's
disease, these dopamine-producing nerve cells break down,
causing dopamine levels to drop and affecting the brain signals
that direct movement. The classic symptoms of Parkinson's
disease are shaking (tremor), stiff muscles (rigidity), and slow
movement (bradykinesia). A person with fully developed
Parkinson's disease may also have a stooped posture, a blank
stare or fixed facial expression, speech problems, and problems
with balance or walking. He or she may also have confusion and
memory loss. The cause of the disease is unknown. Parkinson's
disease usually begins in middle or late life, rarely before age
50—except in cases where genetic causes are suspected. The
disease usually progresses gradually over many years, often at
different rates in different people. There is no cure for
Parkinson's disease, but medicine and in so