Parkinson's disease consists of a group of neurological disorders that can include symptoms of shaking, trembling, loss of muscle control, muscular rigidity, slow movement and long reaction times. It is a chronic, progressive and incurable disease of the central nervous system. It thus affects walking, talking, writing and swallowing.
The condition is linked to an imbalance between two brain chemicals, or neurotransmitters: dopamine and acetylcholine. The destruction of cells in a tiny region of the brain called the substantia nigra leads to a lack of dopamine, which is important in the control of movement.
In the USA there are approximately 500,000 suffering from the disease. In the UK in 1994 it was estimated that the disease cost more than £3 billion a year for the 112,000 sufferers (namely £30,000 per year each). 100 out of every 100,000 Australians have Parkinson's disease; among those over 70 years of age, 1000 of 100,000 are afflicted.
Damaged brain cells emit chemical noise, rather than a series of appropriate chemical signals. The brain has to sift through the unclear message to identify genuine movement signals, which slows reaction time from the normal 80 milliseconds (ms) to more than 250 ms, characteristic of Parkinson's patients, and also results in false movement commands. Slow reaction time is one basis for diagnosing the severity of Parkinson's disease.