Parkinson's disease is a progressive disorder of the nervous system which causes tremors, delayed movements and rigidity. It affects 120,000 people in the UK.
It is not fatal but reaction to treatment varies. There is no cure but the drug levodopa can relieve the symptoms – though it stops being effective after three to five years and extra drugs are frequently needed.
The disease is caused by a loss of nerve cells in one area of the brain, leading to a reduction in dopamine, a chemical that regulates movement.
The cause is unknown but is thought to be partly genetic and partly environmental. It is more common in men and tends to start around the age of 60. In long-term cases, the brain can sometimes be stimulated using electrodes implanted in the brain.
Tiny electric impulses are passed through the electrodes to stimulate the part of the brain affected by the disease. The technique has been shown to ease the symptoms in some patients.