By Helen Briggs
Health reporter, BBC News
The surgery blocks electrical signals from specific parts of the brain
Brain surgery to treat Parkinson's disease is more effective than medication alone, a study has found.
More than 300 patients in the UK were fitted with electrodes that deliver an electric current deep within the brain.
The technique, known as deep brain stimulation, activates areas of the brain that control movement, improving symptoms such as tremors and stiffness.
One person in every 500 has Parkinson's but surgery is generally used only as a last resort.
Deep brain stimulation involves implanting a wire, with electrodes at its tip, into one of three areas of the brain.
The wire is connected to a small "neurostimulator" unit rather like a pacemaker, which is implanted under the skin of the chest.
This unit sends electrical impulses along the wire and into the brain.
The impulses block the electrical signals that cause Parkinson's disease symptoms.
The UK team investigated 366 patients, who received either surgery and medication, or medication alone.
When followed up after a year, the researchers, based in Birmingham, Bristol, Liverpool, Oxford and London, found those who had undergone surgery reported a better quality of life.
Writing in Lancet Neurology, they say surgery is an important treatment option for patients with Parkinson's.
Professor Keith Wheatley of the University of Birmingham told the BBC: "It is not a cure. What it does is help control symptoms more than medication alone."
The 10-year study, funded by the charity Parkinson's UK, the Medical Research Council and the Department of Health, is said to be the largest trial of its kind in the world.
Dr Kieran Breen, director of research and development at Parkinson's UK said access to deep brain stimulation was "patchy".
He said the surgery should be made available to people who need it, when they need it.
Affects about 120,000 people in the UK
Most people who get Parkinson's are aged 50 or over
A loss of nerve cells in the brain causes the symptoms of Parkinson's to appear
"There's still a postcode lottery in the UK when it comes to accessing Parkinson's services," he added.
"We want to make sure that everyone with Parkinson's has equal access to the care and support they need, wherever they live."
Bob Garland, aged 65, from Plymouth, was diagnosed with Parkinson's 18 years ago. He had the surgery at Frenchay Hospital in Bristol in 2002.
He said: "It has taken away the extremes of my movement problems."
He encouraged others to seek an opinion on whether the operation was suitable for them.
"You have to go into it with a very positive attitude," he added.