"Patients having deep brain stimulation (DBS) are fitted with a neurostimulator, a device similar to a heart pacemaker, which is connected to electrodes placed in certain parts of the brain.
The electrical implant is connected to a small battery under the skin in the person's chest or abdomen to generate small electrical signals to stimulate the brain.
This is controlled by a hand-held device which can be switched on and off.
When switched on, the patient benefits from the blocking of abnormal nerve signals which trigger the disabling symptoms.
The operation costs around £30,000 and is currently only considered on the NHS for patients with very advanced disease.
The latest trial using a DBS system made by US firm Medtronic is the first to look at patients with early symptoms.
After two years, those having surgery and drugs had a 26 per cent improvement in quality of life compared with drugs alone and a range of other advances."