• Deep brain stimulation (DBS) involves the delivery of an electric current to a targeted area of the brain from a pulse generator, usually implanted in the chest wall, via fine cables tunnelled subcutaneously to electrodes placed in the brain.
• The pulse generator is similar to a cardiac pacemaker and can be programmed by an external device.
• It is possible to provide the individual with a degree of control of the stimulator.
• The pulse generator has a battery within it which will need to be replaced in a simple surgical procedure every few years.
• The structures in the brain that are targeted when treating Parkinson's disease are either of the following:
• The subthalamic nucleus (STN).
• The globus pallidus interna (GPi).
• The thalamus.
• The National Institute for Health and Clinical Excellence (NICE) has approved the use of STN-DBS and GPi-DBS procedures for people who meet all of the following criteria:
• They have motor complications that are refractory to best medical treatment.
• They are biologically fit with no clinically significant active comorbidity.
• They are levodopa responsive.
• They have no clinically significant active mental health problems, for example depression or dementia.
• NICE has approved thalamic DBS as an option for people with Parkinson's disease who predominantly have severe disabling tremor and where STN stimulation cannot be performed.
• STN-DBS is usually preferred; GPi-DBS and thalamic DBS are rarely performed in the UK.
• Limited evidence suggests that STN-DBS: reduces 'off' time, dyskinesia, and levodopa dose; improves motor impairments and disability; and improves quality of life at the expense of a small but significant risk of permanent neurological disability, and a possible increased risk of depression and suicide.

[National Collaborating Centre for Chronic Conditions, 2006; Pahwa et al, 2006]