The purpose of this study is to identify factors predicting good results in patients treated with deep brain stimulation for Parkinson's disease. The study includes a comparison of two surgical methods used to provide this therapy.

The study will prospectively examine the effects of deep brain stimulation of the subthalamic nucleus (STN-DBS) on motor function, quality of life and cognitive function in Parkinson's disease (PD) patients treated at Rikshospitalet University Hospital. The aim is to identify which factors that predict good treatment outcome, in order to improve patient selection of this generally highly effective, but specialized and expensive treatment.

The study has several aims:

1. Randomized double-blind evaluation of the impact of using single vs. multiple electrode-recordings to guide electrode placement.
2. To identify factors predicting good effect on motor function and improvements of quality of life after deep brain stimulation of the subthalamic nucleus.
3. To identify cognitive and psychiatric changes related to deep brain stimulation of the subthalamic nucleus
4. To study social functioning of patients after STN-DBS and quality of life of patient caregivers

Inclusion Criteria:

• Diagnosis of Parkinson's disease
• Symptoms ≥ 5 years
• Severity of Parkinson's disease ≥ 20 points in UPDRS motor scale (scale 0-108) in OFF medication state
• Marked fluctuations of motor symptoms AND/OR troublesome dyskinesias AND/OR severe tremor AND/OR intolerable side-effects of dopaminergic drugs
• Failure of medical treatment to sufficiently control symptoms
• L-dopa responsive symptoms with ≥30% reduction in UPDRS motor score in drug ON state compared to OFF state OR severe l-dopa unresponsive tremor

Exclusion Criteria:

• Previous surgery for Parkinson's disease
• Marked axial motor symptoms unresponsive to treatment with l-dopa
• Dementia (Mattis dementia rating scale < 130).
• Patient suffering from untreated moderate or major depression or anxiety disorder
• Presence of other psychiatric disorder preventing necessary co-operation
• Brain MRI showing marked atrophy or white matter changes
• Increased risk of bleeding
• Presence of medical illness with short life expectancy
• Other surgical contra-indications