Depressive symptoms of Parkinson's disease (PD) patients are major predictors of their prognosis and quality of life. Using subthalamic nucleus (STN) deep brain stimulation (DBS) as an antidepressant could be a promising new direction. Existing methods of adjustment of DBS parameters aim at amelioration of the motor signs and therefore with inactivation of the STN motor territory only. Although the DBS parameter setting is believed to influence the mental state, there is no data that correlates stimulation parameters with mental state. The investigators hypothesize that the emotional territories of the STN have distinct electrophysiological properties and that specific stimulation of these emotional territories can influence the mental state and thus treatment with emotionally-adjusted DBS can improve the psychiatric symptoms of PD. In this project, the investigators intend to map the emotional territories of the STN using neuronal (single units) responses to emotional voices and to identify the emotional spectral signature of the STN single unit activity using spectral analysis and neuronal responses to emotional voices. The investigators also intend to investigate the emotional processing of PD patients by manipulating the stimulation of the subthalamic area. The proposed study will combine neural recording, stimulation and psychological tests to shed new light on emotional processing in the basal ganglia, as well as to provide better treatment for PD emotional disorders,

Inclusion Criteria:

1. Clinically definite PD treated / candidates for treatment with DBS (patients with advanced idiopathic PD who are deemed appropriate for DBS surgery).
2. Patients will be included in the study irrespective of whether a diagnosis of major depression (MDD) (mild to moderate but not severe MDD) is fulfilled at baseline. Patients without depression will be monitored in the study for evidence of treatment emergent depression. Patients with depression will be monitored for antidepressant effects of stimulation change.
3. Age 40-75 years
4. Male or female.
5. Competent and willing to give written informed consent

Exclusion Criteria:

1. Significant suicidal risk [Hamilton Depression scale item 3 (suicide) >2].
2. Comorbidity with any Psychotic Disorder, Bipolar Disorder, Post Traumatic Stress Disorder (PTSD), Eating Disorder.
3. Lifetime history of substance or alcohol dependence or of abuse in the preceding 12 months
4. Significant cognitive decline, as measured by Addenbrooke's Cognitive Examination (ACE) and the Frontal Assessment Battery (FAB).