clinically definite pd treated / candidates for treatment with dbs (patients with advanced idiopathic pd who are deemed appropriate for dbs surgery).

patients will be included in the study irrespective of whether a diagnosis of major depression (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.

age 40-75 years

male or female.

competent and willing to give written informed consent.

significant suicidal risk [hamilton depression scale item 3 (suicide) >2].

comorbidity with any psychotic disorder, bipolar disorder, post traumatic stress disorder (ptsd), eating disorder.

lifetime history of substance or alcohol dependence or of abuse in the preceding 12 months

significant cognitive decline, as measured by addenbrooke's cognitive examination (ace) and the frontal assessment battery (fab).