The total length of the study is 15 months. First, the patients will be screened as to your suitability for this study. This will happen while the patients are performing the standard pre-operative assessments (including a videotaped L-dopa challenge, a psychiatric evaluation, neuropsychological assessment and the visit with the neurosurgeon). If the surgical candidates are treated with both L-dopa and DAs (either pramipexole or ropirinole) prior to surgery they will be asked to participate in the study. If they accept, they will undergo the first visit (about one month before surgery). During the first visit they will be administered scales and questionnaires evaluating both your motor and non-motor symptoms (i.e. apathy, mood, sleep) related to Parkinson's disease. This evaluation will last about 1 hour. Then, the patients will undergo surgery according to the standard of practice currently adopted at Toronto Western Hospital. For the first month after surgery their medication will be unchanged. After one month since surgery the patients will have your first programming visit. During this visit, the enrolled patients will be randomized either to join the L-dopa group or the DAs group (receiving either pramipexole or ropirinole). If they will be assigned to the L-dopa group you will gradually discontinue DAs, while if they will be randomized to join the DAs group you will gradually discontinue L-dopa. Then, every patient will be seen once a week for the subsequent 8 weeks to optimize both the stimulations settings and the medical treatment. After 3 month since surgery the enrolled patients will have the last visit of the study and will receive the same scales and questionnaires evaluating both your motor and non-motor symptoms (i.e. apathy, mood, sleep) related to Parkinson's disease. This evaluation will again last about 1 hour.