Evaluation of Directional Stimulation During the Implantation of Deep Brain Stimulation (DBS) Leads

Inclusion Criteria: * Subject is indicated to undergo DBS for Parkinson's disease or Essential Tremor according to criteria of the Study site * For Parkinson Disease: * Person is between 18 and 75 years of age * Established diagnosis of idiopathic Parkinson's disease with progression of symptoms for a minimum of 2 years. * Person has a history of at least 30% improvement on the Unified Parkinson's Disease Rating Scale with therapy in L-dopa (levodopa) * Weak control of symptoms by dopaminergic therapy (off phenomenon, fluctuations on / off, dyskinesia on) * For Essential Tremor: * Person is between 18 and 80 years of age * Established diagnosis of Essential Tremor for a minimum of 2 years * Functional disability due to tremor was not adequately controlled by medication for at least 3 months prior to implant. * Person has given his/her written consent Exclusion Criteria: * Person suffering from an active major psychiatric disorder * Mattis Dementia Rating Scale score \<130 or otherwise not capable of discernment * Presence of major co-morbidity or medical condition that may affect participation to the study * Presence of an electrical or electromagnetic implant (e.g., cochlear implant, pacemaker) * Person with a previous surgery for the treatment of Parkinson's disease or Essential Tremor * Person with a previous brain ablation procedure * Person who suffers from epilepsy * Person who is pregnant: a pregnancy test will be performed in women of childbearing age * Person with coagulopathies * Abuse of drugs or alcohol