Directional PSA Versus STN DBS for TD-PD

Inclusion Criteria: * diagnosis of idiopathic Parkinson's disease * tremor-dominant subtype in the off-medication condition * modified Hoehn-Yahr scale of 2 to 4 in the off-medication condition * receiving regular anti-parkinsonian drugs for more than 6 weeks * good compliance and written informed consent provided Exclusion Criteria: * Atypical parkinsonism * History of stroke, encephalitis, neuroleptic uses, MRI scan with evidence of significant brain atrophy, lacunar infracts, or other conditions that might interfere with the intracranial surgery * Presence of cognitive, or psychiatric or other co-morbidities (e.g., dementia, epilepsy, cranial traumatism, brain tumor, schizophrenia, severe depression or bipolar disorder, personality disorder, etc.) that might interfere with the patient's ability to complete the evaluations or to provide informed consent * Presence of anatomical abnormalities in the target region * Clinically significant medical history that would increase pre-/post-operative complications * Other conditions considered by the investigators that might interfere with the surgery procedure, the follow-ups, and the interpretation of the data