Detailed surgical procedure has been presented in our previous study.17 (link),22 (link) In brief, all patients underwent pre-operative contrast enhanced volumetric T1 and T2-weighted magnetic resonance imaging (MRI) of the brain. On the day of surgery, Cosman–Roberts–Wells (CRW) frame (Radionics, Burlington, MA, USA) were applied to the skull under local anesthesia, and a full head computed tomography (CT) scan was obtained using 1-mm slice thickness. CT and MRI images were fused using Medtronic StealthStation FrameLink software. The targets of the STN were calculated based on a stereotactic atlas. The coordinates of the target point of the STN were 12 mm lateral, 1 mm posterior, and 4 mm inferior to the mid-commissural point. The recording tracks were made in a trajectory with a 12° angle lateral from the vertical line and approximately 60° from the intercommissural line. A full-head CT scan was obtained using 1-mm slice thickness 1 day after surgery and fused with MRI images for target planning before surgery. Lead location in the STN was clearly indicated and the trajectory length of microelectrode recording was confirmed indirectly.