Deep brain stimulation (DBS) is a surgical procedure for the treatment of Essential Tremor (ET). A novel approach to current DBS approaches is called coordinated reset DBS (CR-DBS) which uses different patterns of stimulation at lower currents and can address the limitations of traditional DBS that uses continuous high amplitude, high frequency stimulation. This study will evaluate the feasibility, safety and short-term efficacy of thalamic CR-DBS in upper extremity ET. The goal of this study is to evaluate the safety and short-term efficacy of thalamic CR- DBS in ET, including the acute (during CR-DBS) and carryover (following DBS cessation) effects, and compare these to those induced by clinically optimized T-DBS. To achieve our goal, a low-risk, two-phase clinical study will be conducted in patients with upper extremity (UE) ET. The first aim is to identify the spatial location and peak frequency of tremor related oscillatory activities in VIM (Phase I). The second aim is to compare the acute effects of thalamic CR-DBS to clinically optimized T-DBS (Phase II).