Directional Versus Nondirectional DBS for ET

Inclusion Criteria: * A tremor syndrome of bilateral upper limb action tremor with at least 3 years' duration Exclusion Criteria: * Patients who have decided not to receive DBS for control of their medication-refractory essential tremor. * Patients with secondary tremor (ie not Essential Tremor), such as side effects from medications, secondary to another identified neurologic disease (eg multiple sclerosis, -----Parkinson's disease, dystonia). * Prior history of deep brain stimulation. * Prior history of thalamotomy. * A history or signs of dystonia, ataxia or parkinsonism. * Task specific tremor. * Orthostatic tremor. * Patients with cardiac pacemakers, defibrillators, or neurostimulators. * Patients who require MRI, ECT, rTMS, or diathermy. * Subjects with other type of neurological disease or injury.