Elucidating the Temporality of Structural and Functional Connectivity Changes in Essential Tremor After Successful Deep Brain Stimulation to the Dentato-rubro-thalamic Tract

Inclusion Criteria: * the diagnosis of Essential Tremor, made by a movement disorder neurologist, where tremor is not secondary to any disease process or traumatic insult * distal appendicular tremor, with minimal proximal component * tremor refractory to multiple medication regimens and/or where the medications cause intolerable side effects * tremor judged to be severely impacting their quality of life. Exclusion Criteria: * significant neurological disorder * significant dementia or neurocognitive limitations as assessed by neuropsychiatry (when necessary) * severe psychiatric illness with suicidal ideations * previous surgery to destroy the target region of the brain * surgical contraindications to DBS * current major medical problems that affect brain anatomy,neurochemistry, or function, e.g., liver insufficiency, kidney insufficiency, cardiovascular problems, systemic infections, cancer, hypothyroidism, auto-immune diseases, and any current of history of brain disorder (seizure disorder, stroke, dementia, meningitis, encephalitis, degenerative neurologic diseases and head injury with loss of consciousness for any period of time) * family history of hereditary neurologic disorder, besides essential tremors ET * floating metallic objects in the body * pregnancy * alcohol or substance abuse/dependence in the past 6 months.