Deep Brain Stimulation (DBS) uses electrical pulses sent through a lead (insulated wire) to help stop unwanted symptoms in a variety of brain diseases, including the tremor seen in patients with Essential Tremor (ET). The current standard lead allows this stimulation to spread out uniformly in all directions. As these diseases progress, however, the amount of electrical stimulation required to stop the symptom usually increases. This may become problematic because the increased electrical stimulation required for advanced symptoms may spread outside the desired targeted area, and effect other parts of the brain and causing unwanted side effects. A new type of DBS lead has been developed which can steer, or focus, the electrical stimulation in a given direction toward the desired target area and away from areas that would cause side effects. We would like to quantify the benefit seen in patients who have been switched from the traditional lead to this new directional lead.

Patients implanted with a DBS may experience unwanted side effects such as motor contractures, paresthesia, or dysarthria. This occurs when the electrical field of the stimulation spreads out beyond the targeted area. This is especially common in patients whose disease has progressed, and must use increasingly higher currents in order to regain control of their tremor. Unfortunately, because the electrical field affects neurons in a symmetrical sphere around the DBS, it is often impossible to reach the additional desired neuronal elements without simultaneously affecting equidistant brain regions responsible for side effects. For many of our advanced patients, this means choosing between a debilitating tremor or disabling side effects.The directional lead is a FDA and Health Canada approved DBS lead which features radially segmented electrodes which can selectively steer the electrical field in a predefined direction, orthogonal to the lead trajectory. This will allow DBS clinicians to steer current towards desired structural areas, while avoiding locations, which produce negative side effects.

Inclusion Criteria:

• Participants must have been implanted with the DBS
• Participants must have been diagnosed with Essential Tremor
• Participants must experience negative side effects from their DBS which limit control over their tremor
• Participants must be able to receive benefit from their stimulator, but at the cost of negative side effects

Exclusion Criteria:

• All individuals who meet criteria outlined in "inclusion criteria" may be eligible for this study