Activa Parkinson's Control Therapy and Essential Tremor Therapy uses one or two surgically implanted medical devices, similar to cardiac pacemakers, to deliver electrical stimulation to precisely targeted areas of the brain. Continuous stimulation of these areas blocks the signals that cause the disabling motor symptoms of the disease. As a result, many patients achieve greater control over their body movements, or have a significant reduction of tremors.   The Activa System consists of three implantable components: lead, extension, and neurostimulator. The neurostimulator which is placed in the chest wall, generates electrical pulses that are delivered through the extension to the lead to the defined target in the brain.