destruction of a part of the thalamus, in particular the ventralis intermedius, to suppress tremor in 80-90% of patients. If rigidity and akinesia are apparent, the subthalamis nucleus is then the site of ablation. A pallidotomy involves the destruction of the globus pallidus, in particular the globus pallidus interna, in patients with Parkinson's who have rigidity and akinesia. Because it is difficult to accurately measure the amount of tissue to be destroyed, tremors not uncommonly persist through multiple courses of surgery, since tissue is irreversibly damaged and removed and testing smaller areas of tissue is safer to prevent serious complications, such as a stroke or paralysis.. This method has been generally replaced by deep brain surgery. Deep brain stimulation Deep brain stimulation (DBS) is presently the most used method of surgical treatment because it does not destroy brain tissue, it is reversible, and it can be tailored to individuals at their particular stage of disease. DBS employs three hardware components: a neurostimulator, also called an implanted pulse generator (IPG), which generates electrical impulses used to modulate neural activity, a lead wire which directs the impulses to a number of metallic electrodes towards the tip of the lead near the stimulation target, and an extension wire that connects the lead to the IPG. The IPG, which is battery-powered and encased in titanium, is traditionally implanted under the collarbone, and is connected by the subcutaneous extension to the lead, which extends from outside the skull under the scalp down into the brain to the target of stimulation. The IPG, or the entire three-component system, are sometimes referred to as a brain pacemaker, due to the precedence and renown of cardiac pacemakers and similarities in the components of both types of systems. The preoperative targeting of proper implantation sites can be accomplished by the indirect and direct methods. The indirect method uses computer tomography, magnetic resonance imaging, or ventriculography to locate the anterior and posterior commissures and then employs predetermined coordinates and distances from the intercommissural line to define the target area. Subsequent histologically defined atlas maps can also be used to verify the target area. The direct method provides visualization and targeting of deep nuclei by applying stereotactic preoperative MRI, which unlike the indirect method, takes into account the anatomic variation of the nuclei's size, position, and functional segregation amongst individuals. Electrophysial functional mapping, a tool used in both methods to verify