There are four potential target sites in the brain that may be selected for placement of stimulating electrodes: the internal segment of the globus pallidus (GPi), the subthalamic nucleus (STN), the pedunculopontine nucleus (PPN), and a subdivision of the thalamus referred to as Vim (ventro-intermediate nucleus). These structures are small clusters of nerve cells that play critical roles in the control of movement. Thalamic (Vim) stimulation is only effective for tremor, and usually does not work for the other symptoms of Parkinson’s disease, such as stiffness or slowness. Stimulation of the GPi or STN, in contrast, may benefit not only tremor but also other parkinsonian symptoms such as rigidity (muscle stiffness), bradykinesia (slow movement), gait problems, and dyskinesias. All three of these targets are now approved by the U.S. Food and Drug Administration (FDA), which oversees medical devices. The PPN is a new, investigational target that may be appropriate for patients with gait freezing, but there are currently few clinical studies of this. For most patients with Parkinson's disease, DBS of the GPi or STN is the most appropriate choice.