First introduced in the 1950s, thalamotomy is an invasive procedure, primarily effective for tremors such as those associated with Parkinson's Disease (PD), where a selected portion of the thalamus is surgically destroyed (ablated). Neurosurgeons use specialized equipment to precisely locate an area of the thalamus, usually choosing to work on only one side (the side opposite that of the worst tremors). Bilateral procedures are poorly tolerated because of increased complication and risk, including vision and speech problems. The positive effects on tremor are immediate. Other less destructive procedures are preferred, such as subthalamic deep brain stimulation (DBS), since this procedure can also improve tremor and other symptoms of PD.