Most centers require that patients have a brain imaging study (MRI or CT) to determine if there are problems in the brain that would pose excessive risk for surgery, unless one has been done within 1 year. Most centers also require an “on/off” evaluation. That is a formal neurological exam in the off-medication condition, following by re-assessment after a test dose of medication, by a movement disorder neurologist. For most patients, and especially those with a question of cognitive dysfunction, we request formal neuropsychological evaluation. All patients must have a blood test (mainly for blood clotting ability) and consultation with the anesthesiologists in the week prior to surgery.