This study will look for evidence that a virus called HHV-6B may be related to seizures and to a form of brain injury called mesial temporal sclerosis that is associated with seizures. The study will use new, more sensitive brain scans to try to detect brain regions that might be affected by the virus and will examine cerebrospinal fluid (CSF, the fluid that bathes the brain and spinal cord) for evidence of the virus as well.