 This is a natural history study. In the premortem part of the study persons with SD, MTD, and VT and research volunteers will be screened for eligibility for the study. Brain MRI using a 3T scanner will be performed for volumetric reconstruction of gray matter on the first 60 participants in both the patient and research volunteer groups. In addition, high-resolution MRI using 7T scanner will be obtained to identify focal structural differences on individual basis in the same 20 SD patients compared to 20 controls. DTI will be conducted for visualization of white matter tracts in 25 subjects per group. The remaining subjects will only undergo the screening and anatomical MRI scans prior to brain donation. 