Mapping of Human Cognition

Inclusion Criteria: * patients with medically refractory epilepsy who are scheduled to undergo or have previously undergone placement of sub-dural electrodes (including depth electrodes) to localize the site of seizure onset and to map the locations of critical language and motor regions * patients with epilepsy, brain tumors or cortically based vascular malformations (cavernous malformations or arterio-venous malformations) with lesions that are/were proximate to crucial brain regions, and who are scheduled to undergo or have previously undergone intra-op mapping of motor, visual or language function, or a Wada test, or maybe part of an awake craniotomy. * proficiency in English Exclusion Criteria: * Gross structural abnormalities (large hamartomata, tumors, large vascular malformations, very large diffuse malformations of cortical development) that may have impacted upon the location of critical brain areas. * Unable to participate in testing due to impaired cognition or mental retardation. * Cardiac pacemakers, intracranial aneurysm clips, or other potentially mobile implanted metallic devices * Patients with claustrophobia who cannot undergo an MRI scan without sedation