Model-based Electrical Brain Stimulation

Inclusion Criteria: * Patients being evaluated for surgical treatment of medication refractory epilepsy and brain tumors will be studied. ONLY patients with electrodes implanted based on clinical criteria to locate their seizure focus will be studied. Most patients are healthy adults, outside of their epilepsy and/or brain tumor. * Subjects \>= 18 are only included in this study. * All patients with the above conditions and with implanted electrode arrays who are willing to participate and able to cooperate and follow research instructions will be recruited. However, analysis of research recording data will focus on those subjects with an IQ \>= 80, with no impairments of reading, naming, or articulation (to minimize confounds such as abnormal language processing that may affect their self-reporting with the questionnaire), and with no cerebral pathology affecting the cortical regions from which recordings are made. Exclusion Criteria: * Subjects \< 18 years old will be excluded from this study due to the high concordance of developmental disorders (cognitive and language-related) in pediatric epilepsies. * There will be no involvement of special classes of subjects, such as fetuses, neonates, pregnant women, children, prisoners, institutionalized individuals, or others who may be considered vulnerable populations. * Patients who are unable to give informed consent due to a brain disorder will be excluded from the study, as it is very likely that they would be unable to carry out the tasks demanded by the study.