The purpose of this study is to investigate the brain activity associated with cognitive tasks (thinking, reasoning, remembering) in order to understand how the brain works during certain tasks and to improve treatment for diseases like dementia and attention deficit disorders. Cognitive (thinking) impairment may include poor memory function, poor attention span, or psychiatric disorders (ex: ADD, depression). The investigators are interested in the brain activity related to these issues, and want to investigate changes in brain activity while we record activity from specific areas of the brain. These recordings are in addition to clinical (routine or standard of care) recordings being performed to monitor for seizures and do not impact the clinical care.