This study examines the relationship between a cerebral hemisphere and control of muscles on the same side of the body (ipsilateral control). One good way to study this relationship is to record electroencephalogram (EEG) activity directly from the cortical surface. Because patients with epilepsy who are surgical candidates are already undergoing monitoring with subdural and/or depth electrodes, they present an opportunity to study ipsilateral control. Studying the electrocorticographic (ECoG) activity associated with simple voluntary movement in such patients would not disturb ongoing monitoring of nearby areas of the brain, nor would it endanger the patients.