Inclusion Criteria:  Participants with epilepsy or brain tumors at UCSF undergoing surgical electrode implantation for seizure localization or for speech and language mapping and Participants with electrodes implanted in at least two regions of interest who are willing and able to cooperate with study tasks.  Exclusion Criteria:  Participants who lack capacity or decline to provide informed consent, Participants who have significant cerebral lesions or Participants with cognitive deficits that preclude reliable completion of study tasks.