Monitoring study drug levels: Blood will be drawn at baseline (approximately 1400 hours) to assess cortisol levels. Blood will be drawn after each scan (approximately 1400 hours) to assess cortisol and phenytoin levels and to ensure adherence to the medications. We anticipate an increase in cortisol levels following administration of cortisol compared to baseline in subjects taking cortisol, and that therapeutic levels of phenytoin for seizures (10 to 20 mg/l) will be achieved.