Healthy volunteers will have a 45-minute EEG (recording of the electrical activity of the brain) at the beginning of each menstrual cycle and each day during the menses. Women with epilepsy will have continuous EEG monitoring for 8 days, beginning 5 days before their menstrual period is expected. The continuous monitoring can be done on an outpatient basis, using a portable EEG recording device, or as an inpatient, with admission to the hospital for the 8 days of recording.