The goal of this series of challenge studies is to examine the impact of menstrual cycle phase on cortical GABA response to administration of agents with either direct (benzodiazepines) or indirect (progesterone, fluoxetine) GABA modulating properties. While the impact of these agents on cortical GABA levels in women with premenstrual dysphoric disorder (PMDD) is of interest, this study is designed primarily for those women without a psychiatric illness.