The objective of this study is to evaluate the neurobiological effects of hormone therapy (HT) in healthy early postmenopausal women. The studies proposed in this project seek to define the association between different hormone forms (estradiol only and progesterone only) versus placebo on brain functional measures. The functional measures will include the performance of the volunteers on a comprehensive neuropsychological testing battery, and the brain functional responses to episodic memory (verbal and non-verbal) challenges as well as emotional processing determined with functional magnetic resonance imaging (fMRI).