For many years researchers have been trying to better understand the regulation of sleep and activity by studying circadian (daily) rhythms of human beings. It appears that the hormones estrogen, progesterone, and testosterone play a role in the regulation of circadian rhythm in animals. Researchers believe these hormones may also play a similar role in the regulation of human circadian rhythms. Little research has been conducted on how these hormones affect human circadian rhythms.

This study is designed to learn more about how specific hormones influence men and women's daily rhythms. This study will use women from another research study being conducted at the NIMH called, "The central nervous system effects of pharmacologically induced hypogonadotropic hypogonadism with and without estrogen and progesterone". Male subjects will be recruited from another NIMH study called, "The central nervous system effects of pharmacologically induced hypogonadotropic hypogonadism with and without testosterone replacement".

In order to test the possibility that gonadal steroids (estrogen, progesterone, and testosterone) change circadian rhythms and the sleep-wake cycle in humans, participants will undergo chronobiologic evaluations. The chronobiologic evaluations will look at sleep and rest periods, activity as measured by a wrist monitor, and 24 hour inpatient electroencephalograph (EEG), rectal temperature, and melatonin monitoring.