We will enroll 4 normal, healthy, adult male volunteers who will undergo screening tests (labs, EKGs, medical history, physical exam, and MRI of the brain) for safety. If eligible, they will return for three separate positron emission tomography (PET) scans. Over the course of the three study visits, each subject will receive eszopiclone (Lunesta), zolpidem (ambien) and a placebo in random order.