This study will examine how the drug methylenedioxymethamphetamine (MDMA) impacts response to different types of memory in humans compared to placebo. MDMA is an experimental drug and is illegal to possess outside of research; when sold illegally it is referred to as Ecstasy or Molly (material supposedly containing MDMA). MDMA may make it easier to face unpleasant memories and reduce anxiety, and it may do so in part by influencing response to memories. This study will enroll healthy adults who will need to come in for three visits over four days. At visit 1, participants will undergo a 1-hour startle test. The startle test measures eye-blink response to loud sounds. After this, the participant will also view different colored shapes presented on a computer monitor. While watching the computer monitor, the participant will experience several brief blasts of air directed at the throat, while eye-blink is measured with sensors under the eye. The following day at visit 2, participants will be randomized to receive placebo or 100 mg MDMA and will complete tasks similar to the ones completed the previous day. The researchers will measure pulse, blood pressure and temperature once before and seven times after receiving MDMA or placebo, and study participants will complete a questionnaire about their experience. Two days after receiving MDMA or placebo, participants will return for a third visit to complete similar tasks to previous visits. This study will also measure sleep through a sleep diary and actigraphy, which is a device worn on the wrist like a watch that records movement during sleep and lets researchers see how much sleep a person is getting.