Effects of External Ear Stimulation on Pain Perception and Mood

Background: The vagus nerve runs from the brain to many organs. Stimulating it can affect the experience of pain. The nerve can be stimulated on the surface of the left ear. Researchers want to study how this stimulation affects the perception of pain. They also want to study how mood affects the experience of pain. Objective: To study the effects of mood and vagus nerve stimulation on the experience of pain. Eligibility: Healthy people ages 18 and older who are fluent in English Design: Participants will be pre-screened with a 15-minute phone call. Participants will have three 2-hour visits. At the screening visit, participants will be screened with: Medical and psychiatric history Physical and psychological exams Questionnaires about physical and psychiatric health and mood Urine tests A heat probe on the forearm. The temperature will be increased until it is painful but tolerable. Participants will have 2 testing sessions within 7 days. Before the testing, they cannot do the following: Eat, use nicotine, or exercise for at least 2 hours Drink alcohol for 24 hours Take certain medicines for 3 days Testing includes: Urine drug screening Left ear stimulation: In one session, the vagus nerve will be stimulated. In the other, an area of the ear away from the vagus nerve will be stimulated. This will be done with mild electric shocks that cause a tingling, pricking, or itchy feeling. Heat applied to the forearm until it is painful but tolerable Completing several forms on a computer or on paper about how they are feeling Monitors on the chest and a finger clip to monitor heart, breathing, and blood pressure