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

* INCLUSION CRITERIA: All subjects must be: 1. between 18 and 50 years old. 2. fluent in English. 3. able to provide written informed consent. EXCLUSION CRITERIA: Overall exclusion criteria for the study 1. Unable to comply with study procedures or visits (including inability to schedule the second session within 10 business days of the first session). 2. Is pregnant or breastfeeding. 3. Has ears with indiscernible structures (e.g., cymba conchae, earlobe) due to congenital malformations, accidents, or physical alterations (e.g., "gauge", cartilage piercing). 4. Has a dermatological condition such as scars or burns, or has had a tattoo in the testing region within the previous four weeks that might influence cutaneous sensibility. 5. Women who consume more than 7 alcoholic beverages per week, and men who consume more than 14 drinks per week. 6. Has a current chronic pain condition or has had chronic pain in the past year (painful condition lasting more than six months). 7. Has a major medical condition, such as kidney, liver, cardiovascular, autonomic, pulmonary, or neurological problems (e.g., epilepsy) or a chronic systemic disease (e.g., diabetes). 8. Has or had psychiatric disorders such as major depression, major anxiety-related problems, post-traumatic stress syndrome, bipolar disorder, psychosis, or alcohol or substance abuse disorders as identified by the MINI International Neuropsychiatric Interview questionnaire, which will be administered as part of the screening procedure. 9. Has a medical condition potentially affecting cardiac functioning (e.g. arrhythmias, bradycardia \[\