Effects of External Ear Stimulation on Pain Perception and Mood

* 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 \[\<60 beats per min; determined during screening\]) or Raynaud s Disease or other medical condition affecting peripheral vascular sensitivity. 10. Is actively taking medications that are known to interfere with current measurements of pain or autonomic function. These include but are not limited to: opioids, antidepressants (such as tricyclic antidepressants, selective serotonin reuptake inhibitors, and serotonin norepinephrine reuptake inhibitors), anticonvulsants (including gabapentin and pregabalin), and blood pressure medications (including beta-blockers, calcium channel blockers, and ACE inhibitors). Participants who have used such medications in the last three months must have ceased taking them for at least one month or three medication half-lives (whichever is longer) in order to be included. 11. Baseline heat pain threshold exceeds 46 degrees C (to be determined after consent). 12. Has ever had acupuncture in or around any area of the ears. 13. NIH employees are subordinates, relatives, or co-workers of the investigators, or NCCIH DIR employees. Exclusion criteria for individual study session\* 1. Has consumed alcohol within 24 hours, shows signs of alcohol withdrawal syndrome, or has behavioral signs of intoxication. 2. Has exercised or eaten within two hours of testing session. 3. Used nicotinic substances (e.g., tobacco, gum, "e-cigarette") within 2 hours of testing. 4. Used topical pain-relieving creams in the testing area (e.g. methylsalicylate, capsaicin) within 24 hours of testing. 5. Used non-steroidal anti-inflammatory drugs (NSAIDS, e.g. aspirin, ibuprofen), acetaminophen, naproxen, sumatriptan within 3 days of testing. * To be determined during the pre-session screening. Participants that cannot refrain from these activities may have their session rescheduled up to two times. If the participant is found non-compliant during the second rescheduled appointment, he or she will be excluded from the study.