In this research study, healthy participants will receive ear stimulation during brain imaging. Ear stimulation will involve the study team applying small electrodes to the outer part of your left ear and administering small amounts of electrical stimulation that may cause you to feel a "tickling" sensation on your ear. Participants will receive four, 8-min ear stimulation sessions in the scanner, and the order of the sessions is randomly assigned to you.

Knowledge gained from this study will help us better understand how stimulation of nerves in your ear turns on different parts of the brain.

This study is attempting to understand whether 30-minutes of a new ear stimulation technology can reduce pain in healthy individuals. Participants in this trial will attend two experimental visits, during which they will receive ear stimulation during the intravenous administration (I.V.) of either saline or naloxone. During each visit, the amount of thermal pain participants can tolerate will be determined before and after ear stimulation. Brain scans will also be collected before and after ear stimulation. Each visit should last about 3 hours.

The purpose of this study is to explore whether stimulating different outer parts of the ear using a non-invasive form of ear stimulation called transcutaneous auricular vagus nerve stimulation (taVNS) will create different brain activation images. We will recruit 24 healthy participants. The ear stimulation will be delivered while taking brain images using a magnetic resonance imaging (MRI) machine.