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 4 weeks of at-home transcutaneous auricular neurostimulation (tAN) can reduce chronic pain after a stroke. We will recruit up to 24 participants with chronic post-stroke upper extremity pain. The goal is to determine if there is a pain reduction after ear stimulation.

This is an open-label pilot study firstly assessing safety and feasibility of a form of ear stimulation called transcutaneous auricular neuromodulation, or tAN, in women with postpartum depression (PPD). Secondly, we will be assessing the impact of at-home tAN on mood, empathy, and physiological markers of sympathetic activity in women with PPD. Participants will learn how to self-administer ear stimulation treatments in the lab before starting the at-home study. Over the course of one week, participants will self-administer ear stimulation treatments three times a day. Each treatment will last up to 60 minutes (1 hour) and there will be a break of at least 30 minutes in between treatments. The study team will ask participants to complete a group of questionnaires at the beginning and end of the study, as well as undergo heart rate variability (HRV) assessments and provide salivary samples. There will also be a smaller number of questionnaires completed electronically at the midpoint of the study. The questionnaires will ask questions about mental health symptoms that subjects may or may not be experiencing, including questions about mood, anxiety, and feelings towards their newborn.