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.

This is a research study to find out if mental health symptoms in patients admitted to the Institute of Psychiatry are affected by a form of ear stimulation called transcutaneous auricular vagus nerve stimulation, or taVNS. Participants will receive ear stimulation during their inpatient treatment at the Institute of Psychiatry. Participants will be randomly assigned to either receive ear stimulation for 1 day (up to 9 treatments over the course of a single day) or 3 days (up to 3 treatments per day), and will have a 50:50 chance of being in either group (like the flip of a coin). Each treatment will last up to 30 minutes 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. In addition, there are several questionnaires that will be completed daily while participants are receiving ear stimulation. Participants in the 1 day stimulation group will also receive 2 days of follow up questionnaires after the initial day of stimulation. The questionnaires will ask questions about mental health symptoms that subjects may or may not be experiencing, including questions about mood, anxiety, and sleep. The ear stimulation treatments will not interfere with the care subjects are receiving from the medical team. In order to qualify for this study, participants must be actively receiving inpatient care at the MUSC Institute of Psychiatry.

Trigeminal nerve stimulation (TNS) a form of nerve stimulation that is a safe and noninvasive way to activate the trigeminal nerve in the forehead. By stimulating the trigeminal nerve, we may be able to reduce sensitivity to various smells that are specifically sensed by the trigeminal nerve. This may help develop a new treatment for individuals that are over-sensitive to specific smells. The tools explored in this study are 1) Trigeminal Nerve Stimulation (TNS) and 2) Transcranial Direct Current Stimulation (tDCS). Both tools are non-invasive meaning that it does not involve any surgical procedures. TNS is a form of nerve stimulation that uses pulses of electricity delivered to stickers attached to the forehead. tDCS is a form of brain stimulation that uses sponges that are attached to your forehead which deliver a small, safe electrical current that activates your brain.

Participants (N=144) will undergo a baseline MRI visit to assess craving and brain function, and then be randomized to receive either: Active cTBS alone or Sham cTBS alone. Participants will return for a second MRI visit wherein brain function and cravings will be assessed immediately before and after active TBS or SHAM TBS. Participants will be contacted via phone over the following 3-weeks to assess mood and craving.