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
between 18 and 50 years old.
fluent in English.
able to provide written informed consent.
Unable to comply with study procedures or visits (including inability to schedule the second session within 10 business days of the first session).
Is pregnant or breastfeeding.
Has ears with indiscernible structures (e.g., cymba conchae, earlobe) due to congenital malformations, accidents, or physical alterations (e.g., "gauge", cartilage piercing).
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.