Tonic Pain and Transauricular Vagal Nerve Stimulation

Exploration of the Effect, and Their Duration, of Different Frequency Transcutaneous Auricular Vagal Nerve Stimulation on Sensory Perception.

This study aims to explore the effect of burst-taVNS (electric stimulation of the concha cymba) on tonic (capsaicin-induced skin pain) and acute (pressure pain sensitivity) experimental pain and cardioception. Primary outcomes include pain intensity. Secondary outcomes include sensory thresholds, resting heart rate (EKG), pupillary measurements and conditioned pain modulation.

Across 3 visits, each lasting around 2.5hours, burst-taVNS (electrical stimulation of the concha cymba) will be compared to active-control (electrircal stimulation of the earlobe) and sham (no current) stimulation, two gold-standard controls. Assessments of outcomes will occur before capsaicin application and before, twice during and after electrical ear stimulation.

Inclusion Criteria:

• Healthy
• Speak and understand English
• 18-60 years old.

Exclusion Criteria:

• Pregnant and/or breastfeeding
• Regular use of cannabis, opioids or other drugs
• Current or previous neurologic, musculoskeletal, mental, or other illnesses (e.g., brain or spinal cord injuries, degenerative neurological disorders, major depression, cardiovascular disease, chronic lung disease, etc.)
• Current regular (once or more a week) use of analgesic medication or other medication which may affect the trial (including paracetamol and NSAIDs)
• Recent history of acute pain particularly in the lower limbs
• Abnormally disrupted sleep in 24 hours preceding experiment
• Contraindications to electric stimulation application (history of epilepsy, metal implants in head or jaw, etc.)
• Lack of ability to cooperate
• Contraindications for capsaicin including an intolerance chili consumption and burns or wounds to the application site.