The vagus nerve is the longest cranial nerve in the body. It stretches across the body to connect many organs, and like other cranial nerves, it carries signals to and from the brain to regulate basic body functions. Therapeutic techniques that stimulate the vagus nerve hold the potential to treat many disorders such as migraine, heart failure, and conditions impacting the muscles in the digestive system. The NIH Common Fund’s Stimulating Peripheral Activity to Relieve Conditions (SPARC) Program is accelerating the development of new therapeutic approaches by altering nerve activity. Traditional methods to stimulate the vagus nerve involve direct surgical implantation of electrodes beneath the skin, sometimes deep within the tissue directly around the nerve, but researchers have developed safer, non-invasive ways of stimulating the vagus nerve. One non-invasive technique works by stimulating a branch of the vagus nerve in the outer ear with an electrode placed on the skin. However, the exact nerve pathways involved and the optimal stimulation settings for this approach are not well understood.

A team of researchers from the SPARC program led by Dr. Eric Beaumont tested how stimulating the vagus nerve with electrodes placed on the outer ear of rats affected the responses of individual nerves in their brainstems. The researchers found specific stimulation settings that increased activity in certain areas of the brainstem that are known to respond to vagal activity, a sign that this approach could have therapeutic benefits. They also showed that the responses were comparable to traditional simulation using electrodes implanted directly on the nerve in the neck. Using non-invasive stimulation on the ear caused different nerve pathways to be activated than implanted electrodes. Understanding which nerves were activated can help tailor therapeutic approaches to specific conditions. This study demonstrates the ability of non-invasive vagus nerve stimulation to impact nerve activity. It further lays the groundwork for understanding the specific neuronal responses to this kind of vagus nerve stimulation in humans as well as providing more optimal settings for this non-invasive stimulation approach.

Reference: Owens MM, Jacquemet V, Napadow V, Lewis N, Beaumont E. Brainstem neuronal responses to transcutaneous auricular and cervical vagus nerve stimulation in rats. J Physiol. 2024 Aug;602(16):4027-4052. doi: 10.1113/JP286680. Epub 2024 Jul 19.