Navigating the vagus nerve: from former explorations to novel therapeutic frontiers
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When experimenting on a cat in 1938, Bailey and Bremer first documented that electrical pulses into the longest cranial nerve led to changes in brain activity in the cerebral cortex. As more scientists cottoned on to the importance of the vagus nerve, research into vagus nerve stimulation evolved until 1988, when neurologist James Penry and neurosurgeon William Bell took a leap of faith at the Wake-Forest Bowman Gray School of Medicine in the United States. For the first time, a vagus nerve stimulator was implanted in a human.
Today, mention of the vagus nerve swims within pop-psychology and alternative health circles. It is generally believed that the nerve is responsible for bringing calm to the body and brain; keen health gurus and yoga instructors will promise states of inner tranquillity upon carrying out whichever vagus-stimulation service they’re conveniently selling. Scientists, however, rue this rudimentary explanation of a nerve that has a truly complex set of functions. So, what is the vagus nerve and what does science say about its role in relaxation?
The vagus, cranial nerve ten, is the only cranial nerve that extends far beyond the head and neck area, reaching all the way into our gut. True to its Latin name, the ‘wanderer’ winds from our brain stem down through our heart, lungs, and abdomen, and involves itself along the way in our breathing, heart rate, and digestion. Tagged an ‘information superhighway’, 80% of fibres in the vagus transmit ascending messages to the brain, playing a key role in our ‘interoception’ or ability to sense our inner states. The relaxation reputation earned by the nerve is due to it being the main component of our parasympathetic system. Parasympathetic function allows us to ‘rest and digest’ when threats in our environment subside. It acts in opposition to our ‘fight or flight’ sympathetic system, orchestrating a state of safety by reducing our heart rate and blood pressure whilst kickstarting digestion. Beyond this, vagal fibres travel to our ears for audition and to our mouths, allowing us to speak and swallow. All in all, an impressive bodily resume.
Would it not then be logical to assume that vagus nerve stimulation would induce our parasympathetic state, leaving us feeling oh-so-good? As you might have expected, it’s not that straightforward. A simple stimulation doesn’t equal spa-day calm due to the ranging functions of the nerve, as zapping different parts will activate different responses.
Clinically, vagus nerve stimulation is carried out as an adjunctive therapy on patients who are not responsive to other forms of treatment. It was in 2005 that the Food and Drug Administration approved vagus nerve stimulation for patients with treatment-resistant depression. By implanting an electrode near the collarbone with a wire running into the vagus, the battery-run circuit chips into brain activity. In studies with over 200 patients, after a year of stimulation, symptoms improved by 20-30%, with some patients claiming full recovery. Doctors believe that the electrical impulses affect norepinephrine and serotonin, neurotransmitters which are important to our mood. It may come as a surprise that these depression interventions often use vagus nerve stimulation to increase alertness and arousal in our sympathetic system to relieve depression, rather than inducing calmness. Vagus nerve stimulation can even be used to jolt people undergoing surgery awake when drifting towards a comatose state.
Beyond its established use in treating depression as well as in drug-resistant epilepsy to reduce seizures and improve mood, vagus nerve stimulation is being investigated in relation to rheumatoid arthritis, migraines, chronic cluster headaches, and the inflammatory bowel disease, Crohn’s. A recent journal article released in January in The International Journal of Tissue Repair and Regeneration outlined its potent pain-relieving and anti-inflammatory effects, arguing for its potential in improving chronic wound healing.
Fear not; all is not lost for those of you who utilise non-medical vagus nerve relaxation techniques. There is some credible evidence that engaging with your vagus nerve through practices such as breathwork can bring about states of inner calm. Scientists simply don’t like to oversell one aspect and understate the rich role of our vagus; the nerve is a champion at relaxation but is also the up-and-coming underdog in many other therapeutic areas.