This 'electrical superhighway' helps to control everything from our breathing to our immune system. Could stimulating it transform physical and mental health?
I've made a cup of coffee, written my to-do list and now I'm wiring up my ear to a device that will send an electrical message to my brainstem. If the testimonials are to believed, incorporating this stimulating habit into my daily routine could help to reduce stress and anxiety, curb inflammation and digestive issues, and perhaps improve my sleep and concentration by tapping into the "electrical superhighway" that is the vagus nerve.
From plunging your face into icy water, to piercing the small flap of cartilage in front of your ear, the internet is awash with tips for hacking this system that carries signals between the brain and chest and abdominal organs. Manufacturers and retailers are also increasingly cashing in on this trend, with Amazon alone offering hundreds of vagus nerve products, ranging from books and vibrating pendants to electrical stimulators similar to the one I've been testing.
Meanwhile, scientific interest in vagus nerve stimulation is exploding, with studies investigating it as a potential treatment for everything from obesity to depression, arthritis and Covid-related fatigue. So, what exactly is the vagus nerve, and is all this hype warranted?
The vagus nerve is, in fact, a pair of nerves that serve as a two-way communication channel between the brain and the heart, lungs and abdominal organs, plus structures such as the oesophagus and voice box, helping to control involuntary processes, including breathing, heart rate, digestion and immune responses. They are also an important part of the parasympathetic nervous system, which governs the "rest and digest" processes, and relaxes the body after periods of stress or danger that activate our sympathetic "fight or flight" responses.
In the late 19th century, scientists observed that compressing the main artery in the neck - alongside which the vagus nerves run - could help to prevent or treat epilepsy. This idea was resurrected in the 1980s, when the first electrical stimulators were implanted into the necks of epilepsy patients, helping to calm down the irregular electrical brain activity that triggers seizures.
As more people were fitted with these devices, doctors began to spot an interesting pattern. "They noticed that even if the device didn't help their epilepsy, some of these patients started to have a better outlook on life," says Kevin Tracey, a professor of molecular medicine and neurosurgery at the Feinstein Institutes for Medical Research in Manhasset, New York. Today, vagus nerve stimulators are increasingly being investigated as an alternative to antidepressants in patients with treatment-resistant depression. Surgically implanted stimulators are also an approved treatment for epilepsy - although they only seem to work in a subset of patients. Using electrical stimulation to treat brain disorders such as epilepsy and depression makes intuitive sense - nerves and brain cells communicate using electricity, after all. However, in the late 1990s, Tracey and his colleagues made a surprising discovery. They were testing an experimental drug that they expected to dampen inflammation in rats' brains, but when they injected it, it dampened inflammation throughout the body.
This was puzzling, because the brain is physically separated from the rest of the body by the blood-brain barrier - a tightly packed layer of cells that regulates the passage of large and small molecules into the brain, to help keep it safe. Tracey and his colleagues tried severing the vagus nerve and repeated the experiment. This time, the drug's anti-inflammatory effects were confined to the brain.
It was an extraordinary discovery: conventional wisdom held that there was no connection between the nervous and immune systems - but the vagus nerve appeared to provide that link. Further research revealed that the brain communicates with the spleen - an organ that plays a critical role in the immune system - by sending electrical signals down the vagus nerve. These trigger the release of a chemical called acetylcholine that tells immune cells to switch off inflammation. Electrically stimulating the vagus nerve with an implanted device achieved the same feat.