Can the vagus nerve improve our mental state?

NEW YORK • In recent years, the vagus nerve has become an object of fascination, especially on social media. The vagal nerve fibres, which run from the brain to the abdomen, have been anointed by some influencers as the key to reducing anxiety, regulating the nervous system and helping the body to relax.

TikTok videos with the hashtag #vagusnerve have been viewed more than 72 million times and there are over 70,000 posts with the hashtag on Instagram. Some of the most popular ones feature simple hacks to "tone" or "reset" the vagus nerve, in which people plunge their faces into ice water or lie on their backs with ice packs on their chests.

Now, wellness companies have capitalised on the trend, offering products such as vagus massage oil, pillow mists and vibrating bracelets. These products claim to stimulate the nerve, but have not been endorsed by the scientific community.

Researchers who study the vagus nerve say that stimulating it with electrodes can potentially help improve mood and alleviate symptoms in those who suffer from treatment-resistant depression, among other ailments. But are there other ways to activate the vagus nerve? Who would benefit most from doing so? And what is the vagus nerve, anyway? Here is a look at what we know so far.

The term "vagus nerve" is shorthand for thousands of fibres. They are organised into two bundles that run from the brain stem down through each side of the neck and into the torso, branching outwards to touch our internal organs, said Dr Kevin Tracey, a neurosurgeon and president of the Feinstein Institutes for Medical Research, Northwell Health's research centre in New York.

Imagine something akin to a tree, whose limbs interact with nearly every organ system in the body. The word "vagus" means "wandering" in Latin.

The vagus nerve picks up information about how the organs are functioning and sends information from the brain stem back to the body, helping to control digestion, heart rate, voice, mood and the immune system.

For those reasons, the vagus nerve - the longest of the 12 cranial nerves - is sometimes referred to as an information superhighway.

Dr Tracey compared it with a transatlantic cable.

"It's not a mishmash of signals," he said. "Every signal has a specific job."

Scientists began examining the vagus nerve in the late 1800s to investigate whether stimulating it could be a potential treatment for epilepsy. They later discovered that a side effect of activating the nerve was an improvement in mood. Today, researchers are examining how the nerve can affect psychiatric disorders, among other conditions.

Evidence indicates that stimulating the vagus nerve can help people with epilepsy, diabetes, treatment-resistant depression and post-traumatic stress disorder (PTSD) - as well as inflammatory autoimmune conditions such as Crohn's disease or rheumatoid arthritis.

"It can sound sort of magical with all the things it does," said Dr Eric Porges, an assistant professor in the department of clinical and health psychology at the University of Florida who studies the vagus nerve. He added that "our understanding of the vagus nerve continues to grow in richness and depth".

In the early 2000s, researchers started to show that vagus nerve stimulation could help some patients who were severely depressed and had not responded to other treatments.

A wave of studies followed.

By 2005, the United States Food and Drug Administration had approved implantable pulsegenerating devices that sent electrical signals to the vagus nerve, for use in patients with treatmentresistant depression. Similar devices have also been approved for obesity - to help control feelings of hunger and fullness - and for the treatment of epilepsy.

Researchers are now recruiting patients for the largest clinical trial to date examining to what degree vagus nerve stimulation may help patients with depression who have been unable to find relief with other treatments.

Implanting a device may be especially helpful for those with bipolar depression because so few treatments exist for them, said Dr Scott Aaronson, one of the senior psychiatrists involved in the clinical trial and chief science officer of the Institute for Advanced Diagnostics and Therapeutics.

Implanted vagus nerve stimulation is not accessible for most people, however, because insurers have declined to pay for the procedure, with the exception of Medicare recipients participating in the latest clinical trial.

Dr Tracey's research, which uses internal vagus nerve stimulation to treat inflammation, may also have applications for psychiatric disorders such as PTSD, said Dr Andrew Miller, director of the Behavioural Immunology programme at Emory University, who studies how the brain and the immune system interact and how those interactions can contribute to stress and depression.

PTSD, he said, is characterised by increased measures of inflammation in the blood, which "can influence circuits in the brain that are related to anxiety".

The activity of the vagus nerve is difficult to measure directly, especially given how complex it is. But because some vagus nerve fibres connect with the heart, experts can indirectly measure cardiac vagal tone - or the way in which your nervous system regulates your heart - by looking at your heart-rate variability, the fluctuations in the amount of time between your heartbeats, on an electrocardiogram.

An abnormal vagal tone - one in which there is very little heart-rate variability - has been associated with conditions such as diabetes, heart failure and high blood pressure. A high variability between heartbeats may signify an ideal vagal tone.

Holding your breath and submerging your face in cold water can trigger the "diving reflex", a response that slows the heartbeat and constricts blood vessels. Some people who have tried it report that it has a calming effect and can even reduce insomnia. Others wrap an ice pack in cloth and place it on their chest to relieve anxiety.

But Dr Tracey urged caution, adding that it is difficult to properly assess the risks and benefits without clinical data.

"I would not advise anyone to do any intervention without checking with their physician," he said. "For wellness, try to maintain high vagus nerve activity through mindfulness, exercise and paced breathing. These are all very good for you."

NYTIMES