What Does The Vagus Nerve ACTUALLY Do?

In the past few years, one of the trendy it-girls of the social media wellness space has been the vagus nerve. Influencers claim that it impacts anxiety, depression, headaches, shoulder pain, racing heartbeat, being sensitive to lights and sounds, tummy problems, and basically everything about your body that might feel off. The good news is that they also claim you can fix these problems by doing stuff like resetting it or stimulating it or balancing it, which they will show you how to do in a TikTok video. All the talk about the vagus nerve can lead to a lot of confusion about what it is, what it does, and what exactly stimulating it accomplishes. And it turns out, while there’s plenty of nonsense out there, there may be a grain of truth to at least some of those wellness claims. [♪ INTRO] To kick us off, you don’t actually have a vagus nerve. You have two. Vagus nerves are cranial nerves, which all come in pairs. They also include your optic nerves, your facial nerves, and stuff like that. The vagus nerves are the tenth of twelve cranial nerves, so they’re also known as cranial nerve X. The name “vagus” comes from the Latin word for “wandering”, because these guys go everywhere. They meander through your body from your brain stem to the colon, with branches that connect your brain, chest, heart, lungs, and digestive tract. And oddly enough, the two vagus nerves aren’t mirror images of each other. The right and left nerves take different routes once they leave the neck, and only meet back up at the esophagus, close to your stomach. Not only that, but the individual branches of the nerves also take different paths on the right and left sides. For instance, there’s a pair of branches off the right and left called the recurrent laryngeal nerves, and the left one has to drop all the way down below the aorta just to loop up again to touch the larynx. Meanwhile on the right side, that branch is way shorter because it doesn’t take that detour. But despite there being two vagus nerves with different paths, people, including doctors, commonly just say “the vagus nerve” when talking about both of them, so if we say the singular instead of the plural, that’s why. And also, it’s our video, we can do what we want. The vagus nerve makes up about 75% of your parasympathetic nervous system, AKA your “rest and digest” system. The vagus nerves play a role in the things that just happen normally when we’re chilling out: digestion, breathing, resting heart rate, immune responses, and things like that. Some of the fibers of the vagus nerve take sensory information from the nerve endings in various organs and deliver it to the brain, and others take movement messages from the brain to those organs. So the vagus nerves are basically checking in with our organs and sending messages to the brain saying everything’s fine, which the brain responds to by sending messages saying “great, keep making digestive juices and keep the heart rate chill” back down to the organs. And along with that, the vagus nerve is also implicated in a lot of health problems and disorders. Vasovagal syncope happens when a vagus nerve near your heart decides to be a drama queen, causing a drop in blood pressure and fainting. Gastroparesis is when a damaged vagus nerve keeps the muscles in your gut from moving food out of your stomach. Damage to a vagus nerve can also mess with your heart rate, or cause problems with speaking or swallowing. But these disorders only happen when a nerve is physically damaged. So “resetting” it in the way talked about on social media is not an option for treatment. That said, vagus nerve stimulation is a very real thing. Specifically, there are these implantable devices that send electrical pulses to the brainstem via the left vagus nerve. It’s like a pacemaker, but for your brain. The left vagus nerve tends to be the focus, because the right vagus nerve is more directly connected to the heart, so there’s a higher chance that buzzing it could act like an actual pacemaker and mess with your heart rhythms. Vagus nerve stimulation has been approved by the FDA for some types of epilepsy, treatment-resistant depression, and to aid with physical rehabilitation after strokes. But even though we know that it can help with all those things… we don’t totally know why. For epilepsy, the working hypothesis is that zapping the vagus nerve disrupts the synchronized firing of neurons that happens during a seizure. One study found that about 50% of patients with a stimulator had half as many seizures as the people that didn’t. For depression, the best guess is that it impacts how the neurotransmitter noradrenaline gets passed between neurons. Another hypothesis is that it’s related to reducing inflammation by slowing down the production of immune system proteins called inflammatory cytokines. And as for stroke recovery, if a person’s vagus nerve is stimulated while they’re doing rehab exercises, we think it helps to create new pathways in the brain, helping to restore function in the patient’s limbs. Thanks to its anti-inflammatory properties, vagus nerve stimulation is currently being studied as a treatment for diseases that involve inflammation as well, like inflammatory bowel disease, rheumatoid arthritis, Alzheimer’s disease, intractable hiccups, and chronic pain. But most wellness influencers aren’t suggesting you talk to a doctor about invasive brain surgery that insurance doesn’t cover. At least, not that we could find when researching for this video. They’re talking about some more DIY approaches to stimulating your own vagus nerve. And yeah, there are ways to do that. But some of them can be really dangerous, and doctors are mixed about the safety of trying them at home. In a clinical setting, stimulating the vagus nerve is one of the first things a clinician might do for someone with a high heart rate, called tachycardia. The right vagus nerve connects to the sinoatrial node of the heart, which is our internal pacemaker. So stimulating the vagus nerve can tell the heart that it needs to slow down. There are a bunch of different vagal maneuvers that doctors can prescribe. With what’s called a Valsalva maneuver, you act like you’re exhaling, but without letting air escape your mouth or nose. Carotid sinus massage is exactly what it sounds like. Pushing on the carotid sinus in your neck. But this maneuver has a risk of serious complications, so it’s best left to trained professionals. The diving maneuver shows up pretty regularly on social media. I actually did it back in like, 2020, for our shorts. Hold your breath and then dunk your whole face into ice water for as long as you can. The holding your breath part is key here. Which I did not do correctly when I did it. Plus there are other options like stimulating the gag reflex, applying pressure to the abdomen, and even doing headstands. Overall, these maneuvers have a 20-40% success rate at getting heart rates back to normal. Which is great if you’re actually experiencing tachycardia. But if you aren’t, a sudden drop in heart rate can also cause some people to pass out. And the efficacy of all of these maneuvers has really only been studied in relation to tachycardia. So any claims that they can help with anxiety or other conditions aren’t backed up by the literature, and one study even tested them and found they weren’t actually effective for treating anxiety. But now, a message from our sponsors. Thanks to Brilliant for supporting this SciShow video! Brilliant is an online learning platform crafted by teachers, researchers, and professionals from MIT, Caltech, Duke, Microsoft, Google, and more. So when you dive in there, you’re bound to learn a lot. Each lesson is filled with hands-on problem solving, like puzzles, quizzes, and case studies. So you get to be actively involved in the learning process. You can start building understanding from the ground up at Brilliant.org/SciShow, or at the QR code, or at the link in the description. And you’ll get 20% off an annual premium Brilliant subscription, plus the first 30 days free. Okay, so what about those of us who don’t have medically diagnosed tachycardia? Do we need to do anything with our vagus nerve? Like, some influencers talk about maintaining your vagus nerve’s tone. But nerve tone doesn’t have anything to do with physical size or shape like we think of muscle tone. Vagal tone just refers to the activity of the nerve. So you can’t really tone your vagus nerve the way you can like, tone your arms. And low vagal tone doesn’t mean your nerve is floppy, it means it isn’t firing as frequently. There are a bunch of Instagram graphics out there talking about the signs and symptoms of vagus nerve dysfunction, and more specifically, low vagal tone. They may tell you that if you have tummy troubles, brain fog, low energy, anxiety, depression, or poor sleep, those are, according to these influencers, signs of vagal nerve dysfunction. And, I mean…maybe? But the thing about that list is that it’s pretty vague. And those symptoms can all be caused by a bunch of other things, too. So even if the vagus nerve is involved, just doing a ton of vagal maneuvers probably won’t get to the root of the problem. And anytime an influencer is telling you that a huge list of super general symptoms can be fixed with one weird trick, it’s worth being a bit skeptical. Medically speaking, diagnosing vagal nerve dysfunction doesn’t typically include mood, energy, sleep, or cognitive fuzziness. If your doctor suspects vagal nerve dysfunction, they’re much more likely to focus on your heart rate, breathing, EKGs, how you respond to exercise, and your gag reflex. Yeah, that last one sounds like an oddball, but it’s a pretty great litmus test for how your vagus nerve is doing. Because your vagus nerve connects to so many things in your throat, damage to the vagus nerve can cause difficulty swallowing, hoarse voice, or a messed up gag reflex. So if any of those things are happening, your doctor would know to investigate that pesky vagus nerve. But most of the conversation around the vagus nerve in the wellness space isn’t about swallowing or fainting. It centers on anxiety, stress response and resilience, and trauma. And there is some evidence that low vagus nerve activity can affect mental health, in mice at least. One study looked at how active the vagus nerves were in mice, based on how stress-sensitive they were. Researchers found that the vagus nerve was less active in the stress-susceptible mice than in the healthy, stress-free mice. And the vagus nerve stimulation in the stressed out mice helped return their vagus nerves to normal patterns and changed how they reacted in anxiety-provoking situations. Plus, the vagus nerve is potentially a critical component in something called the gut-brain axis, which has been getting more attention in the last two decades for its possible role in psychiatric diseases. Basically, the gut-brain axis is a kind of feedback loop that tells your brain how the gut is doing, and vice versa. And when one is out of whack, it can cause problems in the other. So when you’ve got a patient with a condition like depression, they’re more likely to have a gut issue too, and vice versa. And since the vagus nerve is the main connection between the two, the idea is that stimulating the vagus nerve might be a way to recalibrate the system, so to speak. Add that to the growing evidence for vagus nerve stimulation as a treatment for depression, and it’s definitely plausible that the vagus nerve could play a role in anxiety and stress, too. So there’s a whole host of things that influencers recommend you do for your vagus nerve, particularly if you’re feeling stressed or anxious. Things like forest bathing, sound baths, massages, and breathwork. Most of these things may actually work to stimulate your vagus nerve, but that sounds a lot more beneficial than it really is. See, the vagus nerve works in both directions. Activating it can tell your body to slow its breathing, but taking slow, deep breaths also activates the nerve. So anything that results in you taking those deep, slow breaths is likely going to stimulate your vagus nerve. It doesn’t matter if you choose sound bathing or forest bathing or yoga, as long as you slow your breathing, at least, not according to the evidence we have. That’s not to say that there’s no use for sounds with your vagus nerve. There’s some evidence that when sounds are paired with vagus nerve stimulation as part of physical rehab, it can help patients reduce their tinnitus symptoms or speed up motor recovery after a stroke. And for those of us who are looking for stress relief, influencers often suggest humming or singing, which is supported to some degree. The jury’s still out on why, though. The vagus nerve passes the larynx, which vibrates when you hum, so it’s possible that it’s stimulating the vagus nerve through those vibrations. Or, once again, it’s possible that the deep, sustained breaths you take while you hum are the secret sauce. Stimulating the vagus nerve endings might be the reason other suggested ways of impacting the nerve work, too. Acupuncture to your ears and applying cold temperatures to your neck also stimulate the vagus nerve, because the vagus nerves have so many endings in those areas. Basically, creating a sensation on the spots that are connected to the brain via the vagus nerve could potentially help, including your ears, neck, and lungs. Beyond that, other influencer-supported remedies like special massage oils, pillow mists, and bracelets don’t have anything in the way of direct scientific support. When it comes to the vagus nerve, there’s a lot of information out there. And it’s true that these humble cranial nerves have their fingers in a lot of the stuff that makes our bodies work. But while it can be tempting to blame every malady under the sun on a wonky nerve, the vagus nerve probably is neither the key to solving every one of your problems, nor the cause of every single woe you may have. So you can take some deep breaths. It’ll activate your vagus nerves. [♪ OUTRO]