The cold plunge worked because it activated the vagus nerve. Now the wellness world is targeting it directly — with wearable devices, clinical trials showing PTSD remission, and techniques that don’t require ice.
The cold plunge had a good run. The tubs moved from pro sports recovery rooms into luxury spas, then into backyards and bathroom routines; the hashtags multiplied; Gwyneth endorsed it, Andrew Huberman explained it at considerable length, and eventually the thing became so ubiquitous that the conversation began to feel, for the first time, a little tired. What the cold plunge evangelists often didn’t mention, though, is that a significant part of what the ice bath was actually doing — the slowdown in heart rate, the wash of calm that follows the initial shock, the reset — was happening because cold exposure activates the vagus nerve. And now, it seems, the wellness world has decided to skip the middleman.
Bryan Johnson, the tech entrepreneur and longevity obsessive whose daily protocol became the subject of the 2025 Netflix documentary Don’t Die, wears a Pulsetto vagus nerve stimulator around his neck — a device about the size of a folded hand that delivers mild electrical current to the neck, targeting the vagus nerve directly. “If I wake up at night, I can put Pulsetto on and use this for 10 minutes,” Johnson said on social media. “It puts me back to sleep pretty quickly.” When the documentary aired last year, sales of the Pulsetto device increased by 300 percent on wellness retailer Healf.
Whether you’re obsessed with reversing aging like Johnson or not, stress, poor sleep, and anxiety have been dominating public health conversations for years, and the tools people are reaching for have moved steadily away from pharmaceuticals and toward devices, protocols, and techniques that work with the body’s existing hardware. The vagus nerve — the longest cranial nerve in the body, running from the brainstem through the neck and chest and into the abdomen — is, in a meaningful sense, the hardware everyone is now trying to tune.
What the vagus nerve actually does
“The vagus nerve touches pretty much every body system,” Tracy Centanni, PhD, a neuroscientist at the University of Florida, said in a campus publication. “I would never say that an approach is magical or a panacea, but I do see promise in vagus nerve stimulation for its ability to help with a lot of different things.” The nerve is the primary conduit of the parasympathetic nervous system — the branch responsible for the body’s rest-and-digest state, as opposed to the fight-or-flight response managed by the sympathetic branch. It carries signals in both directions: from the brain down to the organs, and from the organs back up to the brain, which is why vagal tone — the nerve’s baseline activity level — has been linked to everything from heart rate variability and immune function to mood regulation and digestion.
Stimulating it electrically is not new. The FDA approved surgical vagus nerve stimulation for drug-resistant epilepsy in 1997, and implantable devices have been used for treatment-resistant depression for decades since. What is new is the proliferation of noninvasive transcutaneous devices — Pulsetto, Apollo Neuro, Sensate, and others — that target the nerve through the skin of the neck or ear without surgery, and the growing body of research examining whether consumer-grade versions of the technology produce clinically meaningful effects. The answer, increasingly, appears to be: sometimes, and in ways that are genuinely surprising.
A 2025 systematic review and meta-analysis of randomized controlled trials found that transcutaneous vagus nerve stimulation produces clinically meaningful improvements in sleep quality. Separately, a 2025 Phase 1 clinical trial out of UT Dallas examined vagus nerve stimulation as a treatment for PTSD — nine patients, all with confirmed diagnoses, receiving a course of paired VNS and therapy. “In a trial like this, some subjects usually do get better, but rarely do they lose their PTSD diagnosis,” Dr. Michael Kilgard, the neuroscientist who led the trial, told UT Dallas News. “In this case, we had 100 percent loss of diagnosis. It’s very promising.” Benefits persisted at the six-month follow-up, which, in clinical terms, is a meaningful threshold.
From the cold tub to the wearable
The cold plunge connection is more than metaphor. When cold water hits the face or neck — activating the mammalian dive reflex — it triggers a cascade of vagal activity that slows the heart rate and shifts the autonomic nervous system toward parasympathetic dominance. This is the same shift that VNS devices are attempting to produce electrically. Cold exposure is, in effect, a blunt and indirect method of doing what a Pulsetto does with considerably more precision and considerably less suffering; the difference is that the cold tub delivers its vagal activation alongside a spike in cortisol and a few minutes of considerable discomfort, while the wearable delivers it while you sit on the couch. The appeal of the upgrade is not difficult to understand.
Dr. Mark Powers, a clinical psychologist at Baylor Scott & White Health who has worked with VNS in therapeutic settings, says VNS has changed his work dramatically.” He told UT Dallas News that the gold-standard treatments for PTSD have about an 85 percent response rate, “but that still leaves 15 percent of patients who don’t get better,” he said. “Soon we could have the option of VNS for people who don’t get better with cognitive behavioral therapy alone.” That is a clinical context, not a wellness one — but the research is the same research the consumer device industry is now pointing to, and the underlying neuroscience does not distinguish between the two applications.
Free techniques exist alongside the devices, and researchers take them seriously. Deep, slow diaphragmatic breathing — particularly the extended exhale — activates vagal efferents with each breath cycle. Humming and singing produce vibrations in the chest and throat that stimulate the nerve directly. Cold water splashed on the face triggers the same dive reflex as the full cold plunge, in less time and without the ice. These are not hacks; they are anatomically grounded interventions that have been studied to some degree, and most wellness medicine practitioners now include some version of them in their recommendations.
The consumer device market, meanwhile, has scaled quickly. Apollo Neuro, which uses vibration rather than electrical stimulation to influence the autonomic nervous system, is the most prescribed VNS-adjacent wearable in the United States; its clinical advisory board includes academic researchers, and it has several peer-reviewed studies in publication. Pulsetto uses direct electrical stimulation to the neck and has published data showing that 86 percent of users reported reduced anxiety after two weeks of use. Neither device is FDA-cleared as a treatment for anxiety or any other specific condition — that distinction belongs to the implantable surgical devices — but both have moved into a category the wellness industry has been building toward for years: technology that operates on the nervous system rather than around it.
“The good news is that you’re not going to do any harm,” Dr. Centanni said. “The worst thing that happens is it doesn’t work.”
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