Dr. Kevin Tracey

I think we're going to help millions of people.

There's been experience, but to my review of the literature, and I'm speaking to the world's expert on the review of the medical literature, so that makes myself nervous.

But that being said, my review of the literature, I am unable to find for handheld devices applied to the skin,

any evidence that any of them directly stimulate the vagus nerve.

So as biomedical engineers, we've tried to do it in my lab and we've tried to do it in volunteers and we've worked with biomedical engineers.

If you put electricity on the skin of a human being or a large animal,

The vagus nerve in humans, in the neck where you pointed, is deep in the neck.

It's wrapped in its own sheath with the carotid artery.

It's underneath several layers of fascia.

It's underneath the platysma muscle.

It's underneath the skin.

Electrocurrent doesn't travel like a laser beam where you point the thing when you put it on your skin.

It doesn't work that way.

And so...

It's okay to call things vagus nerve stimulators after they've gone through FDA trials, but it doesn't mean they are vagus nerve stimulators.

There's one place the vagus nerve sends a branch to the skin, and that is in the cartilage of the external ear called the simpacantia, which is the part of your ear that looks like a seashell around the open ear, simpacantia.

Now, if you electrically stimulate the Simba concha with some sort of device, a TENS unit or something, then arguably you've stimulated the vagus nerve because you've stimulated the sensory fibers traveling from that cartilage.

You know why it's there, right?

This vagus, it's a vestigial branch of the vagus nerve that used to innervate evolutionarily the cartilaginous gills of fish.

And so it dragged the nerve with it when that cartilage became the cartilage of the external ear.