I'm now going to tell you a tool that you can use when you're feeling less than energized, less than motivated, and when you need to exercise and you don't feel like doing it, and when you want to leverage exercise as a way to improve brain function and plasticity. It all involves the vagus nerve, and it involves an aspect of the vagus nerve that very few people are aware of, but in my opinion, is one of the coolest aspects of the vagus nerve.

It's at least as cool as vagal control over heart rate variability and auto-regulation, and it goes like this. There's a beautiful set of findings from a guy named Peter Strick at the University of Pittsburgh, who used these really cool methods for tracing connections between the brain and body to ask the question, what areas of the brain are communicating with our adrenal glands?

Our adrenal glands are two glands that sit atop your two different kidneys, so one atop each kidney and release, as the name suggests, adrenaline. Adrenaline is also called epinephrine. Your adrenal glands also release cortisol, but for sake of this discussion, let's just think about adrenaline released from your adrenals.

What he found through a bunch of experiments done in non-human primates, and that seemed to correspond very well to what we observe in humans as well, is that there are three general groups of brain areas. Motor activation areas, so what we call upper motor neurons. So these are the neurons in the brain that control the lower motor, neurons in the spinal cord that control the muscles of the body, as well as neurons within our brain that are involved in cognition and planning, and areas of the brain that are involved in emotion, that can communicate with the adrenals and cause them to release adrenaline.

Now that's great, but it sort of points to a pathway whereby, okay, you know you should exercise, you tell yourself you should exercise, you're emotional about it, and your adrenals release adrenaline and you exercise. Now that's interesting, but what's perhaps far more interesting is that the data from Strick Lab and other labs as well, shows that when we move the large muscles of our body, the adrenals release adrenaline, epinephrine.

Now epinephrine has an activating sympathetic nervous system, stimulatory effect, right? It tends to make the tissues of the body that are associated with movement and with so-called fight or flight, although again, fight or flight is kind of an extreme example, it tends to activate the organs of the body and make them more likely to be active.

It increases the probability that movement will occur, overall body movement. So when we move the large muscles of our body, our legs, and in particular our trunk muscles, we release adrenaline, that adrenaline activates the organs of our body and further makes it likely that we're going to move our musculature more.

But get this, adrenaline, epinephrine doesn't cross the blood brain barrier. So how does it increase our level of alertness in our brain, right? You don't want your body to be super active and your brain to be kind of sleepy. That's not good. That's not adaptive. It turns out that when the adrenals release adrenaline, it binds to receptors on the vagus nerve itself, those sensory axons that extend into the body.

There are receptors on those wires, right? Not all the receptors are at one end or the other, they're also on those axons. The adrenaline binds to the receptors on those axons and the vagus nerve in turn releases glutamate, an excitatory neurotransmitter in a structure in the brain called the nucleus tractus solitaris.

The neurons in what I'm just going to call the NTS for simplicity, in turn, activate neurons in a brain structure called the locus coeruleus. The locus coeruleus contains neurons that release what's called norepinephrine. And the neurons of locus coeruleus send their axons out very extensively across the brain in kind of a sprinkler system-like organization, such that when you move the large musculature of your body, you release adrenaline.

That adrenaline activates the tissues of your body, makes them more likely to move, also binds to receptors on the vagus. The vagus nerve in turn releases glutamate, an excitatory neurotransmitter in the NTS. The NTS then passes off that excitatory signal, like a bucket brigade off to the locus coeruleus.

The locus coeruleus dumps a bunch of norepinephrine into the brain and increases your levels of alertness. What this means is that the vagus nerve is central to the process of using physical activity to make your brain more alert. And we know that activation of locus coeruleus makes the brain areas that are involved in motivation and the propensity to move more higher in levels of activity.

In other words, if you're not feeling motivated to exercise, or you're not feeling alert enough, movement of the body that includes especially the legs, the large muscles of the legs, the quadriceps, hamstrings, et cetera, as well as the trunk muscles of the body, stimulate this pathway in a kind of dominoing effect that makes the likelihood and believe it or not, the desire to move much more likely.

This I've personally found to be an immensely useful piece of information because sure, I knew that sometimes I would go to the gym or I'd head out on a run and I wasn't feeling motivated, or I'd sit down to do some work and I'd feel kind of sleepy, despite the fact that I had slept pretty well the night before and eaten just fine and the room wasn't too warm, et cetera.

And I feel kind of lethargic. And I was like, what's going on here? And yes, I had the experience of sometimes, you know, doing a bit of a warmup, maybe some light calisthenics, maybe a few warmup sets or jogging for a little while, and then finding that my levels of alertness increased.

But I've also had just as often the experience of not feeling that motivation for physical activity or for cognitive activity come online, especially if I wasn't extremely interested in that activity or that thing that I was supposed to learn. You know, it's very easy to be excited when we want to do the activity or we want to learn the thing that we're supposed to be learning at a given moment or reading at a given moment.

This pathway is immensely useful to understand because it explains why it is that even when you're not feeling motivated, if you do some activity that, yes, is preceded by a bit of a warmup. So maybe, I don't know, you do some light calisthenics or you go on the treadmill for a few minutes walking, then maybe a little bit faster, that it can increase your levels of alertness and motivation.

But it especially explains how if you put in some effort that at the moment feels like a big exertion, your entire body and brain state shifts in a way that levels of motivation and energy to do more physical work or more cognitive work or both increases dramatically. And these are not small effects when they've been measured.

In fact, for all the talk that's out there in kind of pop psychology and in kind of pop neuroscience about the vagus being a calming pathway, all the neurophysiologists out there, and I know there aren't very many, but I'm friends with a lot of neurophysiologists, they'll all tell you that if they're doing a surgery or they're doing some sort of brain recording and the animal or person that they're doing the brain recording from is starting to drop into a state of deep parasympathetic activity, they're falling asleep or they need to be more alert, what do they do?

They stimulate the vagus. They stimulate the vagus nerve in order to wake up the brain. In fact, stimulating the vagus has been used to save people's lives when they are drifting too far down into deeper and deeper planes of anesthesia. So stimulating the vagus wakes up the brain. And the way to stimulate the vagus is by way of these receptors on the vagus nerve itself.

And the way to do that without an electrical stimulator, right? Because we're not talking about clinical conditions here, in order to increase levels of motivation, alertness, and focus for physical activity or cognitive activity and learning, et cetera, or simply to overcome lethargy and brain fog, is to do some sort of physical activity that includes the large musculature of your body.

These could be things like jumping. These could be things like actual resistance training. This could be running. This information really points to the idea of, of course, after a good warmup, doing more sprinting type activity, more strength type activity, you know, six repetitions or less where you're getting close to failure, this sort of thing to wake up the brain and body, as opposed to doing long rhythmic activity that's below the threshold of what would activate a lot of adrenaline from the adrenals.

So the idea is to get those adrenals to release adrenaline into your system. It won't cross the blood-brain barrier, but your vagus nerve provides this beautiful link between the body and brain to match levels of excitation from the body to the brain, and you can leverage that. So the idea is to get those adrenals to the body.