Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health, and performance. My name is Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. This podcast is separate from my teaching and research roles at Stanford. Today, we're talking all about emotions. Emotions are central to our entire experience of life. Whether or not we're happy or sad or depressed or angry is our life experience. And yet I think with all the importance that we've placed on emotions, very few people actually understand how emotions arise in our brain and body. And I mentioned brain and body, because as you'll see today, emotions really capture the brain-body relationship. We cannot say that emotions arise just from what happens in our head. The other thing about emotions is that there's no real agreement as to what's a good emotion or a bad emotion. Today, we're going to talk about the biology of the chemicals and pathways that give rise to emotions in the context of food and nutrition. The discussion around emotions has a long and rich history going back to Darwin and even long before Darwin. You know, this is a conversation that philosophers and scientists have been having for hundreds, if not thousands of years. You know, the idea that Darwin put forth and that was really attractive for about the last hundred years was that emotions are universal and that some of the facial expressions around emotion are universal. And other people have, you know, capitalized on that idea. And to some extent it's true. I mean, I think that the two most robust examples of that would be when we see something or we smell something or we taste something that we like, there does tend to be a postural leaning in. We tend to inhale air at that time. We tend to bring in more of whatever chemical substance is there. So we tend to do these and, you know, and kind of lean in closer to things that are attractive to us. And when we see and experience things that we don't like, sometimes it's a mild aversion. We just kind of lean back or look away. Other times, it's an intense aversion of disgust and we tend to cringe our face. We tend to avoid inhaling any of the chemicals. This probably has roots in ancient biological mechanisms that are to prevent us from ingesting things that are bad for us, chemical compounds and tastes that might be poisonous. So much of the foundation of any discussion about emotion has to center around this kind of push pull of attraction to things or aversion from things. Now that's a very basic way of thinking about emotions, but if you think about it, it works for a lot of different circumstances. And in the brain, everywhere from the deep circuits of the brain to the more kind of what we call higher order, evolved centers of the brain, we have this push pull thing. We're either, in a previous episode, I talked about go, the circuits that allow you to emphasize action, and then no-go circuits, the circuits in the basal ganglia that allow you to de-emphasize action and prevent action. And so we can break down the discussion about emotions into these simpler versions of themselves. But at the core of that, of attraction or aversion, is an important theme that you might realize already, but most people tend to overlook, which is that there's an action there. You're either moving forward or you're moving away from something. The brain has a body so that the organism can move. And the body has a brain so that the organism, you, can move toward or away from things that you deem to be good or bad for you. So there are circuits in the brain for aversion and for attraction toward things, and the body is governing a lot of that. And so immediately in this conversation, I want to raise an important point, which is about a nerve pathway that many, many people have heard of that gets discussed all the time, and that is one of the most kind of oversold for the wrong reasons and undersold, unfortunately, for its real power, which is the vagus nerve. So the vagus nerve is one, not the only, but one way in which our brain and body are connected and regulates our emotional states. So what is the vagus nerve? Vagus is the 10th cranial nerve, which basically means that the neurons, the kind of the control center of each of those neurons in the vagus lives just kind of near the neck, right? And a branch of the vagus goes into the brain. The other branch goes into the periphery, but not just the gut. It goes into the stomach, the intestines, the heart, the lungs, and the immune system. So the way to think about the vagus is the same way I would think about the eyes. The eyes are looking at colors, they're looking at motion, they're looking how bright it is. And each one of those things, those features is telling the brain something different. So the brain can decide when to be awake or asleep, whether or not it's looking at somebody attractive or unattractive. The vagus nerve is also analyzing many features within the body and informing the brain of how to feel about that and what to do. So a really good example that I think is an exciting one is as it relates to sugar. So we all know that sweet things generally taste good. So that makes sense, right? You eat something, it tastes sweet, you want more of it. Well, it turns out that it's much more interesting than that. When you eat something sweet, within your stomach, you have cells, neurons, that sense the presence of sugary foods, independent of their taste, and signal to the brain. So those sensors, those neurons, send information up the vagus to your brain, goes through a series of stations, and then you release dopamine, this molecule that makes you want more of whatever it is that you just ingested. In fact, this pathway is so powerful that they've done experiments where they completely numb all the taste and feeling in somebody's mouth.