Essentials: How Smell, Taste & Pheromones Shape Behavior

**Andrew Huberman** (0:00)
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.
I'm 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 going to talk about chemical sensing. We're going to talk about the sense of smell, our ability to detect odors in our environment. We're also going to talk about taste, our ability to detect chemicals and make sense of chemicals that are put in our mouth and into our digestive tract. And we are going to talk about chemicals that are made by other human beings that powerfully modulate the way that we feel, our hormones and our health. Now that last category are sometimes called pheromones. However, whether or not pheromones exist in humans is rather controversial. There actually hasn't been a clear example of a true human pheromonal effect. But what is absolutely clear, what is undeniable is that there are chemicals that human beings make and release in things like tears onto our skin and sweat and even breath that powerfully modulate or control the biology of other individuals. There are things floating around in the environment, which we call volatile chemicals. So when you actually smell something, like let's say you smell a wonderfully smelling rose or cake, yes, you are inhaling the particles into your nose. They're literally little particles of those chemicals are going up into your nose and being detected by your brain. Other ways of getting chemicals into our system is by putting them in our mouth.
By literally taking foods and chewing them or sucking on them and breaking them down into their component parts. And that's one way that we sense chemicals with this thing, our tongue. So these chemicals, we sometimes bring into our body, into our biology through deliberate action. We select a food, we chew that food and we do it intentionally. Sometimes they're coming into our body through non deliberate action. We enter an environment and there's smoke and we smell the smoke and as a consequence, we take action. Sometimes, however, other people are actively making chemicals with their body. Typically, this would be with their breath, with their tears, or possibly, I want to underscore possibly, by making what are called pheromones, molecules that they release into the environment, typically through the breath, that enter our system through our nose, our eyes, or our mouth that fundamentally change our biology. I'll just give an example, which is a very salient and interesting one that was published about 10 years ago in the journal Science, showing that humans, men in particular in this study, have a strong biological response and hormonal response to the tears of women. What they did is they had women, and in this case, it was only women for whatever reason, cry and they collected their tears. Then those tears were smelled by male subjects or male subjects got what was essentially the control, which was the saline. Men that smelled these tears that were evoked by sadness had a reduction in their testosterone levels that was significant. They also had a reduction in brain areas that were associated with sexual arousal. They actually recruited subjects that had a high propensity for crying at sad movies, which was not all women. What they were really trying to do is just get tears that were authentically cried in response to sadness, as opposed to putting some irritant in the eye and collecting tears that were evoked by something else, like just having the eyes irritated. Nonetheless, what this study illustrates is that there are chemicals in tears that are evoking or changing the biology of other individuals. Now, I didn't select this study as an example, because I want to focus on the effects of tears on hormones per se, although I do find the results really interesting. I chose it because I wanted to just emphasize or underscore the fact that chemicals that are made by other individuals are powerfully modulating our internal state, and that's something that most of us don't appreciate. I think most of us can appreciate the fact that if we smell something putrid, we tend to retract, or if we smell something delicious, we tend to lean into it. But there are all these ways in which chemicals are affecting our biology, and interpersonal communication using chemicals is not something that we hear that often about, but it's super interesting. So let's talk about smell and what smell is and how it works. I'm going to make this very basic, but I am going to touch on some of the core elements of the neurobiology. So here's how smell works. As many of you know, I've been taking AG1 daily for more than 13 years. However, I've now found an even better vitamin mineral probiotic drink. That new and better drink is the new and improved AG1, which just launched this month. This next gen formula from AG1 is a more advanced clinically backed version of the product that I've been taking daily for years. It includes new bioavailable nutrients and enhanced probiotics. The next gen formula is based on exciting new research on the effects of probiotics on the gut microbiome. 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But with each passing year, and by the way, I'm turning 50 this September, I continue to feel better and better. And I attribute a lot of that to AG1. AG1 uses the highest quality ingredients and the right combinations. And they're constantly improving their formulas without increasing the cost. So I'm honored to have them as a sponsor of this podcast. If you'd like to try AG1, you can go to drinkag1.com/huberman to claim a special offer. Right now, AG1 is giving away an AG1 welcome kit with five free travel packs and a free bottle of vitamin D3 K2. Again, go to drinkag1.com/huberman to claim the special welcome kit with five free travel packs and a free bottle of vitamin D3 K2. Smell starts with sniffing. Now that may come as no surprise, but no volatile chemicals can enter our nose unless we inhale them. If our nose is occluded or if we're actively exhaling, it's much more difficult for smells to enter our nose, which is why people cover their nose when something smells bad. Now the way that these volatile odors come into the nose is interesting. The nose has a mucosal lining mucus that is designed to trap things, to actually bring things in and get stuck there. At the base of your brain, so you could actually imagine this or if you wanted, you could touch the roof of your mouth right above the mouth, about two centimeters is your olfactory bulb. The olfactory bulb is a collection of neurons and those neurons actually extend out of the skull, out of your skull, into your nose, into the mucosal lining. So what this means in kind of a literal sense is that you have neurons that extend their little dendrites and acts only like things, their little processes as we call them, out into the mucous and they respond to different odorant compounds. Now the olfactory neurons also send a branch deeper into the brain and they split off into three different paths. So one path is for what we call innate odor responses. So you have some hardwired aspects to the way that you smell the world, that were there from the day you were born and that will be there until the day you die. These are the pathways and the neurons that respond to things like smoke, which as you can imagine, there's a highly adaptive function to being able to detect burning things because burning things generally means lack of safety or impending threat of some kind. It calls for action. And indeed these neurons project to a central area of the brain called the amygdala, which is often discussed in terms of fear, but it's really fear and threat detection. You also have neurons in your nose that respond to odorants or combinations of odorants that evoke a sense of desire and what we call appetitive behaviors, approach behaviors that make you want to move toward something. So when you smell a delicious cookie or some dish that's really savory that you really like, that's because of these innate pathway, these pathways that require no learning whatsoever. Now, some of the pathways from the nose, these olfactory neurons into the brain are involved in learned associations with odors. Many people have this experience that they can remember the smell of their grandmother's home or the smell of particular items baking or on the stove in a particular environment. Typically, these memories tend to be of a kind of nurturing sort of feeling safe and protected. But one of the reasons why olfaction, smell, is so closely tied to memory is because olfaction is the most ancient sense that we have. So we have pathway for innate responses and a pathway for learned responses. And then we have this other pathway. And in humans, it's a little bit controversial as to whether or not it sits truly separate from the standard olfactory system or whether or not it's its own system embedded in there, but that they call the accessory olfactory pathway. Accessory olfactory pathway is what in other animals is responsible for true pheromone effects. For example, in rodents and in some primates, including mandrills, if you've ever seen a mandrill, they have these like big, big noses things. You may have seen them at the zoo. Look them up if you haven't seen them already, M-A-N-D-R-I-L-S, mandrills. There are strong pheromone effects. Some of those include things like if you take a pregnant female rodent or mandrill, you take away the father that created those fetuses or fetus, and you introduce the scent of the urine or the fur of a novel male, she will spontaneously abort or miscarry those fetuses. It's a very powerful effect. Another example of a pheromone effect is called the Vandenberg effect named after the person who discovered this effect, where you take a female of a given species that has not entered puberty, you expose her to the scent or the urine from a sexually competent, meaning post-puberty male, and she spontaneously goes into puberty earlier. So something about the scent triggers something through this accessory olfactory system. This is a true pheromonal effect and creates ovulation, right, and menstruation, or in rodents, it's an ester cycle, not a menstrual cycle. So this is not to say that the exact same things happen in humans. In humans, as I mentioned earlier, there's chemical sensing between individuals that may be independent of the nose, but those are basically the three paths by which smells, odors impact us. So I want to talk about the act of smelling. And if you are not somebody who's very interested in smell, but you are somebody who's interested in making your brain work better, learning faster, remembering more things, this next little segment is for you because it turns out that how you smell, meaning the act of smelling, not how good or bad you smell, but the act of smelling, sniffing and inhalation powerfully impacts how your brain functions and what you can learn and what you can't learn. Noam Sobel's group, originally at UC Berkeley and then at the Weizmann Institute, has published a number of papers that I'd like to discuss today. One of them, Human Non-Ole Factory Cognition, Phase Locked with Inhalation. This was published in Nature, Human Behavior, an excellent journal. As we inhale, what this paper shows is that the level of alertness goes up in the brain. And this makes sense because as the most primitive and primordial sense by which we interact with our environment and bring chemicals into our system and detect our environment, inhaling is a cue for the rest of the brain to essentially to pay attention to what's happening, not just to the odors. As the name of this paper suggests, human non-ole factory cognition, phase locked with inhalation. What that means is that the act of inhaling itself wakes up the brain. It's not about what you're perceiving or what you're smelling. And indeed, sniffing as an action, inhaling as an action, has a powerful effect on your ability to be alert, your ability to attend, to focus, and your ability to remember information. When we exhale, the brain goes through a subtle, but nonetheless significant dip in level of arousal and ability to learn. How should you use this knowledge? Well, you could imagine, and I think this would be beneficial for most people, to focus on nasal breathing while doing any kind of focused work that doesn't require that you speak or eat or ingest something. There is a separate paper published in the Journal of Neuroscience that showed that indeed, if subjects, human subjects, are restricted to breathing through their nose, they learn better than if they have the option of breathing through their mouth or a combination of their nose and mouth. Now, there are other ways to wake up your brain more as well. For instance, the use of smelling salts. I'm not recommending that you do this necessarily, but there are excellent peer-reviewed data showing that indeed, if you use smelling salts, which are mostly of the sort that include ammonia, ammonia is a very toxic scent, but it's toxic in a way that triggers this innate pathway, the pathway from the nose to the amygdala and wakes up the brain and body in a major way. This is why they use smelling salts when people pass out. They work because they trigger the fear and kind of overall arousal systems of the brain. This is why I think most people probably shouldn't use ammonia or smelling salts to try and wake up, but they really do work. Now, inhaling through your nose and doing nasal breathing, it's going to be a more subtle version of waking up your system, of alerting your brain overall. And for those of you that are interested in having a richer, a more deep connection to the things that you smell and taste, practicing or enhancing your sense of sniffing, your ability to sniff might sound like a kind of ridiculous protocol, but it's actually a kind of fun and cool experiment that you can do. You just do the simple experiment of taking, for instance, an orange, you smell it, do 10 or 15 inhales, followed by exhales, of course, or just through the nose. I'm not going to do all 10 or 15, and then smell it again. And you'll notice that your perception of that smell, the kind of richness of that smell will be significantly increased. So you can actually have a heightened experience of something. And that of course will also be true for the taste system. I'd like to take a quick break and thank one of our sponsors, Element. Element is an electrolyte drink that has everything you need and nothing you don't. That means the electrolytes, sodium, magnesium, and potassium in the correct ratios, but no sugar. We should all know that proper hydration is critical for optimal brain and body function. In fact, even a slight degree of dehydration can diminish your cognitive and physical performance to a considerable degree. It's also important that you're not just hydrated, but that you get adequate amounts of electrolytes in the right ratios. Drinking a packet of Element dissolved in water makes it very easy to ensure that you're getting adequate amounts of hydration and electrolytes. To make sure that I'm getting proper amounts of both, I dissolve one packet of Element in about 16 to 32 ounces of water when I wake up in the morning, and I drink that basically first thing in the morning. I'll also drink a packet of Element dissolved in water during any kind of physical exercise that I'm doing, especially on hot days when I'm sweating a lot and losing water and electrolytes. There are a bunch of different great tasting flavors of Element. I like the watermelon, I like the raspberry, I like the citrus. Basically, I like all of them. If you'd like to try Element, you can go to drinklmnt.com/huberman to claim an Element sample pack with the purchase of any Element drink mix. Again, that's Drink Element spelled LMNT. So it's drinklmnt.com/huberman to claim a free sample pack. You also can really train your sense of smell to get much, much better. No other system that I'm aware of in our body is as amenable to these kinds of behavioral training shifts and allow them to happen so quickly. In fact, how well we can smell and taste things is actually a very strong indication of our brain health. So our olfactory neurons, these neurons in our nose that detect odors are really unique among other brain neurons because they get replenished throughout life. They don't just regenerate, but they get replenished. So regeneration is when something is damaged and it regrows. These neurons are constantly turning over throughout our lifespan. They're constantly being replenished. They're dying off and they're being replaced by new ones.