Are you a professional pillow fighter or a 9-to-5 low-cost time travel agent? Or maybe real estate sales on Mars is your profession? It doesn't matter. Whatever it is you do, however complex or intricate, monday.com can help you organize, work a straight, and make it more efficient. monday.com is the one centralized platform for everything work related. And with monday.com, work is just easier. monday.com for whatever you run. Go to monday.com to learn more. Hello everyone, welcome to new books and psychology. I'm Bida Hamafar, your co-host. Today we're speaking with David Linden, a professor in the department of neuroscience at the Johns Hopkins University School of Medicine, about his book, The Compass of Pleasure. And now here's the interview. Today we're talking to David Linden, author of The Compass of Pleasure, how our brains make fatty foods, orgasms, exercise, marijuana, generosity, vodka, learning, and gambling feel so good. Thanks for being on new books in psychology, David. Thanks for having me. Can you start the interview off by telling us a little bit about how you came to write The Compass of Pleasure? Well, absolutely. I'm a professor of neuroscience at the Johns Hopkins University School of Medicine. And my own lab works on the biological basis of memory storage. But for the last two years, I've written books on neural function for a general audience. So I'm always looking for topics that I think people are very interested in, and pleasure, things like sex and food and drugs are certainly falling to that category. And where the story hasn't recently been told a lot, and where there has been exciting news research within the last 10 years. And the topic of the neural substrates of pleasure filled all three of those requirements. Okay, thanks. So do you think that people have to be familiar with neural anatomy before reading your book? Oh, not at all. The whole point of the book is that anyone can pick it up. So there is a little of neural anatomy in it, but I explain it for you. So this book doesn't require anybody who's graduated high school, I think, can read this book. That said, it's not spoon-fed either. When writing about science for a general audience, you always have to make a decision about how much technical material are you going to put in, and how much are you going to ask your reader to work? And in my case, I asked my reader to work a bit, because I think a lot of what's exciting about research and pleasure actually winds up in the details, and that requires learning a few factoids about neural anatomy and chemistry. Okay, now you refer to the pleasure circuit frequently in your book, and I was wondering if you could tell our audience what you'd like them to know about this. Right, so the central understanding that's come from this work in recent years is that we have a series of interconnected brain regions that become activated when you experience pleasure, and we call this the medial forebrain pleasure circuit, and medial just means it's in the middle of your brain and forebrain means that it's towards your front, the front of your brain, and these regions have names like the ventral tegmental area and the nucleus accumbens, and they are critically dependent upon the neurotransmitter called dopamine. So, for example, if you were really, really hungry, and we had you in a brain scanning machine, and we gave you a bite of food that you found particularly delicious, we would see neural activity in your medial forebrain pleasure circuit, or if you were, as people have done in labs, mostly in Holland, in a brain scanning machine with your another region sticking out into the room, and you were stimulated to orgasm while you were in the brain scanning machine, you would see these regions light up in that situation too, or if you take heroin, or if you smoke cigarettes, so all of these different pleasurable experiences have in common that they activate this medial forebrain pleasure circuit. Now, why is dopamine so important to the experience of pleasure? Well, that's a really good question. Dopamine is sort of the central messenger within the circuit, but to sort of reduce this to a question of qualia, why does dopamine release within the circuit feel pleasurable? The real answer is we don't know. We know that if you lose your dopamine, you have an inability to feel pleasure. So, for example, in the very latest stages of Parkinson's disease, which is a disease that kills off all the dopamine using neurons in the brain, you not only have the symptoms of Parkinson's disease that we have come to know about, that is to say a tremor at the onset of motion, but you also have people who become an hedonic. They become unable to feel pleasure, and as a consequence, they become very withdrawn, very uninterested in going out, exploring the world. Nothing seems any good. Okay. Now, can you tell the audience a little bit about how the pleasure circuit functions just naturally within their body? Well, as I mentioned earlier, the amazing thing is that a whole range of pleasurable experiences will cause dopamine release within this circuit. So, we talked about eating food when you're hungry, and I think it's important to talk a little bit about the details of that, because the amount of dopamine released actually tracks your subjective experience. So, if you're really hungry and you have the first bite of a food that's very delicious, well, that first bite tastes wonderful, right? And then as you eat and you eat and you become seated, maybe the last bite before you stop eating is okay, but it's not nearly as good as that first one. If we were to image dopamine release in your medial forebrain pleasure circuit, we would see a very large amount of dopamine released with a very first bite and a much smaller amount with a very last bite. Likewise, if we give you a food you love, big signal of dopamine release, if we give you a food that you're rather indifferent to a much smaller signal of dopamine release. But I think one thing that's crucial in understanding how the system works is that it's not just vices that activate this pleasure circuit, it's not just things like orgasm and food and drugs. It's also a number of virtuous behaviors like exercise and learning and meditation and giving to charities. That's interesting. I think our audience will certainly gravitate more towards the vices, but I can understand why the virtuous acts as well will activate that system. Now, one of your first chapters is on drugs and so I do have to ask you, in terms of the pleasure circuit, you do write that sometimes drugs will essentially hijack that circuit. Can you explain what you mean by that? Well, right, to explain what I mean by that, really we have to ask a question, what's the pleasure circuit for? And it turns out that the pleasure circuit is evolutionarily ancient. We share it with critters like frogs and lizards. We even share a very rudimentary form of the circuit with animals that don't have a proper brain at all, like roundworms that live in the soil. So what's the circuit for? Well, it's so that eating food and drinking water and having sex will be pleasurable so that you will be motivated to do them again and again and survive and have children and get your genes into the next generation. So it's rather straightforward evolutionarily. Remember, clever us, we have figured out how to activate the pleasure circuit artificially. So we didn't evolve to take a tobacco plant and dry it out and set it on fire in our mouths and inhale the fumes or to extract sap from the opium poppy and smoke it or inject it in our veins. Nonetheless, we have all these different drugs that can activate the pleasure circuit artificially, that can hijack it. So nicotine, alcohol, cannabis, cocaine, amphetamine, heroin, all of these drugs activate the pleasure circuit. And you might begin to think, oh, I get it all psychoactive drugs, activate the pleasure circuit because I just gave you a very long list. But that's not true. So for example, LSD does not activate the pleasure circuit. SSRI antidepressants don't activate the pleasure circuit. And as a consequence, SSRI antidepressants and LSD have no risk of addiction where any drug that does activate the pleasure circuit does confer some risk of addiction. And you might think, oh, okay, I get it, it activates a really a lot of dopamine release, then that's a high risk of addiction, and it activates just a little bit of dopamine release, that's a low risk. And that would be a very good guess, and it wouldn't be true. So if we look at the statistics, 4% of all people who ever try alcohol become alcohol addicts, and about 30% of all people who ever try heroin become heroin addicts, and about 80% of all people who smoke cigarettes become cigarette addicts. And in a way, this is deeply counterintuitive, because after all, the pleasure buzz that you get from a cigarette is much more subtle than the pleasure buzz that you get from heroin, which then begs the question, why are cigarettes so addictive? And the answer comes from the insight that the development of addiction is just a specialized form of learning, of associative learning. So let's imagine, by comparison, that you've got a dog, and you want to train your dog to come when called, and to train your dog, you've got a delicious steak that the dog loves, and you call come Rover, come Rover, and Rover comes, and then you give Rover the entire steak, but then your steak is gone for the day, and then maybe the next day you get a new steak, and you train Rover, come Rover, you give them the whole steak. Now eventually, Rover will learn to come when called, but it'll take a while. Now, if instead, you take that steak and you cut it into 200 little tiny pieces, and you go come Rover, Rover comes, give them a little morsel. A moment later, come Rover, Rover comes, give them a little morsel, and you repeat that until all your 200 pieces of steak are gone. Well, at that point, Rover has learned forever to come when called. When you take heroin, you get a big pleasure boost, like one big steak, but then you're unlikely to do heroin again for another 12 to 24 hours. However, when you smoke cigarettes, if you are a pack of a smoker and you puff about 10 times per cigarette, well, you're getting 200 little pleasure buzzes. You suck the cigarette, you get a little pleasure buzz, you suck the cigarette, you get a little pleasure buzz, just like the dog got rewarded 200 times. When you are smoking cigarettes, you're doing a very good job of training your inner dog, so to speak, and that's why cigarettes are so addictive. So you make it seem like there's a dosage and a frequency component to addiction, right? There absolutely is. All right, so now, moving from drug addiction to food addiction, which is another chapter of your book, why does overindulging ensue feel so good? Well, I think what we have to realize here is that evolution is slow and cultures and technologies change quickly by comparison. So, for most of our human evolutionary history, we lived in small hunter-gatherer groups and we had a diet that didn't have very many sweet things and didn't have very many fatty things. It didn't have very many things that were calorically dense, and where intermittent famine was often a risk. And so in that food landscape, if you encounter something sweet or something fatty, it makes a whole lot of sense to snark it all down and pack on some weight so that you might survive the next famine, whereas the person next to you might not. Of course, those ancient hardwired instincts that make fatty and sweet things so compelling for most of us don't serve us well when we live in the modern first world where we have essentially unlimited access to calories. Is there a difference in the type of calories that make certain foods seem more appealing than others? Well, there are, and we don't under, there's some things we know, but we don't entirely know why. So, for some reason, foods that we crave have certain qualities. Things with a crunchy fried exterior and a soft interior are often very craveable foods. Sweet things that have contrasting flavors and textures. So, for example, ice cream with like candy bits and nuts in it, for most people is much more craveable than a homogeneous ice cream that is just chocolate or just a blueberry, for example. We don't understand the neurobiology of what it is that makes those things more crave-inducing, but you don't have to understand the neuro biology if you are a test kitchen chef at TGI Fridays or the Frito-Lay Corporation and your goal is to encourage people to overeat massively. And that has been the goal of the food service industry. The average weight of someone in the United States has increased by 26 pounds between 1960 and today. And it's not because people's genes have changed. It's because the way food is marketed to people has changed. We tend to finish what's on our plate. So, if you do bigger servings, we eat it up. We tend to drink what's in our bottle of soda. So, if you make a giant bottle of soda, we tend to drink it up. We are well, we are drawn in by certain aromas of things that are sweet and fatty, of oils, cooking, and sweet smells like the cinnabon, perfume, blasted through airports and malls. And so, in order to create craveable foods, you don't actually need to understand the neurobiology. You just need to try things out. Absolutely. In your book, you write that food is more appealing sometimes when you're dieting or when you're stressed. Can you explain to the audience what you mean by that? Well, so, it turns out that your brain knows how much fat you have on your body. So, it essentially knows your body mass index and indicates how much fat you're carrying. So, how does your brain know this? Well, it turns out your fat cells secrete a hormone called leptin and leptin passes into your brain and it binds leptin receptors in a part of your brain called the hypothalamus. And it sets in motion a series of neural signals that control your appetite over the long term. So, these aren't the kinds of signals that tell you, "Oh, I'm hungry right now for a meal or my stomach is full on them and end a meal." They're the kinds of signals that control your overall appetite over many days to weeks. And what happens is that leptin suppresses appetite and increases metabolism. So, when you lose weight and your body fat goes down, you secrete left leptin, which means that your appetite goes up and your metabolism goes down. And when you gain weight and you add more fat mass, there's more leptin secreted, which means that your appetite goes down and your metabolism goes up. So, this is what we call a homeostatic system. It's kind of like the thermostat on the furnace or the air conditioner in your home. It tends to keep people within a particular weight range. Unfortunately, that weight range has been, is the weight range appropriate for a food landscape that most of us in the first world no longer live in, probably in obesity. And based on that explanation, I think I hope that our audience can better understand how difficult weight loss, particularly in the long term, really can be. Right, it is. So, it's all of us are capable of modest weight loss that we can keep off forever. And almost everyone is capable of dramatic weight loss that we can sustain briefly. But sustaining dramatic weight loss throughout your life is a really, really challenging thing to do. You're fighting against your body's homeostatic system, which is just making you hungry and slowing down your metabolism when you are below that set point. And this is kind of the nasty little biological secret that the multi-billion dollar a year diet industry doesn't want you to know. Certainly not. Moving on to your chapter on romantic love and sexual arousal. Are brain systems involved in both of those things the same? Well, they're not. And I mean, in truth, we know that just from our experience on the world, right? It's actually aroused feeling horny and feeling in love don't feel the same. So, there's got to be something different going on in the brain. And so, the question becomes, well, what does this look like if you have somebody in a brain scanner? So, if you have people in a brain scanner while they are watching porn, and these are people who enjoy porn, either men or women, and they are reporting that they are feeling sexually aroused. And you can actually put little probes on their genitals. There's like this sort of tampon shaped device that goes in a woman's vagina that can measure the degree of lubrication by shining a light beam on the walls of the vagina, or this kind of condom with a strain gauge arrangement that can go over a man's penis and measure his degree of erection. So, you can measure those things and say, oh, yeah, okay, these people say they're aroused and they are definitely aroused in their genitals, as well as in their brain. And then you image their brain, well, what's happening? So, when people are sexually aroused by watching porn, there is a modest activation of the brain's pleasure circuitry. It's not nearly as strong as you get when people actually have an orgasm, but it is noticeable. Now, let's contrast that with what happens when you have people who are newly madly deeply in love, and they've been recruited into the lab and told to bring along a photograph of their sweetheart's face. And they are gazing on their sweetheart's face, these newly madly deeply in love folks. What is the pattern of brain activation we see there? Well, we also see activation of the brain's pleasure surgery. So, in that way, it is similar to porn. But you also see a lot of other things. You actually see deactivation of brain regions that are involved in things like executive function, decision-making, social evaluation. And this completely swears with what we know about being in love. When we're newly madly deeply in love, we're not the best judge of our beloved character traits. We want to emphasize the good and diminish the bad. I might say, "Oh, well, that's sore on her lip. It will clear up soon." And that thing with the police, well, that was just a misunderstanding. And I'm sure she didn't mean it when she punched that child in the face. Because my brain systems are in a state to discount that information. But if you look at people watching porn, they don't have those reduction in those cognitive evaluative qualities. So, in that sense, feeling horny and feeling newly madly deeply in love overlap, but they are, nonetheless, distinct as well. Is there a point at which the frontal lobe activity in romantic love will actually increase instead of be deactivated? Not that anyone has seen so far. So, by increase, you mean increase over normal levels? No. What does happen, though, is if you do this experiment, instead of doing it in people who are newly madly deeply in love, you do it with people who've been in relationships, say, for 20 years or more. And then you have them look at the picture of their beloved. Well, in 19 out of 20 of those people, they say, "If you ask them, do you feel the same way about your beloved now as you did when you were first together?" 19 out of 20 people will say, "No, I don't. What I feel is good, it's warm, it's companionate, it's a more mellow form of love, but it's not that intense, fiery, passionate thing we had at first." But one out of 20 people will say, "Yeah, it's just the same as when we were first together, it's just as intense, just as passionate." And when I hear that, I think, "Oh, shit. Oh, shit. Oh, shit. Oh, shit." Much Oprah. They just want to appear a certain way. But astonishingly, when you get the 19 out of 20 in the brain scanner, very little pleasure circuit activation, very little, if any, deactivation of these reasoning and executive centers. But the folks, the one in 20 folks that report being still truly madly deeply after all those years, they actually do look in the brain scanner like the new lovers. And, well, so this raises a lot of questions. Are those folks born that way? Is it because they have particularly good relationships? If one person in a relationship has that, is the other person likely to also have it or not? And these are questions we don't know the answer to yet. Let's put gears a little bit now and talk about gambling. Why do some people who enjoy gambling go on to develop an addiction? Well, so we can ask this question about gambling, but it's actually the very same question for any kind of addiction. Why do some people who try alcohol become addicts? Why do some people, almost everyone has sex, and yet only a small fraction of people become true sex addicts? So, if we were, for example, to have a gambling addict and a heroin addict write the stories of their addiction. And then before we had the chance to read them, we hired someone to edit them and take it out the words that made specific reference to gambling or heroin. We had the two stories side by side. They'd be the exact same story, and they would go like this. Well, there was this thing I did, and it was really made me feel pleasure, so I did it some more, and that was great. And then as time went on, I needed to do it more often or more intensively or at a higher dose in order to get the same pleasure that I got with less frequent or lower dose consumption earlier. And that process is called tolerance. And then as time went on further, eventually what happened is that all of my liking got transformed into wanting. The pleasure drained away, and all that was left was the desire to avoid withdrawal symptoms, the desire to not have a panic attack, to fall asleep at night, to wake up in the morning, to function minimally in the world. And so when people develop addictions, it turns out that the neurons in the pleasure circuitry of the brain are physically, electrically, and chemically rewired by that experience. It changes the pleasure circuitry of the brain in a very dramatic fashion. Now, why do some people become addicts and others don't? Well, part of it is genetics. About 40% of the variation in most addictions can be determined by the genes you inherit from your mother and father. Now, there's no single addiction gene. There's a whole bunch of them, but not surprisingly, some of them have to do with the function of the neurotransmitter dopamine within the brain's pleasure circuit. So you might think, oh, I get it. If you've got, if you inherit gene variants that make it so that dopamine is super effective in your brain's pleasure circuit, then things will seem extra pleasurable to you, and then you'll be more likely to be an addict. And that turns out to be 180 degrees wrong. That's just the opposite. It turns out that if you inherit gene variants that make dopamine function less efficient, then you are more likely to be an addict. So I am fortunate not to have a predisposition for addiction. I can go to the tavern, have two whiskeys, feel a little tipsy, hang out with my friends, have a laugh, and go home. But my friend Ned, who inherited gene variants that make his dopamine system work less efficiently, in order to get the pleasure that I get with two whiskeys, he's got to have ten. And he more likely to become an addict as a consequence of that. So the genetics is about 40% of it. The rest of it has to do with one's life experience. And there are many things about life experience that are important, but we understand the best is stress. And you asked earlier about stress and eating, and I didn't answer, but we're finally getting to it now, because it's the same as eating and gambling and heroin. It turns out that stress is an explicitly biological phenomenon. So if you have an argument with your sweetheart, or if you're sacked from your job, or if you're fighting off the flu virus, all of those things are stressors. And they all cause your adrenal glands, which sit on top of your kidneys to create stress hormones. And those stress hormones pass into your bloodstream and into your brain. And they bind stress hormone receptors on neurons within your brain's pleasure circuit. And they set in motion a series of changes that ultimately make you crave. And that is why when you're stressed, you're more likely to eat, you're more likely to do drugs. If you're in recovery, you're more likely to relapse, or whether it's drugs, or alcohol, or gambling, or sex, or whatever it is. Thanks, David. Now, I know we've spent the majority of this morning discussing devices in your book, but you also do talk about the more virtuous behaviors, such as things like exercise. So can you explain to our audience what is happening in our brain when they experience something like a runner's high? Right. Well, that's a great question. And the first thing to say about runners high is that, of course, it's not specific to runners, right? Any form of intense aerobic exercise can produce it. The second thing is that it's actually fairly rare. In other words, feeling kind of mildly proud of yourself after a little run around the neighborhood isn't runners high. Runners high is a real euphoria. And actually, only about one in 10 people feel it regularly. If you go to the end of a marathon and ask people, are you feeling euphoric, nine out of 10 will say, no, I'm feeling just a little nauseated and exhausted. And one out of 10 will say, yeah, I'm feeling euphoric. And then if you look in those folks and you say, well, what's going on? Well, if you take their blood, as people did many, many years ago, 1970s, you saw that there was an increase in a chemical called beta endorphin. And endorphins are the brain's natural morphine-like molecules. And endorphins, when they act in the brain, can activate the brain's pleasure circuit. And we thought that might be the reason. Now, there's a problem with that, though. It turns out that beta endorphin doesn't cross the blood brain barrier. So beta endorphin the blood can't get to the brain, so it can't make you feel pleasurable. So that's not it. So there's two other possibilities. One of them is that your brain actually produces endorphins within the brain in the artificial cerebrospinal fluid, when you have intensive exercise and field runners high. And there's one study that indicates that might be the case. However, it's looking more and more likely that the relevant neurochemical culprit is not endorphins at all, but a different class of molecules called endocannabinoids. And you can probably guess from the sound of that what that is. This is your brain's natural marijuana-like molecules. And endocannabinoids, unlike beta endorphin, can rapidly transition between the bloodstream and the brain. And they go up in the bloodstream, they go up in the brain with exercise, and right now they're the best candidate for the chemical that is mediating runners high. But ultimately, through a series of electrical and chemical steps, endocannabinoids are producing this high through bio-affecting dopamine. Likewise, if you smoke cannabis, some of its effects are produced indirectly by increasing dopamine signaling within the pleasure circuit. Thanks, David. Now, wrapping up here a little bit, can you tell the audience what you think is kind of in store for the future study of pleasure circuit? Well, I think the most important thing to say within the next 15 years is that we will have, I think, an increased range of compounds that will blunt cravings. So right now, if you're a recovering addict and you want help controlling your cravings, there aren't that many things we can give you to try. For nicotine withdrawal, there is a drug called varenicline, but it has some cardiovascular side effects that are concerning. For alcohol and possibly also for some other drugs, there's a drug called naltrexone that is useful, but it's very, very early days. So I think we're going to see many more therapies that will help people in recovery stay clean, and manage their cravings when combined with therapy and stress reduction strategies like meditation, exercise, prayer, playing with your dog, all that good stuff. And what are you and your lab working on right now? Well, my lab doesn't work on pleasure. My lab works on other things like how memory is stored in the brain. So that's it. I'm a little bit of an outsider here, right? So I am a brain researcher, but actually my lab does very little work on this particular topic. I think you should think of me not as the super expert on pleasure, but rather the ambassador from the nation of neuroscience. So when I talk in my book, The Compass of Pleasure, I'm not putting forward the results from my own laboratory. I am evaluating and putting forward and explaining the results from many other researchers in the field. I think that's going to be good enough for our audience. David, on behalf of New Books and Psychology, I would just love to thank you for being on our show. Thanks for having me. It was fun. You've been listening to an interview with David Linden, author of The Compass of Pleasure. I'm Vida Humafar, co-host of New Books and Psychology. Thanks for listening.
What happens in our brains when we do things that feel good, such as drinking a glass of wine, exercising, or gambling? How and why do we become addicted to certain foods, chemicals and behaviors? David Linden, a neuroscientist at Johns Hopkins, explains these phenomena in his latest book, The Compass of Pleasure: How Our Brains Make Fatty Foods, Orgasm, Exercise, Marijuana, Generosity, Vodka, Learning, and Gambling Feel So Good (Viking, 2011).
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