Michelle: Mark, I’m going to throw a statistic at you. What do you think is the most addictive substance on the planet? Mark: Oh, that’s easy. It’s got to be something intense, right? Heroin? Maybe crack cocaine? Michelle: That’s what most people would say. But according to the research, it’s actually the one legally sold on nearly every street corner in the world. Nicotine. Mark: Get out of here. Cigarettes? More addictive than heroin? Michelle: In terms of the capture rate, yes. About 80% of people who try cigarettes become addicted. For injected heroin, it's closer to 35%. That staggering difference reveals the raw power of the brain's pleasure circuit, a system that runs our lives in ways we can barely comprehend. Mark: Wow. 80 percent. That’s not a habit, that’s a trap. Where is this coming from? Michelle: This is all from the brilliant book we're diving into today, The Compass of Pleasure: How Our Brains Make Fatty Foods, Orgasm, Exercise, Marijuana, Generosity, Vodka, Learning, and Gambling Feel So Good by David J. Linden. Mark: Right, and Linden is a top neuroscientist at Johns Hopkins. What’s fantastic about this book, and why it got such high praise when it came out, is that he’s not just some stuffy academic. He writes with this incredible wit, making this super complex brain science feel like a thrilling detective story. He’s a scientist who can actually tell a story. Michelle: Exactly. He starts the whole book with a hilarious story about being in a tuk-tuk in Bangkok, with the driver offering him a laundry list of vices. It perfectly sets the stage for this universal human struggle: we are creatures hell-bent on finding pleasure, while society is hell-bent on controlling it. And the story of how we even found the brain's pleasure center begins with a happy accident in a lab… involving some very, very confused rats. Mark: Confused rats? Okay, I'm hooked. What on earth are you talking about?

Michelle: Well, picture this: it’s 1953. Two researchers, James Olds and Peter Milner, are trying to study the part of the brain that controls sleep. They’ve got a rat in a box with a tiny electrode implanted in its brain. The plan is to give it a little zap to see if it makes the rat sleepy. Mark: Standard Tuesday in a neuroscience lab, I guess. Michelle: Except they missed. The electrode landed in a completely different spot by accident. So they put the rat in this big box, and every time it wanders into Corner A, they press the button. Zap. They expect the rat to avoid that corner, right? It's a mild shock, after all. Mark: Yeah, of course. It’s basic conditioning. Don't touch the hot stove. Michelle: The rat did the exact opposite. It went back to Corner A. Again and again. It wanted the zap. The researchers were baffled. They realized they could guide the rat anywhere in the box just by stimulating its brain. So they redesigned the experiment. They put a lever in the box that the rat could press itself to get the stimulation. Mark: Oh, I think I see where this is going. And it’s not good for the rat, is it? Michelle: Not at all. The rat started pressing the lever. And it didn't stop. It would press it up to seven thousand times an hour. It would ignore food, even when it was starving. It would ignore water. It would run across a painful electrified grid just to get to the lever. It would choose the lever over a mate. It would press that lever until it collapsed from sheer exhaustion. Mark: That is terrifying. So they accidentally discovered a real-life 'bliss button' in the brain? A switch so powerful it overrides every single survival instinct? Michelle: Precisely. They had stumbled upon what we now call the medial forebrain pleasure circuit. It’s this ancient, powerful pathway that’s designed to reward us for doing things that are good for survival—eating, drinking, having sex. But direct stimulation? That was a shortcut that the brain had no defense against. Mark: That’s just wild. But rats are one thing. Surely no one was crazy enough to try this on humans, right? Please tell me they didn't. Michelle: Oh, they did. And this is where the story takes a much darker, more ethically disturbing turn. In the 1950s and 60s, a psychiatrist at Tulane University named Dr. Robert Heath was doing experiments on his patients, many of whom were institutionalized and couldn't give proper consent. Mark: This already sounds horrible. Michelle: It gets worse. He had a patient, known only as B-19, who was a young gay man suffering from depression. In the deeply misguided view of the time, Heath decided he could "cure" his homosexuality. So he implanted electrodes directly into B-19's pleasure circuit. Mark: He was trying to use the bliss button to change someone's sexual orientation. That's monstrous. Michelle: It's deeply unsettling. And the results were dramatic. When B-19 was given a button to stimulate his own brain, he became obsessed. The book quotes the researchers, saying he experienced "an almost overwhelming euphoria and elation and had to be disconnected despite his vigorous protests." He would press it up to 1,500 times an hour. Mark: Just like the rat. He was trapped. Michelle: Exactly. Heath then tried to pair this intense pleasure with heterosexual stimuli, even hiring a prostitute. And while he claimed some temporary success, the experiment is now seen as a horrifying example of medical abuse. But what it proved, in the most chilling way possible, is that the human pleasure circuit is just as powerful and just as vulnerable as the rat's. We all have that button. Mark: And I guess the rest of the story is about how modern life has figured out a million ways to press that button without needing an electrode. Michelle: You've got it. These experiments, as disturbing as they are, gave us the map to the treasure chest. And what we've learned since is how easily that map can be hijacked. It's not just about zapping the brain directly; it's about what happens when we flood it with certain foods, drugs, or experiences.

Mark: Okay, so if we all have this pleasure circuit, why do some people get addicted and others don't? Is it just a matter of willpower? Michelle: That's the common misconception, and it's what Linden argues so powerfully against. He says addiction isn't a moral failing; it's a disease of the brain's learning and reward system. It's about the circuit getting physically rewired. A key idea here is the difference between "liking" something and "wanting" something. Mark: What do you mean? Aren't they the same thing? Michelle: Not to your brain. "Liking" is the actual pleasure you get from something—the taste of chocolate, the feeling of a drug. "Wanting" is the motivation, the craving for it. In a healthy brain, these are in balance. But with addiction, the "wanting" system goes into overdrive while the "liking" system actually gets weaker. Mark: Wait, so addicts want it more but enjoy it less? That sounds like a cruel joke. Michelle: It's the central paradox of addiction. Linden cites a quote from an addict: "It’s always good to know a little chemistry." And the chemistry here is that repeated, intense stimulation of the pleasure circuit causes the brain to adapt. It reduces the number of dopamine receptors to protect itself from the flood. This is called the "blunted dopamine hypothesis." Mark: So it’s like your brain is turning down the volume on pleasure? And you need more and more of the drug or behavior just to feel normal, let alone good? Michelle: That's a perfect analogy. You need to turn the volume up to 11 just to hear the music that everyone else hears at a 5. And this isn't just about drugs. There was a fascinating experiment with rats and food. Researchers gave one group of rats standard, healthy lab chow. They gave another group a "cafeteria diet." Mark: Let me guess. Tiny rat-sized bacon, sausage, and cheesecake? Michelle: You're not far off! It was a buffet of high-fat, high-sugar junk food. The rats on the cafeteria diet quickly became compulsive eaters. They'd keep eating even when they were getting painful foot shocks. And when the researchers looked at their brains, they saw the exact same thing as in drug-addicted rats: their dopamine receptors had been down-regulated. Their pleasure circuit was numb. Mark: So my inability to eat just one potato chip is basically a low-grade version of this? The food industry has engineered these foods to be so rewarding that they hijack the same pathways as cocaine? Michelle: That's Linden's argument. He says there's a "war going on for your ass," and that the food industry has become expert at creating hyper-palatable foods that maximally activate this circuit. And this rewiring is physical. He talks about a process called Long-Term Potentiation, or LTP. Mark: Okay, that sounds super technical. Break that down for me. Is it like the brain is carving a deeper groove for a habit? Michelle: That’s a great way to put it. LTP is the biological basis of learning and memory. When two neurons fire together, the connection between them gets stronger. It's like paving a dirt path into a superhighway. Addictive drugs and behaviors trigger this process in the pleasure circuit, creating a powerful, long-lasting "memory" of the reward. This is why cravings can be triggered by a sight, a sound, or a smell associated with the drug, years after someone has quit. Mark: It explains so much. Like the story of Bill Lee, the compulsive gambler in the book. His addiction wasn't about the money; it was about the chase, the anticipation. His brain was rewired for the gamble itself. Michelle: Exactly. He experienced the full cycle: tolerance, where he needed to bet more and more; withdrawal, where he felt physically ill without it; and relapse, often triggered by stress. His story is a heartbreaking illustration that a behavioral addiction can be just as biologically real and destructive as a substance addiction. Mark: Okay, so far this sounds pretty bleak. Our brains are these ancient machines, easily hijacked by modern vices. Is there any good news in this book at all?

Michelle: There is. And honestly, it's the most profound and hopeful part of the book. After laying out how this circuit can be hijacked for destructive ends, Linden reveals its true, broader purpose. He calls it the "neural unity of virtue and vice." Mark: The unity of virtue and vice? What does that even mean? Michelle: It means the exact same pleasure circuit—the one that gets rats to starve themselves, the one hijacked by heroin and junk food—is also activated by things we consider virtuous. Things like exercise, learning, and even generosity. Mark: Hold on. You're telling me that giving money to charity can feel like a drug to my brain? Michelle: In a way, yes! There was a brilliant study where people were put in a brain scanner. In some trials, they were forced to give money to a food bank, like a tax. In other trials, they could choose to donate voluntarily. And in both cases, the act of giving money away lit up the nucleus accumbens, a key hub of the pleasure circuit. Mark: So the "warm glow" of giving is a real, biological event? It feels good for the same reason a slice of cheesecake feels good? Michelle: That's what the evidence suggests. The brain doesn't seem to make a moral distinction. It just registers a salient, rewarding event. Pleasure is the compass it uses to tell us, "Hey, pay attention! This is important." And what's really mind-bending is that this can extend to completely abstract concepts. Mark: Like what? Michelle: Like the pleasure of just knowing something. They did an experiment with thirsty monkeys. The monkeys had to choose between two symbols on a screen. Choosing one symbol would lead to a reward, but a cue would tell them in advance if the reward would be big or small. Choosing the other symbol also led to a reward, but the cue was random and told them nothing. Mark: Okay, so one path gives them information, the other keeps them in the dark. The outcome is the same, they still get a drink. Michelle: Right. But the monkeys overwhelmingly preferred the informative path. They would essentially "pay" for the information by choosing it more often. And the brain scans showed that their dopamine neurons fired in response to the information itself. Just knowing what was coming was a reward. Mark: That's incredible. So our curiosity, our drive to learn and understand the world, is plugged into this same fundamental pleasure system. Michelle: It's our species' superpower. Linden argues that this ability to get pleasure from abstract ideas is what allows us to build civilizations, create art, and pursue long-term goals that go against our basic drives. A student can pull an all-nighter studying, forgoing sleep and comfort, because the idea of passing the exam has become a powerful, pleasurable motivator. Mark: So pleasure isn't the enemy. It's just the language the brain uses to tell us what it values. The trick is teaching it to value the right things. Michelle: That's the core message. Pleasure is our compass. The question is, where are we letting it point?

Michelle: When you pull it all together, the journey of this book is just fascinating. We start with this accidental, shocking discovery of a 'pleasure button' in the brain. Then we see how modern life, with its endless stream of hyper-palatable foods, drugs, and digital distractions, has become ruthlessly efficient at hijacking that button. Mark: Leaving us in that state of 'wanting more but liking it less.' It’s a recipe for misery. Michelle: It can be. But the final, crucial insight turns it all on its head. The system isn't just for base desires. It’s the same system that rewards us for solving a difficult problem, for connecting with another person, for an act of kindness. Pleasure isn't inherently good or bad; it's just a signal. It's the brain's bright, flashing neon sign that says, "This matters. Do more of this." Mark: So the real challenge of modern life isn't to deny pleasure, but to consciously calibrate that compass. To point it toward the things that build us up over the long term, not just the things that give us a quick, easy hit. Michelle: Exactly. It's about cultivating what Linden might call 'virtuous pleasures.' And recognizing that the satisfaction from mastering a skill or helping a friend is just as real, biologically, as any other kind. Mark: That's a much more empowering way to look at it. It makes you wonder, what are the 'virtuous pleasures' in your own life that you could lean into more? Maybe it's learning an instrument, or volunteering, or even just the satisfaction of a long run. Michelle: That’s a great question for everyone to think about. We'd love to hear your thoughts. What's a virtuous pleasure that you actively cultivate? Find us on our social channels and let us know. We love hearing from you. Mark: It’s a powerful reminder that we have more agency than we think. We can help train our own compass. Michelle: This is Aibrary, signing off.