Michelle: Your brain uses about 20% of your body's total energy, more than any other single organ. It's an incredibly expensive piece of biological machinery. Mark: Right, and I assume that’s for all the brilliant, complicated thinking I’m doing. Or, more realistically, for worrying about whether I left the stove on. Michelle: That’s what we all assume. But what if most of that energy isn't spent on thinking at all? What if it's spent on running a budget? A biological budget that determines literally everything you feel and do, from getting out of bed to falling in love. Mark: A budget? My brain is an accountant? I thought my brain was for having big ideas and composing witty emails, not for crunching numbers on my glucose levels. That’s… a little disappointing, honestly. Michelle: It sounds it, but it's actually the most profound and powerful idea in modern neuroscience. And it’s the core of the book we're diving into today: Seven and a Half Lessons About the Brain by Lisa Feldman Barrett. Mark: Ah, Lisa Feldman Barrett. I've heard her name. Isn't she a pretty big deal in the science world? Michelle: A huge deal. She’s one of the most-cited scientists on the planet, and she's famous for taking a sledgehammer to popular but deeply wrong ideas about the brain. This book is her short, sharp, and sometimes shocking guide to what's really going on inside our heads. And her first lesson is the biggest myth-bust of all.

Michelle: She states it plainly: your brain is not for thinking. Mark: Okay, hold on. That feels like saying lungs aren't for breathing. What have I been doing with it my whole life, then? Using it as a paperweight? Michelle: You've been using it for its primary, most ancient job: managing your body's resources. Barrett calls it "body budgeting." The technical term is allostasis. Your brain’s number one priority, honed over 500 million years of evolution, is to keep your body alive and well by making smart investments with your energy. Mark: So it’s like a financial advisor for my body? Deciding whether I have enough energy capital to spend on, say, arguing with a stranger on the internet? Michelle: Precisely. Every single thing you do is a withdrawal from that budget. Getting coffee, learning a new skill, even just scrolling on your phone. And things like sleep, good food, and a walk in nature are deposits. Your brain is constantly predicting what withdrawals you'll need to make and trying to balance the books. Mark: Where does this idea even come from? It completely upends how I picture my own brain. Michelle: It comes from looking at the deep history of life. For a long time, creatures didn't have brains. Think of the amphioxus, a little worm-like creature that still exists today. It’s basically a stomach on a stick. It has no brain. It just floats around, and if food drifts into its mouth, it eats. If something bumps into it, it moves. It only reacts. It doesn't need a brain because its life is simple. Mark: It sounds blissful, actually. No meetings, no deadlines. Michelle: But then, about 500 million years ago, something changed. The Cambrian Explosion. And with it came one of the most disruptive innovations in the history of life: hunting. For the first time, creatures were actively trying to eat other creatures. The world suddenly became a very dangerous, competitive place. Mark: And just reacting wasn't good enough anymore. If you wait until a predator's teeth are in you to react, you've already lost. Michelle: Exactly. Survival now depended on something new. It depended on prediction. An animal that could predict where a predator might be, or where food might be found, had a massive advantage. But prediction is metabolically expensive. You need a central command center to gather all the data from the senses, compare it to past experiences, and make a guess about the future. And that command center is the brain. Mark: So the brain didn't evolve to ponder the meaning of life. It evolved to guess whether that shadow over there is a rock or a thing that's about to eat me, and to manage the energy needed to either run or relax. Michelle: That’s the entire game. The brain’s job is to run that little worm body that has become incredibly complicated. All the amazing things the human brain can do—compose symphonies, discover quantum physics, create art—are, in Barrett's view, magnificent side effects of a master budgeter getting really, really good at its job over millions of years. Thinking is a great way to make deposits into your body budget, by finding food, shelter, and a mate. But it's not the reason the brain exists. Mark: That is a wild reframing. It makes me feel both less special and more amazing at the same time. My brain isn't some ethereal thinking machine; it's this gritty, survival-obsessed organ. But the way it achieves that survival is by creating these incredible mental worlds. Michelle: And the way it creates those mental worlds is the next lesson, and it's even more mind-bending. The brain manages its budget so efficiently because it doesn't just wait for information to come in from the outside world. It actively guesses what's about to happen.

Mark: What do you mean it guesses? Like, it has a little crystal ball in there? Michelle: In a way, yes. The crystal ball is all your past experiences. Barrett argues that your brain is a predictive organ, not a reactive one. From the moment you're born, it's building a model of the world. And it uses that model to constantly predict what sensory information is about to come in. Your reality is basically a controlled hallucination. Mark: A controlled hallucination? That sounds… unstable. You’re saying what I’m seeing and hearing right now isn’t real? Michelle: It’s real to you because your brain says it is. But it’s not a perfect photograph of the outside world. It’s a construction. Your brain receives noisy, ambiguous data from your eyes, ears, and other senses. It then asks itself, "What in my past is this most like?" and generates a prediction. The sensory data just confirms or corrects the prediction. Most of the time, what you experience is your brain's prediction, not the raw data itself. Mark: I need an example. A really strong one. Because that is a huge claim. Michelle: Barrett provides a powerful and unsettling one. It's the story of a man who served in the Rhodesian army. He was on patrol in the forest, on high alert. He saw movement ahead and his brain, primed by his training and the constant danger, instantly predicted a line of enemy guerrilla fighters. He saw them, clear as day. He raised his rifle, aimed at the leader, and was about to fire. Mark: Oh man, I can feel my heart rate going up just hearing this. Michelle: Right as he was about to pull the trigger, his buddy grabbed his arm and whispered, "Don't shoot. It's just a boy." The soldier lowered his rifle and looked again. And this time, his brain constructed a different reality. He saw a young shepherd boy leading a herd of cows. The "machine gun" he saw was just a herding staff. Mark: Whoa. So his brain literally created enemies that weren't there. It wasn't that he was mistaken, or his eyes were playing tricks on him. He saw them. Michelle: He saw them. Because his brain's prediction was so strong, driven by the high-stakes context of war, that it overrode the ambiguous sensory data. His brain wasn't wired for accuracy in that moment; as Barrett says, it was wired for survival. It's better to mistakenly see a threat that isn't there than to miss a threat that is. Mark: That's terrifying. Does this happen to us in less extreme situations? Like, on a normal Tuesday when I'm not in a warzone? Michelle: All the time, just in lower-stakes ways. It's why you might misinterpret a short email from your boss as angry—your brain predicts a negative tone based on past anxieties. It's why you can read a sentence with jumbled letters as long as the first and last letters are correct. Your brain predicts the word and fills in the blanks. Your experience of the world is a constant collaboration between sensory data and your brain's predictions. Mark: This has huge implications for things like eyewitness testimony in court. Or even just arguments between couples. We're both experiencing our own brain's "controlled hallucination" of what happened. Michelle: Absolutely. And it raises an even bigger question. If my brain is automatically initiating my actions based on past data and predictions, how much control do I really have? What does that say about free will? Mark: Yeah, that’s the elephant in the room. Am I just a puppet of my past experiences? Michelle: Barrett's answer is both humbling and empowering. You can't change your past, but you can change your future predictions. By learning new things, having new experiences, and deliberately exposing yourself to different perspectives, you are curating the data your brain will use for its future predictions. You are, in a very real sense, sculpting your future self.

Michelle: And that question of control and sculpting our brains is where her final lesson hits the hardest. Because our predictive brains don't operate in a vacuum. We are constantly, and mostly unconsciously, regulating each other's body budgets. Mark: What does that even mean? How can I regulate your body budget? Michelle: Through words, gestures, and even just your presence. As social animals, we are each other's environment. Barrett has this incredible line: "The best thing for your nervous system is another human. The worst thing for your nervous system is also another human." We are constantly making deposits and withdrawals in each other's body budgets. A kind word is a deposit. A cruel remark is a withdrawal. Mark: So when someone is chronically stressed by a toxic boss or a bad relationship, it's not just "in their head." It's a sustained biological assault on their body budget. Michelle: It's a biological assault. And this is not a metaphor. Chronic stress from verbal aggression or social rejection floods the body with hormones like cortisol, which over time can damage brain tissue, weaken the immune system, and lead to illness. We are that deeply connected. Mark: That makes me think about the responsibility we have. Every interaction matters. Michelle: It matters in a way we can barely comprehend. And the most tragic and powerful illustration of this is the story of the Romanian orphans. In the 1960s, the dictator Nicolae Ceaușescu outlawed contraception and abortion to boost the population. It led to hundreds of thousands of children being abandoned in state-run orphanages. Mark: I’ve heard about this. The conditions were horrific, right? Michelle: Beyond horrific. In many of these places, babies were warehoused in rows of cribs. They were fed and changed, but they were never held, never spoken to, never played with. They were deprived of the most fundamental human social input. They were, in essence, removed from the human social world. Mark: My god. What happened to them? Michelle: The results were devastating. These children grew up with stunted bodies and smaller-than-average brains. They had profound intellectual and emotional difficulties. Their brains, which are born expecting a rich world of social input to guide their wiring, received almost none. The "tuning and pruning" process that shapes a healthy brain went terribly wrong. Without that social regulation from caregivers, their brains simply couldn't develop properly. Mark: That's just heartbreaking. It makes the phrase "words can hurt" feel like a massive understatement. It's more like, "a lack of loving words can prevent a brain from even forming correctly." Michelle: Exactly. It proves that we have the kind of nature that absolutely requires nurture. Our brains are not pre-programmed. They arrive "under construction" and expect other brains to help them finish the job. We are all, in a very real sense, co-creators of each other's minds. Mark: This changes everything about how I think about community and society. Every toxic comment section, every political shouting match, every act of social isolation… it’s not just bad manners. It’s a public health issue. We are literally draining the biological resources of the people around us. Michelle: We are. And we're also responsible for making deposits. That's the flip side. Empathy, kindness, cooperation, and basic human dignity aren't just nice ideas. They are essential tools for our collective survival and well-being. They are biological necessities.

Michelle: So when you put it all together, you get this incredible new picture of the human brain. We start with a brain that's not for thinking, but for budgeting our body's energy. Mark: Right, and it does this by constantly predicting the world, not reacting to it. Which means our experience of reality is a kind of controlled hallucination, built from our past. Michelle: And finally, that predictive brain isn't a solo act. It's part of a vast, interconnected network of other brains. We are constantly wiring and regulating one another, for better or for worse. Mark: It feels like the big takeaway is a profound sense of responsibility. Not just for our own actions, but for how we are actively participating in the biological regulation of everyone around us. We are all managers of this shared human ecosystem. Michelle: That's a perfect way to put it. And Barrett offers a very practical, hopeful path forward. She says we have more control than we think, because we can change our future predictions. One of the most powerful things we can do is simply try to understand why someone believes what they do, even, and especially, if we disagree with them. Mark: How does that help? Michelle: Because it feeds your brain new data. It seeds your brain to predict differently in the future. It makes the "other" less of a threat and more of a complex person. It's a small act, but it's an act of rewiring your own brain toward empathy. It's a deposit not just in their body budget, but in your own. Mark: That’s a really powerful idea. It’s not about agreeing, it’s about expanding your brain’s model of the world. So, a final question for our listeners to ponder, inspired by the book: What's one small thing you could do this week to make a deposit in someone else's body budget? Michelle: A beautiful question to end on. It could be a simple thank you, a moment of patient listening, or sharing something you learned today. Mark: This is Aibrary, signing off.