This episode is also on Bilibili too.
In today’s episode, I want to introduce you to a new popular-science book in English, Seven and a Half Lessons About the Brain. I’ll talk about the book’s background in a moment. First, let’s begin with a small, deeply unsettling passage from the book.
Think back to a scene from everyday life. What scene? Drinking water.
Think about the last time you were thirsty and had a drink. You poured yourself a full glass and gulped it down. After the last sip, you put the glass down, and a few seconds later, you felt that your thirst had disappeared. Then, with the pleasant feeling of having your thirst relieved, you went off to do something else.
Pretty ordinary scene, right?
But do you know how long it takes for the water you just drank to be absorbed by your intestines and enter your bloodstream?
The answer is: 20 minutes!
In other words, your body does not actually replenish that water until 20 minutes later; your thirst is not truly relieved until then. But why do you already feel almost completely unthirsty within a few seconds of finishing your drink?
If the water has not even had time to be absorbed by your body in those few seconds, then what exactly is quenching your thirst?
I’ll keep the answer under wraps for now.
As I mentioned, this question comes from a new psychology book in English. Actually, it was published in 年月, so I suppose it is not exactly new anymore—new-ish, at best. Its title is Seven and a Half Lessons About the Brain, a popular neuroscience book that has attracted quite a bit of attention and praise overseas over the past half-year. I bought the English e-book on 上, so for now, please just take a look at the cover on screen. In this book, the author introduces the ½ most important scientific facts about the human brain, as she sees them.
The author of Seven and a Half Lessons About the Brain is Lisa Feldman Barrett (), a heavyweight psychologist and neuroscientist. Barrett is a Distinguished Professor in the Department of Psychology at Northeastern University, a Fellow of the American Academy of Arts and Sciences, and a Fellow of the Royal Society of Canada. Her main field of research is emotion. She is, without question, the heavyweight champion of the psychology of emotion today.
Seven and a Half Lessons About the Brain is her second book. Her first book already has a simplified-Chinese edition, and it sold pretty well. It is simply called How Emotions Are Made. You may have heard of it, or even read it. Anyone bold enough to give a book such a title is either delusional or a heavyweight.
But, unfortunately, being a heavyweight does not necessarily mean being good at writing books. Professor Barrett is one of those heavyweights who is not especially good at writing books. How Emotions Are Made is, frankly, a pretty lousy read. Its theoretical framework is actually incredibly powerful, and it presents a highly radical theory of emotion. In How Emotions Are Made, Professor Barrett practically body-slams ordinary people’s common sense about emotion, along with the emotion theories of many earlier psychologists.
But the book is poorly written—half of it keeps circling back to the same points over and over. Seven and a Half Lessons About the Brain is much better, but to be honest, its quality still falls short of Professor Barrett’s reputation.
To be honest, if Seven and a Half Lessons About the Brain were rated out of five stars, I could only give it three and a half. But what I hope to present today is an upgraded, enhanced edition of the book. After I finished reading it, I realized that the question of how drinking water can instantly relieve thirst actually leads to the book’s most valuable insight and connects some of its brightest ideas across different chapters. Taken out and discussed on their own, these ideas may actually make for a better experience than reading the whole book from beginning to end. So I am not going to walk through the entire book today. I will focus only on the part that shines brightest to me.
So I will not comment too much more. Let’s get to the point.
Let’s return to the answer to that opening question about water instantly relieving thirst: why does water absorption take 20 minutes, while thirst relief takes only 5 seconds? What is actually quenching your thirst the moment you finish drinking?
The answer is: the prediction made by your brain is what makes you feel no longer thirsty.
When you drink water, your brain combines sensations from your mouth, throat, and intestines to estimate how much you have drunk. It compares that amount with your current level of thirst, then makes a prediction—an assessment. When it decides that the water you drank will be enough to replenish your body with sufficient fluids 20 minutes from now, it cuts off the feeling of thirst 20 minutes early. It creates an illusion that makes you think your body has already replenished its fluids now. That way, you do not have to sit around suffering for 20 minutes; you can allocate that time to other tasks.
Put differently, your brain tricked you. You fell under the spell it cast. It sent your experience on a little time travel trip, letting you feel the future 20 minutes early.
That is why absorbing water takes 20 minutes, while quenching thirst takes only 5 seconds. Your brain changes your future prediction to change your current experience.
Of course, the idea that “the brain makes predictions” is nothing new. The brain is making predictions all the time. When you are crossing the street and see a car 100 meters away approaching rapidly, you will certainly stop and wait, because you predict that if you cross now, you will be hit a few seconds later. You are not stupid enough to say, “Huh? There is no car in front of me now, so I might as well cross.” Unless you are some old man who treats the road like his own courtyard, you are not going to “live in the present” like that. You will respond according to your prediction of the future.
So there is nothing special about the brain making predictions. What makes the “instant thirst relief” example a little unusual is that the brain not only predicts the future, but also drastically modifies the body’s physiological state and psychological state according to that prediction.
What is this like? It is like a factory predicting that a sales boom will arrive in a few months, and deciding to immediately adjust its budget: stop production that has nothing to do with that future boom, expand the production line for products that will sell well, and change the budget for raw materials, inventory, and logistics accordingly.
Exactly. I think the real keyword in the instant-thirst-relief example is not “making predictions,” but “making budgets.” If the brain predicts that the water you drink now will definitely be enough to replenish your body fluids in the future, then the body and mind do not need to keep spending energy and effort looking for water. They should save those limited resources and put them into other, more meaningful work. It is like a factory that has already produced a batch of goods: even if those goods are still with the logistics company and have not reached consumers, the factory does not need to keep staring at that batch. It should start producing the next one.
So, in the drinking-water example, the truly remarkable thing about the brain is that it acts like a company’s budgeting department. Based on its predictions about the future, it carefully draws up an accounting budget and makes the body and mind carry it out, so that our future payoff can be maximized as much as possible.
And this actually reflects a very profound question: what is the brain’s function, at the most fundamental level? What is the brain even for?
Your first reaction might be: obviously, the brain is for thinking. But that is not actually the case. Thinking is not the brain’s day job. The brain’s true day job, its most fundamental and essential function, is—making budgets.
I think this is Professor Barrett’s most important insight in Seven and a Half Lessons About the Brain: the brain’s essential function is not thinking, but budgeting for the body’s energy expenditure.
So what did Professor Barrett base this view on?
The evolutionary history of the brain and nervous system.
If we are going to talk about the evolutionary history of the brain and nervous system, we have to start a very, very long time ago.
A very, very long time ago, Earth was ruled by organisms without brains. One of them was the lancelet (amphioxus). Not the Wuchang fish you buy at a market today—we are talking about the lancelet. It is not even technically a fish, but a chordate that looks like a little stick.
The lancelet had already appeared in the oceans 550 million years ago. It lived an extremely simple life. Its nervous system was so basic that it could only control a few simple movements to swim through the sea. Its way of finding food was equally unsophisticated: it waited for opportunity. The lancelet would remain on the seafloor like a piece of seaweed and eat tiny organisms that happened to drift into its mouth. The lancelet did not care about flavor, because it had no sense of taste like ours; it had no eyes, only cells that could detect changes in light and darkness; and it could not hear sounds. Its nervous system was extremely primitive—just a small clump of nerve cells that did not yet qualify as a brain. The lancelet was, essentially, a stick that could digest food.
Then 50 million years passed, bringing us to 500 million years ago. While the lancelet was still waiting for food on the seafloor, Earth entered the Cambrian period and experienced what scientists now call the Cambrian explosion, with huge numbers of new species appearing. During this period, a very important biological behavior emerged: hunting. Certain organisms appeared that could finally sense the presence of another organism and even try to eat it. Before hunting emerged, animals did swallow one another, but mostly in the same wait-and-see manner as the lancelet. Once hunting appeared, “finding food” became more purposeful and more technically demanding. Hunting still did not require a brain at that point, but it took a major step toward the development of one.
The predators that appeared in the Cambrian turned Earth into a more competitive and dangerous place. Predators and prey entered an intense arms race. Both evolved the ability to sense the world around them, and both began developing more precise sensory systems. The lancelet could only distinguish light from dark, but these newly evolved organisms could really see things. The lancelet had only crude sensations through its skin, while these new organisms could feel their bodies in much greater detail. In some species, the skin even evolved the ability to detect subtle vibrations in the water and locate other objects. Sharks today still use this ability to locate prey.
As more powerful sensory abilities emerged, the key survival question for organisms became: “Hey, there is some blurry thing over there. Is it something I can eat, or is it going to eat me?”
So organisms that could sense their surroundings more accurately were more likely to survive and reproduce.
Who was responsible for sensing the environment? The nervous system, of course. The selection pressure created by having to sense the environment drove a quantum leap in the nervous system’s complexity.
At the same time, these predators and their prey both acquired another new ability: more precise movement. The lancelet’s sensory and motor nerves were intertwined, so it could perform only very basic movements—essentially just slide through the sea. But in this new world full of predators, both predators and prey began evolving more powerful motor systems. These new species could swim quickly, change direction, dive, deliberately move toward things that looked like food, and move away from things that looked threatening.
And the key to all of this was energy efficiency. If a predator moved slowly while chasing food, another predator that was better at mobilizing energy could snatch that food away with quicker movements. On the other hand, if prey animals were constantly jumping at shadows and wasting energy dodging everything they saw, they would have no energy left to escape when real danger arrived.
So living things had to save energy when it was time to save it, and spend energy when it was time to spend it. That was the only way to stay alive and do a decent job of it.
Doesn’t this sound a lot like a company? There are plenty of places where money needs to be spent, but the company’s finances are limited. What does it need most at that point? A competent budgeting department—someone to coordinate in advance when to spend and when to save, draw up a financial budget, and then spend according to its rules. That is how the company might actually grow in a healthy way.
What Cambrian animals were crying out for online was exactly this kind of budgeting department—one that could budget the body’s energy expenditure in advance.
So who took on this huge responsibility? Their nervous systems, of course. In a world where the strong eat the weak, the nervous systems of Cambrian animals became increasingly good at budgeting the body’s energy expenditure. They became increasingly good at predicting the situations they might face in the future and what kinds of energy demands their bodies would have in each one. Then they could make the necessary preparations and plans ahead of time.
So how did they predict their bodies’ future needs? The best reference material was past experience—in other words, memory. For example, when an animal approached a patch of seagrass where it remembered predators had often appeared in the past, it knew to draw on some of its bodily energy in advance and put itself on alert, so it could escape promptly if danger appeared.
The nervous system faced another challenge during this period. Animals’ bodies were evolving to become larger and more complex. They developed cardiovascular systems that could use the heart to deliver blood throughout the body, respiratory systems that could take in oxygen and breathe out carbon dioxide, and immune systems that could resist microbial infections.
These complex systems made budgeting extraordinarily challenging. When an animal’s design was simple, budgeting was basically like running a mom-and-pop shop where a couple discussed that evening how many pounds of flour to buy tomorrow. That was about the level of complexity. But once animals became this complicated, budgeting started to look more like managing a large publicly traded company. The difficulty of going from a mom-and-pop shop to a listed company is not even in the same league.
To keep such a complex body running properly, you have to precisely regulate water, blood, salt, oxygen, glucose, cortisol, sex hormones, and dozens of other resources. That workload was more than a simple nervous system could handle. They needed a command center—and that command center was the brain. The brain most likely evolved under this kind of selection pressure.
Today, our brains have to oversee the movement of every muscle, balance dozens of different hormones, regulate the energy supply for vast numbers of brain cells, digest food, expel waste, and fight disease. None of this stops throughout the six or seven decades of the average human lifespan. It’s an extremely busy command center, but also an extremely efficient and precise one.
At this point, we can answer the question I raised earlier: what exactly is the brain’s main job?
Now we know that the brain’s most important job is not thinking, rationality, emotion, imagination, creativity, or compassion. Its most important job is to create an energy budget for the body—food, shelter, emotional rewards, and so on—and in doing so complete the most important task nature has assigned you: stay alive, then pass your genes on to the next generation.
Of course, the brain thinks, feels, imagines, creates, and even tells you to hold your phone and listen to me ramble on here. But everything the brain creates—from memories to hallucinations, from ecstasy to shame—is part of its core task: creating an energy budget for the body.
In the past, many people compared the brain to a company, or to a military commander. But the brain is actually an accountant who does the budgeting. (Huh? That metaphor seems to have lost a lot of its presence all of a sudden.)
The metaphor may have less swagger, but this idea has quite a lot of explanatory power. Because if we use the idea that the brain is an accountant who does the budgeting to examine some psychological concepts we’ve long been familiar with, it can lead to some very fresh insights.
Take the concept of rationality, for example.
What does rationality mean?
According to the mainstream understanding, rationality means not being emotional. Rationality and emotion are opposites. Emotion means making decisions by following intuition and feelings, while rationality means calm thinking that is unemotional and doesn’t get led around by intuition.
But if we start from the idea that the brain’s core task is to create an energy budget, rationality should really be defined as a state in which you can make a reasonable budget under specific circumstances.
Whether something is rational or irrational isn’t about how calm you are. It’s about whether the brain is regulating your mental and physical state appropriately.
For example, when you’re on a battlefield, the brain guides the adrenal glands above your kidneys to secrete cortisol at full throttle. Cortisol is a hormone that enables energy to erupt quickly. At that point, the whole body goes into a tense, hypervigilant state, ready to respond immediately with all kinds of life-saving reactions at the slightest disturbance.
Would you call someone calm in that situation? Of course not! There’s absolutely no rationality in the conventional sense—they’re as emotional as it gets. But are their reactions appropriate? Extremely appropriate. The brain’s energy budget is doing a fantastic job. Without budgeting this way, the person could be shot dead at any moment. So this jumpy, not-at-all-calm person is actually being highly rational.
That’s how the idea that the brain is an accountant who does the budgeting offers a new take on the concept of rationality.
Between the traditional definition of rationality and this new one, I wonder which you prefer. Feel free to discuss it in the bullet comments and the comments section.
So those are the most valuable insights I personally took away after reading Professor Barrett’s Seven and a Half Lessons About the Brain: the brain’s essential function is not thinking, but budgeting for the body and mind.
This idea was actually put forward in that half lesson of the Seven and a Half Lessons About the Brain. In the book, it was treated merely as an appetizing opener, but I think it’s a real shame that Professor Barrett didn’t use it to tie the whole book together. In the later chapters, she only echoed the opening idea very superficially, and then spent most of the book forgetting about it entirely. Take the example of how drinking water seems to relieve thirst instantly: it comes from a fairly late chapter, and by the time she wrote that part, she may have forgotten that the example could echo the opening idea.
So today’s episode is what you get after I dug material out of different parts of the book and did some condensing of my own. If the simplified-Chinese edition ever comes out and you buy it, only to think, Huh? This doesn’t sound quite like what you told us. Don’t blame me—instead, come back and give me some credit.
Finally, here’s a promise for later. At the beginning, I mentioned that although Professor Barrett’s first book, How Emotions Are Made, is pretty weakly written, its core content is actually excellent. So if I get the chance and have the time, I’d also like to discuss How Emotions Are Made with you on this program.
You can also leave a comment telling me which psychology or neuroscience books you’d like me to talk about, or what kinds of knowledge you’d like to hear about.
If you enjoy my program, please follow, like, save, and comment. I’ll keep sharing new psychology knowledge on this channel. That’s all for today. See you next time.
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