Dispatches

Hub Dialogue: How your brain is structured to predict what’s going to happen next

In this Jan. 14, 2020 photo, research associate Jessica Trinh of the Allen Institute in Seattle handles a piece of live brain tissue. Ted S. Warren/AP Photo.

In this Hub Dialogue, The Hub’s editor-at-large Sean Speer speaks to Lisa Feldman Barrett, author of Seven and a Half lessons about the Brain.

This conversation has been revised and edited for length and clarity.

Sean Speer

I’m honored to be joined today by Lisa Feldman Barrett, who’s a neuroscientist, psychologist, and best-selling author at Northeastern University in Boston.

Professor Barrett’s work, which is focused on the intersection between human emotion and the brain, has earned her significant accolades, including most recently the American Psychological Association’s 2021 Distinguished Scientific Contributions award.

Today, we’re discussing her widely acclaimed book Seven and a Half lessons about the Brain, which contains seven short essays on different aspects of the brain, including, why we have one, how it works, and how it’s interconnected to brains around us.

Lastly, and perhaps most importantly, Professor Barrett was born in Toronto, completed her undergraduate degree at the University of Toronto and her PhD at the University of Waterloo which makes her another one of Canada’s great exports to the United States.

Thank you so much for joining us today, Lisa.

Lisa Feldman Barrett

It’s my pleasure to talk with you.

Sean Speer

Let’s start with the idea with which you open the book: The main purpose of the brain is not to think but to regulate our bodies. This may seem counterintuitive to some of our readers. How did you come to this conclusion? And why is it so important?

Lisa Feldman Barrett

Well, it’s counterintuitive to me as a person. I asked the question, “Why do we even have a brain?” Brains are really expensive metabolically. So, that three-pound blob of meat between your ears is about 20 percent of your metabolic budget. That’s the most expensive organ that you have. What’s it good for? Why did it evolve?

On the basis of evolutionary evidence, as well as the structure and architecture of the brain, what’s really clear is that the brain’s most important job is to regulate the systems of your body. You have many systems inside your body, all of which require oxygen, glucose, salt, potassium, and various other nutrients that are necessary to keep you alive and well.

You can think about your brain as running a budget for your body. It’s not budgeting money; it’s budgeting these nutrients, making sure that they get to where they need to be just before they’re needed. So, they’re available right when they’re needed.

I just found this to be really counterintuitive, because, of course, we don’t experience every feeling that we have, everything that we see, every hug that we give or every insult that we bear as having anything to do with our bodies. But your brain thinks, sees, feels and moves your body in the service of regulating the systems of your body.

So, you and I are talking right now, and if we were in the same room, our breathing would synchronize and our heart rates might synchronize. If you cross your leg, I might cross my ankles. If you scratched your arm, I might scratch my chin. Humans, when they like each other, and trust each other, tend to physically synchronize with each other. Even the words that we speak to each other have a huge impact on each other’s nervous systems. I can text three little words to a close friend who lives halfway around the world. She doesn’t have to see my face or hear my voice, and it will affect her breathing her metabolism and heart rate. For better. Or for worse.

Bodies are complex, with many systems that require coordination, and a command center is useful for accomplishing that coordination. As bodies evolved to become bigger and more complex over evolutionary time, brains evolved, and correspondingly they have also evolved to become bigger and more complex.

The structure of the brain makes it really clear that this is your brain’s most important job. And if you doubt that in any way, just think about what would happen if your brain wasn’t regulating your body all the time.

Why is it important? It’s important because many of the diseases that we think of in psychological terms actually have biological components related to the functioning of your body.

Take depression, for instance. We often think of depression is a mood disorder, but depression is also metabolic disorder – meaning that, fundamentally, there is something wrong with your metabolism and your energy regulation. When you experience depression, you don’t experience that metabolic difficulty directly; you experience it as fatigue or distress, and it’s those symptoms that send you to the doctor. But under the hood, there are real metabolic issues. Now, I’m not reducing depression to simply a metabolic problem. What I’m saying is that everything we experience psychologically and mentally has a biological component somewhere inside our brains.

Everything we experience is in our brain. You don’t see with your eyes, you see with your brain; you don’t smell with your nose, you smell with your brain. Sure, you can’t see without your eyes or smell without your olfactory bulb, but when you experience anything, it is being constructed in your brain.

You don’t smell, see, think and feel because it’s fun or interesting. In the wiring of the brain, it’s easy to see that your brain is doing these things because it’s helping to regulate your body. Understanding this allows us to break down the distinction between mental and physical disease. It helps us to figure out how to treat diseases and even maybe prevent them.

There’s a whole series of other more speculative questions that we can start asking that we would never have thought to ask before including, for instance, what it means when your body budget is running a deficit. It’s actually conceptually similar to what happens you’re running a deficit in your own budget.

What do you do when your actual budget runs a deficit? Well, at some point you stop spending. So, what does the brain do when its body budget is running a deficit? It’s also stops spending.

Now, what does it mean for a brain to stop spending? Well, it means that you don’t move around as much and you don’t learn new things. You stay “in your head” too much. Maybe you isolate yourself or surround yourself with people who are really predictable and like you. Maybe you don’t expose yourself to people who are different from you. Maybe you tend to avoid complexity and ambiguity, so you want simple single answers to complex issues and questions.

That, by the way, is the path to authoritarianism and totalitarian thinking. I’m not simplifying things to say, “look, if you’re metabolically compromised, you’re going to become like an authoritarian.” What I’m saying is that while we experience and understand things at the mental and social level, there’s this really basic metabolic level that we’ve been ignoring, and it’s important to understand as a piece of some of the biggest challenges that we face personally and also as a society.

Sean Speer

The book observes that most of the brain’s activities happen outside of our awareness. You even explain how the brain is constantly making predictions about what it expects to see – something you describe as “carefully controlled hallucinations.” How do our brains anticipate what’s going to happen or what will see next?

Lisa Feldman Barrett

As a person, if somebody told me, “You know, you’re not really reacting to stuff in the world, your brain is predicting everything,” I would be like, “What? How can you say that? That’s not my experience.”

But even as a really skeptical scientist, I experienced something really interesting when I was reading research in neuroanatomy. It suggested that the way a brain is structured is to predict what’s going to happen next. It’s not waiting to be stimulated by the world. It’s actually neurally-generating its own predictions, meaning it’s changing the firing of its own neurons, to anticipate sights, sounds, smells, and so on. At the same time, I was reading work in electrical engineering on signal processing, because the brain is a signal processor – there’s a lot of electrical drama going on in your neurons – and it suggested that the brain is predicting, not reacting. And I was reading other literatures that suggest prediction, too.

All these different literatures that don’t talk to or mention each other are pointing in the same direction, which is this really counterintuitive idea that brains are not structured and don’t function to react to things in the world, because that is metabolically inefficient. Instead, brains are structured to run an internal model of the world – to predict what to do next and what will be experienced next – and then adjust when that model is wrong.

Technically, I would say your brain is not running an “internal model of the world.” It’s actually running an “internal model of your body in the world.” So, your brain is receiving sense data through your eyes, ears, and nose, and it’s also receiving sense data from the internal conditions of your body – we call that the internal milieu of your body, from your heart beating, from your lungs expanding, and so on. And that sense data reaches your brain as the outcomes of some set of causes in the world and in your body.

Your brain doesn’t know the causes, it only knows the outcomes; it only receives information about the consequences. So, when you hear a loud bang, what is it? Did someone slam a door? Did someone drop a box? Did a car backfire? Was that a gun shot? The cause of the sound determines what you should do next. When you feel a tug in your chest, what was that? Is that the beginnings of a heart attack? Is that longing for a friend? Is that anxiety? Is that indigestion? Again, the cause of the tug is important for planning your next action.

But your brain doesn’t know the causes since it’s only receiving the outcomes. It doesn’t know the causes, so it has to guess, and it uses past experience to guess. So, your brain reassembles past experiences as potential guesses for what the causes are of these sense data that it receives. And it is guessing predictively. That’s what we mean when we say your brain runs an internal model. It’s basically making guesses. These guesses are not abstract ideas; they are literally your brain changing the firing of its own neurons, to anticipate sense data coming in, and it’s doing it predictively. That’s really a remarkable thing.

Here’s a cartoon description of what’s happening. If we were to stop time, and just take a look at inside your brain, what we would see is that your brain is modeling what it believes to be going on inside your body and outside in the world, and it’s associating, based on past experience, to make a guess, based on the statistics of your life, based on the last time you were in a similar situation. What did you do next? As a consequence, what did you see next? What did you feel next? What did you smell next? And so on.

A prediction is when your brain is changing the firing of its own neurons to prepare you to move your body in a particular way and to experience the world in a particular way, and this is unfolding before your brain makes itself aware of what’s going on. If you’ve ever had a song going through your head, your brain is changing the firing of your neurons so that you can hear a ghostly sound that is not there. Your brain uses exactly the same process to construct a prediction.

Your brain continually compares its predictions to the incoming input from your senses, and if the incoming input is a pretty good match, that input doesn’t make it very far into your brain because your neurons are already firing in a way to capture it. So, the sense data from the body and from the world are just there to confirm or correct what the brain’s internal dynamics are already doing. If your brain has failed to predict something, or has predicted something that does not materialize, we have a special name for this: we call it learning. Prediction errors are opportunities to learn, to adjust your brain’s internal model to present circumstances.

Sean Speer

To what extent does this predictive power create a past dependency? Are we slaves to our brain? Or do we still have free will?

Lisa Feldman Barrett

That’s such a great question. First of all, it’s so hard to talk about this without falling into Cartesian language. Are we slaves to our brain? Well, you are your brain; your brain is you. So, when I say your brain makes you aware, really, what I should say is, your brain makes itself aware, because you are not separate from your brain; your mind is a moment in your brain, so your mind is what your brain does, it’s what your brain creates as it regulates your body.

Do we have free will? I think we do, but maybe not in the way that is traditionally meant. For example, when your brain makes predictions, it doesn’t make a single ballistic prediction. It actually constructs a sample of predictions, each with its own likelihood of being correct. So, at best free will is probabilistic.

When your brain is constructing a group of predictions, it’s constructing concept or category. Your brain isn’t asking itself, “what are these sense data”, but rather “what are they similar to in my past experience?” A group of things that are similar to one another in some way is a category; a mental representation of a category is a concept. So your brain is engaging in category construction for the purposes of predicting the needs of your body and attempting to meet those needs before they arise, and as a consequence, it is also predicting what you will experience next. When a specific prediction is selected to account for the incoming sense data, this is the same as saying that the brain has categorized the sense data and made it meaningful. The brain categorizes what is new by comparing it to events and experiences that are similar in the past.

There are many aspects that contribute to selecting a specific prediction: the data from the outside world that are sensed with your retina, your cochlea and the other sensory surfaces of your body, the sense data from inside your body and your brain also has its own selection mechanisms, which is what we call “attention.” Attention also helps to bias, in a sense, or select which prediction is chosen which neural pattern is going to be completed and gain access to motor control, and which ones will be suppressed or will be allowed to peter out.

So, one source of free will or one source of choice is the automatic, probabilistic source – the stuff that you brain uses to choose one prediction signal over another. But there’s another source of free will, and that is, whenever you are faced with a situation where you can’t predict very well, you have an opportunity for learning, and learning changes what your brain is capable of predicting in the future, and therefore your actions and experiences that arise from those predictions.

If you cultivate new experiences for yourself, like traveling to place you’ve never been before or talking to somebody who’s different from you or seeing a movie or reading a new book, like Seven and a Half Lessons about the Brain, you’re exposing yourself to information that are new, and you’re cultivating new experiences for yourself. In effect, what you’re doing is you’re providing your brain with the opportunity to change its internal model, to rewire itself. And in effect learning influences how your brain will automatically predict in the future, and therefore how you will act in the future, what you will experience in the future… who you will be in the future.

In a sense, when you are cultivating new experiences for yourself in the moment, quite deliberately, often with effort, you’re forcing yourself to learn something new. You’re, in effect, continually cultivating your past … a past that will allow your brain to automatically predict differently in the future, and that is a kind of free will that we have.

So, if there’s a habit you want to break or a new habit you want to cultivate, or a behaviour that you want to change, or if you hold a value that you aren’t quite living up to, there are ways for you to change. It’s just that you have to invest in this change, and sometimes this takes much longer than you think it will, but in the end, it does work. I think this is a kind of free will that we often don’t talk about very much. But it’s very possible and a very real opportunity in our lives.

Sean Speer

Let me ask you about your broader research in the field of human emotions. What’s the relationship between emotions and the brain? Can we train ourselves to minimize our tendency towards emotion, and instead rely more on reason? Or is that question the wrong way to think about the interrelationship between emotion and the brain?

Lisa Feldman Barrett

Yeah, I think that’s the wrong way to think about it, and I would say there’s a lot of evidence to back me up on that.

As far back as ancient Greece, we’ve told a morality tale about what it means to be an ethical person. An idea that we have from Plato, for example, is that we have these inner instincts and passions, our inner wild beast, if you will, that must be tamed by our rationality. Instincts and passions are depicted as wild horses, and rationality is depicted as a charioteer trying to control two wild horses.

Throughout much of the 20th century, that idea was kind of tattooed onto the human brain. The idea was that a human brain has an inner beast: you have a lizard brain that is supposedly full of circuits for your instincts. And then you’ve got this wrapping around it called the “limbic system” – “limbic” literally meaning “border,” that supposedly contains your emotions, and that these are at home in the ancient parts of your brain that we share with other animals. Then we’ve got this big cerebral cortex, which is the supposed home of rationality, and the story is that your inner beast and your rational self are battling it out for control of your behaviour.

If your cerebral cortex wins, meaning rationality wins, then you’re moral and healthy. If your emotions or your instincts win, then either you’re immoral, because you didn’t try hard enough, or you’re sick, because you can’t control you know, your inner beast. That morality tale is embedded in Canadian law and in American law, in economic theory, in industry and medicine …. Its everywhere in our culture. But there’s one problem: it’s just not backed up by the anatomy, structure, or the functioning of the human brain.

Brains don’t work like a battleground. Your brain is always regulating your body, and your body is always sending sense data back to your brain. You don’t experience that sense data in high-dimensional detail the way that you see and hear in very high detail. We have really good vision, even those of us like me who wear glasses. We see things in a lot of detail, we hear things in a lot of detail, but we don’t feel every tug, every squirt, or every contraction in our bodies with the same detail. We’re not aware, for the most part, of the whole drama going on inside our own bodies. Or at least I hope you’re not aware; if you are, you have my tremendous sympathy, because there’s a lot of stuff going on inside your body right now, and if you are aware of it, then you’d find it impossible to pay attention to anything outside your own skin.

So your brain makes itself aware of the state of your body with simple feelings like feeling pleasant or unpleasant; comfortable or uncomfortable; worked up or calm. These simple feelings are like barometers for how your body budget is doing. These simple feelings are not emotions. They’re called an “affect” or “mood,” and they’re with you all the time, because your brain is always controlling your body, your body is always sending sense data back to your brain, even when you’re sleeping. So affective feelings are always with you, whether or not you are emotional, and whether or not you are aware of those feelings … whether they are in the background or whether they are front and center in your experience. You can think about these simple feelings as properties of consciousness, just like lightness and darkness in vision, loudness of sound and so on.

When your brain creates instances of emotion, it is using the same sort of prediction and correction that we talked about before. Your brain is always attempting to give meaning to incoming sense data from your body, in relation to what is going on around you in the world, by conjuring the past to predict the immediate future, which eventually becomes the present.

When your brain re-assembles past experiences of anger that you’ve learned and that have been wired into your brain as a child, your brain is constructing anger. When you are exposed to a culture and you encounter actions or meanings that are new to you, your brain still attempts to use past experiences … in effect, what you “know” about emotion … to try and give meaning of the sense data coming from your body in relation to what’s going on around you in the world around you. This is called “conceptual combination.” If this does not work, then there is a lot of prediction error – a lot of opportunity to learn new emotion knowledge, and this is called “emotion acculturation.”

A lot of times when people just say they want to be less emotional, I think what they really mean is they want to feel affect less intensely. They want to feel less unpleasant; they don’t want to feel fatigued; they don’t want to feel uncomfortable; they don’t want to feel distress; and they don’t want to suffer. They want to regulate their affect. That’s very hard to control. But remember that affect is linked to the state of your body budget, so controlling affect means taking better care of your body. And there are some things that we can do in this regard, that sound kind of mundane. Every time I say what I am about to say, I always preface it by saying that I’m about to sound like a nagging mother, but really, I am speaking to you as a neuroscientist, and what I am saying is backed up by a ton of scientific evidence: if you want to get control of your emotions, you need to sleep enough; you need to eat healthfully; you need to exercise; you need to take walks; you need to connect with people who you love and trust. There are lots of things that you can do to keep your body budget solvent. Because when you are running a deficit, that’s what it means to be stressed. And your brain is creating intense affect that will likely become an emotion.

“Stress” is an everyday word, but it is so misunderstood. Stress is when your brain prepares your body for a big metabolic outlay. Stress can be good, like when you exercise, or bad, like when you worry how other people evaluate you. Cortisol, which everyone calls a stress hormone, is not a stress hormone. It’s a hormone that gets glucose into your bloodstream quickly, because your brain predicts that you need it so that you can move your body or learn something new. So, right before you’re drag yourself out of bed in the morning, you have a cortisol surge. Right before you exercise, you have a cortisol surge. When you exercise for a certain amount of time, say about 20 minutes, you might start to feel unpleasant, and that’s because you’re depleting your body budget. You might feel better afterwards, because then you replenish your body budget. So, one way to manage your emotion is to manage your affect, to not feel so unpleasant, to not suffer. It’s not the only way, but it’s a good one.

The idea that you could ever have a moment of consciousness without an affect is unlikely, unless you have a non-neurotypical brain of some sort or you use pharmacological interventions.

Sean Speer

You noted at the outset that human brains are quite large. In fact, the book documents that they’re much larger than most mammals. Is there any relationship between the brain size and one’s intelligence? Are people with big brains necessarily smarter?

Lisa Feldman Barrett

This is a huge debate right now. Actually, it’s been a debate for a long time. First of all, I would say that the kinds of inferences that you can make when you compare brain size across different species do not generalize to the kinds of inferences that you can make about brain size when you compare individuals within a species.

Humans and other primates have fairly large brains for their body size. The average size of a human cerebral cortex is not bigger than what you would expect it to be for a primate who has a brain of our general size. However, when you look at the micro wiring of this very big cerebral cortex that we have, you can see that it is supped up in certain places relative to, say, a chimpanzee brain. Here is the cartoon version of a very complicated scientific story that is still changing because new things are being discovered all the time:

The information that you get from your eyes, ears and so on, all of that detailed information contains statistical regularities – there are patterns, with redundancies, and these redundancies are being removed, that is, the information from all your senses is being compressed into efficient little summaries as this information is passed to neurons at the front of the brain. This compression, or what you might refer to as a dimensionality reduction, is kind of like what happens with an mp3 or mp4, and how information and content are streamed over the internet.

All brains with a cerebral cortex are thought to compress information like this, but the bigger your brain is, the more room there is for more compression. What that compression gives a human brain is the ability to abstract, which means that we can take things which look different, smell different, taste different, and sound different, but treat them as similar in some functional way. Our brains create these compressed summaries and what these summaries represent are functions; they’re representing the function of something rather than what it looks like or sounds like or smells like.

So one thing that humans can do, really much better than other animals, even animals who’s have larger brains and much larger bodies, is abstraction. And that’s important. Because many of the great achievements of humanity, I would say, arise from this ability to abstract and to impose functions on things that are physically different from one another. We can create similarities that are based on things that can be used in a similar way, even if those things are physically different from one another. And we can impose the same function on very different things – so we create similarities that aren’t there in nature. This is something that I explained mostly in the last lesson in Seven and a Half Lessons about the Brain.

A simple example is money. We impose a function on little pieces of paper, and that is the ability to trade for material goods. The only reason why little pieces of paper have value as money is because we agree that they have value. This is an abstraction that we have created – we’ve imposed a function on something that it does not intrinsically have by virtue of its physical nature.

We’ve imposed this same function throughout human history on everything that has ever been used as currency: on salt; on barley; on gold; on diamonds; on big rocks in the ocean; even airspace above a building can be bought and sold as a commodity called “air rights.” These things – paper, salt, barley and so on – they exist in the physical world, but their function as “currency” exists only because we impose a function on them and we agree on that function; if we disagree, they lose their function. Even something like a promise of value in the future – a mortgage – is valuable and can be bought and sold only if we agree so. We have this amazing ability to do this because we have big brains that can do this compression, at least relative to other species.

The question you asked me is, is Person A, who has a bigger brain, more intelligent than Person B? That’s a huge debate, but I would say there’s probably not one thing that makes a person more intelligent than another person. Most psychological phenomena have complex causes. What I mean by that it is multiple, small influences work together to create something emergent or something bigger than the sum of its parts. And so, intelligence is probably more than just having a big brain.

Sean Speer

Well, Professor Barrett, the extent to which big brains are one of the variables behind high levels of intelligence, you obviously have a big brain.

Your book is Seven and a Half Lessons about the Brain and I’m sure readers at The Hub will find it as fascinating as I have found today’s conversation.

Thank you so much for joining us and sharing these extraordinary insights into your research. We’re very grateful to have had the time with you.

Lisa Feldman Barrett

It’s my pleasure. Thank you so much for inviting me to do this interview with you.

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