The classical view of a quiet brain that is simply ‘reactive’ to input, and on being stimulated makes a response, is misguided. The brain’s billions of neurons are always stimulating each other, millions at a time. These huge cascades of stimulation, known as intrinsic brain activity, continue from birth until death. It’s like breathing, a process that requires no external catalyst...intrinsic brain activity is the origin of the dreams, daydreams, imagination, mind wandering, and reveries collectively called simulations in chapter 2. It also ultimately produces every sensation you experience, including your interoceptive sensations, which are the origins of your most basic pleasant, unpleasant, calm, and jittery feelings.
With past experiences as a guide, your brain makes predictions. Predictions not only anticipate sensory input from outside the skull but explain it…Your brain also uses prediction to initiate your body’s movements, like reaching your arm out to pick up an apple or dashing away from a snake. These predictions occur before you have any conscious awareness or intent about moving your body… Your brain issues motor predictions to move your body well before you become aware of your intent to move.
Right now, as you read these words and understand what they mean, each word barely perturbs your massive intrinsic activity, like a small stone skipping on a rolling ocean wave...You might think that your perceptions of the world are driven by events in the world, but really they are anchored in your predictions, which are then tested against those little skipping stones of incoming sensory input.
In a sense, your brain is wired for delusion: through continual prediction, you experience a world of your own creation that is held in check by the sensory world. Once your predictions are correct enough, they not only create your perception and action but also explain the meaning of your sensations.
Simple pleasant and unpleasant feelings come from ‘interoception’ - an ongoing internal process that is your brain’s representation of all sensations from internal organs and tissues, hormones in the blood, and the immune system. Interoception is one of the core ingredients of emotion, but feelings coming from interoception are much simpler than full-blown emotional experiences like joy and sadness.
From your brain’s point of view, locked inside the skull, your body is just another part of the world that it must explain. Your pumping heart, your expanding lungs, and your changing temperature and metabolism send sensory input to your brain that is noisy and ambiguous. A single interoceptive cue, such as a dull ache in your abdomen, could mean a stomachache, hunger, tension, an overly tight belt, or a hundred other causes. Your brain must explain bodily sensations to make them meaningful, and its major tool for doing so is prediction. So, your brain models the world from the perspective of someone with your body. Just as your brain predicts the sights, smells, sounds, touches, and tastes from the world in relation to the movements of your head and limbs, it also predicts the sensory consequences of movements inside your body.
My lab has discovered that these regions form an interoceptive network that is intrinsic in your brain, analogous to your networks for vision, hearing, and other senses. The interoceptive network issues predictions about your body, tests the resulting simulations against sensory input from your body, and updates your brain’s model of your body in the world. To simplify our discussion drastically, I’ll describe this network as having two general parts with distinct roles. One part is a set of brain regions that send predictions to the body to control its internal environment: speed up the heart, slow down breathing, release more cortisol, metabolize more glucose, and so on. We’ll call them your body-budgeting regions. The second part is a region that represents sensations inside your body, called your primary interoceptive cortex.
Your body-budgeting regions make predictions to estimate the resources to keep you alive and flourishing, using past experience as a guide. Why is this relevant to emotion? Because every brain region that’s claimed to be a home of emotion in humans is a body-budgeting region within the interoceptive network. These regions, however, don’t react in emotion. They don’t react at all. They predict, intrinsically, to regulate your body budget. They issue predictions for sights, sounds, thoughts, memories, imagination, and, yes, emotions. The idea of an emotional brain region is an illusion caused by the outdated belief in a reactive brain. Neuroscientists understand this today, but the message hasn’t trickled down to many psychologists, psychiatrists, sociologists, economists, and others who study emotion.
Affect, which depends on interoception, is the general sense of feeling that you experience throughout each day. It is not emotion but a much simpler feeling with two features. The first is how pleasant or unpleasant you feel, which scientists call valence…The second feature of affect is how calm or agitated you feel, which is called arousal.
When you experience affect without knowing the cause, you are more likely to treat affect as information about the world, rather than your experience of the world. Experiencing supposed facts about the world that are created in part by our feelings is called affective realism. For example, people report more happiness and life satisfaction on sunny days, but only when they are not explicitly asked about the weather.
Take a moment and consider what this means for your day-to-day life. You’ve just learned that the sensations you feel from your body don’t always reflect the actual state of your body. That’s because familiar sensations like your heart beating in your chest, your lungs filling with air, and, most of all, the general pleasant, unpleasant, aroused, and quiescent sensations of affect are not really coming from inside your body. They are driven by simulations in your interoceptive network… In short, you feel what your brain believes. Affect primarily comes from prediction.
...you see what your brain believes—that’s affective realism. The same is true for most feelings you’ve experienced in your life. Even the feeling of the pulse in your wrist is a simulation, constructed in sensory regions of your brain and corrected by sensory input (your actual pulse). Everything you feel is based on prediction from your knowledge and past experience. You are truly an architect of your experience. Believing is feeling.
Let me show you what this means. You might think that in everyday life, the things you see and hear influence what you feel, but it’s mostly the other way around: that what you feel alters your sight and hearing. Interoception in the moment is more influential to perception, and how you act, than the outside world is.
You might believe that you are a rational creature, weighing the pros and cons before deciding how to act, but the structure of your cortex makes this an implausible fiction. Your brain is wired to listen to your body budget. Affect is in the driver’s seat and rationality is a passenger. It doesn’t matter whether you’re choosing between two snacks, two job offers, two investments, or two heart surgeons—your everyday decisions are driven by a loudmouthed, mostly deaf scientist who views the world through affect-colored glasses.
The human brain is anatomically structured so that no decision or action can be free of interoception and affect, no matter what fiction people tell themselves about how rational they are. Your bodily feeling right now will project forward to influence what you will feel and do in the future. It is an elegantly orchestrated, self-fulfilling prophecy, embodied within the architecture of your brain.
If the idea of the rational human mind is so toxic to the economy, and it’s not backed up by neuroscience, why does it persist? Because we humans have long believed that rationality makes us special in the animal kingdom. This origin myth reflects one of the most cherished narratives in Western thought, that the human mind is a battlefield where cognition and emotion struggle for control of behavior. Even the adjective we use to describe ourselves as insensitive or stupid in the heat of the moment—“thoughtless”—connotes a lack of cognitive control, of failing to channel our inner Mr. Spock. This origin myth is so strongly held that scientists even created a model of the brain based on it. The model begins with ancient subcortical circuits for basic survival, which we allegedly inherited from reptiles. Sitting atop those circuits is an alleged emotion system, known as the “limbic system,” that we supposedly inherited from early mammals. And wrapped around the so-called limbic system, like icing on an already-baked cake, is our allegedly rational and uniquely human cortex. This illusory arrangement of layers, which is sometimes called the “triune brain,” remains one of the most successful misconceptions in human biology.
The bottom line is this: the human brain is anatomically structured so that no decision or action can be free of interoception and affect, no matter what fiction people tell themselves about how rational they are. Your bodily feeling right now will project forward to influence what you will feel and do in the future. It is an elegantly orchestrated, self-fulfilling prophecy, embodied within the architecture of your brain.
Your interceptive predictions, which produce your feelings of affect, determine what you care about in the moment—your affective niche. From the perspective of your brain, anything in your affective niche could potentially influence your body budget, and nothing else in the universe matters. That means, in effect, that you construct the environment in which you live. You might think about your environment as existing in the outside world, separate from yourself, but that’s a myth. You (and other creatures) do not simply find yourself in an environment and either adapt or die. You construct your environment—your reality—by virtue of what sensory input from the physical environment your brain selects; it admits some as information and ignores some as noise. And this selection is intimately linked to interoception. Your brain expands its predictive repertoire to include anything that might impact your body budget, in order to meet your body’s metabolic demands. This is why affect is a property of consciousness.
Interoception, as a fundamental part of the predictive process, is a key ingredient of emotion. However, interoception alone cannot explain emotion. An emotion category like anger or sadness is far more complex than a simple feeling of unpleasantness and arousal.
Affect alone also doesn’t explain how we construct our own experiences of sadness, nor how one instance of sadness differs from another. Nor does affect tell you what sensations mean or what to do about them. That’s why people eat when they are tired or find a defendant guilty when they are hungry. You must make the affect meaningful so your brain can execute a more specific action. One way to make meaning is to construct an instance of emotion.
So, how do interoceptive sensations become emotions? And why do we experience these sensations (really predictions) in such diverse ways: as physical symptoms, as perceptions of the world, as simple affective feeling, and sometimes as emotion? That is the subject of the next chapter, chapter 5, “Concepts, Goals, and Words”