‘In the lectures Barrett gives to explain this model, she talks of the brain as a prisoner in a dark, silent box: the skull. The only information it gets about the outside world comes via changes in light (sight), air pressure (sound) exposure to chemicals (taste and smell), and so on. It doesn’t know the causes of these changes, and so it has to guess at them in order to decide what to do next.
How does it do that? It compares those changes to similar changes in the past, and makes predictions about the current causes based on experience. Imagine you are walking through a forest. A dappled pattern of light forms a wavy black shape in front of you. You’ve seen many thousands of images of snakes in the past, you know that snakes live in the forest. Your brain has already set in train an array of predictions.
The point is that this prediction-making is consciousness, which you can think of as a constant rolling process of guesses about the world being either confirmed or proved wrong by fresh sensory inputs. In the case of the dappled light, as you step forward you get information that confirms a competing prediction that it’s just a stick: the prediction of a snake was ultimately disproved, but not before it grew so strong that neurons in your visual cortex fired as though one was actually there, meaning that for a split second you “saw” it. So we are all creating our world from moment to moment. If you didn’t, your brain wouldn’t be able make the changes necessary for your survival quickly enough. If the prediction “snake” wasn’t already in train, then the shot of adrenaline you might need in order to jump out of its way would come too late.
The brain also receives information about heart rate, what the lungs are doing, the immune system, hormone levels and much more. “Interoception”, the constant monitoring of the state of the body, carries on largely below the level of conscious awareness. But it is absolutely crucial, because it determines affect – those feelings of pleasantness or unpleasantness, arousal or non-arousal that are always present, and which feed into our emotions.
The brain deals with inputs from the inside the same way it deals with ones from the outside – it makes predictions about what’s causing these changes based on what it has learned, assigning them meaning in the process. In How Emotions Are Made, Barrett tells the story of a date she reluctantly agreed to go on, which took an unexpected turn as her stomach flipped while she was having coffee with the guy. “OK, I realised, I was wrong,” she writes. “I must be attracted to him.” A few hours later she found herself in bed with … the flu. What had happened over coffee was that her brain had made a prediction of “infatuation” based on sensory information from her gut combined with her culture’s understanding of that emotion and how it is supposed to unfold.
The brain, Barrett argues, is constantly trying to balance a “body budget”, her translation of the “fancy scientific term” allostasis. An imbalanced body budget – too much stress on bodily systems, not enough opportunity for rest and repair – intrudes into consciousness as negative affect. That in turn might get interpreted as “coming down with something” or “feeling depressed”, depending on how bad it is, your past experiences and the cultural context.’ (from the Guardian)