Incognito: The Secret Lives of the Brain

by David Eagleman

Brains are in the business of gathering information and steering behavior appropriately. It doesn’t matter whether consciousness is involved in the decision making. And most of the time, it’s not. Whether we’re talking about dilated eyes, jealousy, attraction, the love of fatty foods, or the great idea you had last week, consciousness is the smallest player in the operations of the brain. Our brains run mostly on autopilot, and the conscious mind has little access to the giant and mysterious factory that runs below it.

And who can blame you for thinking you deserve the credit? The brain works its machinations in secret, conjuring ideas like tremendous magic. It does not allow its colossal operating system to be probed by conscious cognition. The brain runs its show incognito. So who, exactly, deserves the acclaim for a great idea? In 1862, the Scottish mathematician James Clerk Maxwell developed a set of fundamental equations that unified electricity and magnetism. On his deathbed, he coughed up a strange sort of confession, declaring that “something within him” discovered the famous equations, not he. He admitted he had no idea how ideas actually came to him—they simply came to him. William Blake related a similar experience, reporting of his long narrative poem Milton: “I have written this poem from immediate dictation twelve or sometimes twenty lines at a time without premeditation and even against my will.” Johann Wolfgang von Goethe claimed to have written his novella The Sorrows of Young Werther with practically no conscious input, as though he were holding a pen that moved on its own.

The emerging understanding of the brain profoundly changes our view of ourselves, shifting us from an intuitive sense that we are at the center of the operations to a more sophisticated, illuminating, and wondrous view of the situation. And indeed, we’ve seen this sort of progress before.

For example, it seemed obvious that your senses give you an accurate representation of the outside world—

but by 1833 a German physiologist named Johannes Peter Müller (1801–1858) had noticed something puzzling. If he shone light in the eye, put pressure on the eye, or electrically stimulated the nerves of the eye, all of these led to similar sensations of vision—that is, a sensation of light rather than of pressure or electricity. This suggested to him that we are not directly aware of the outside world, but instead only of the signals in the nervous system.8 In other words, when the nervous system tells you that something is “out there”—such as a light—that is what you will believe, irrespective of how the signals get there.

With the dawning of the industrial age, intellectuals were thinking about machines. Just as people apply the computer metaphor now, the machine metaphor permeated popular thought then. By this point, the later part of the nineteenth century, advances in biology had comfortably attributed many aspects of behavior to the machinelike operations of the nervous system. Biologists knew that it took time for signals to be processed in the eyes, travel along the axons connecting them to the thalamus, then ride the nerve highways to the cortex, and finally become part of the pattern of processing throughout the brain.

The young Freud went to medical school, drawn there more by scientific research than clinical application. He specialized in neurology and soon opened a private practice in the treatment of psychological disorders. By carefully examining his patients, Freud came to suspect that the varieties of human behavior were explicable only in terms of unseen mental processes, the machinery running things behind the scenes. Freud noticed that often with these patients there was nothing obvious in their conscious minds driving their behavior, and so, given the new, machinelike view of the brain, he concluded that there must be underlying causes that were hidden from access. In this new view, the mind was not simply equal to the conscious part we familiarly live with; rather it was like an iceberg, the majority of its mass hidden from sight.

While the popularity and details of psychoanalysis have changed quite a bit, Freud’s basic idea provided the first exploration of the way in which hidden states of the brain participate in driving thought and behavior. Freud and Breuer jointly published their work in 1895, but Breuer grew increasingly disenchanted with Freud’s emphasis on the sexual origins of unconscious thoughts, and eventually the two parted ways.

Freud went on to publish his major exploration of the unconscious, The Interpretation of Dreams, in which he analyzed his own emotional crisis and the series of dreams triggered by his father’s death. His self-analysis allowed him to reveal unexpected feelings about his father—for example, that his admiration was mixed with hate and shame. This sense of the vast presence below the surface led him to chew on the question of free will. He reasoned that if choices and decisions derive from hidden mental processes, then free choice is either an illusion or, at minimum, more tightly constrained than previously considered.

By the middle of the twentieth century, thinkers began to appreciate that we know ourselves very little. We are not at the center of ourselves, but instead—like the Earth in the Milky Way, and the Milky Way in the universe—far ...

Intuition suggests that you open your eyes and voilà: there’s the world, with all its beautiful reds and golds, dogs and taxicabs, bustling cities and floriferous landscapes. Vision appears effortless and, with minor exceptions, accurate. There is little important difference, it might seem, between your eyes and a high-resolution digital video camera. For that matter, your ears seem like compact microphones that accurately record the sounds of the world, and your fingertips appear to detect the three-dimensional shape of objects in the outside world. What intuition suggests is dead wrong. So let’s see what’s really happening.

You’re not perceiving what’s out there. You’re perceiving whatever your brain tells you.

In the 1960s, the neuroscientist Paul Bach-y-Rita at the University of Wisconsin began chewing on the problem of how to give vision to the blind.25 His father had recently had a miraculous recovery from a stroke, and Paul found himself enchanted by the potential for dynamically reconfiguring the brain. A question grew in his mind: could the brain substitute one sense for another? Bach-y-Rita decided to try presenting a tactile “display” to blind people.26 Here’s the idea: attach a video camera to someone’s forehead and convert the incoming video information into an array of tiny vibrators attached to their back. Imagine putting this device on and walking around a room blindfolded. At first you’d feel a bizarre pattern of vibrations on the small of your back. Although the vibrations would change in strict relation to your own movements, it would be quite difficult to figure out what was going on. As you hit your shin against the coffee table, you’d think, “This really is nothing like vision.” Or isn’t it? When blind subjects strap on these visual-tactile substitution glasses and walk around for a week, they become quite good at

navigating a new environment. They can translate the feelings on their back into knowing the right way to move. But that’s not the stunning part. The stunning part is that they actually begin to perceive the tactile input—to see with it. After enough practice, the tactile input becomes more than a cognitive puzzle that needs translation; it becomes a direct sensation.27 If it seems strange that nerve signals coming from the back can represent vision, bear in mind that your own sense of vision is carried by nothing but millions of nerve signals that just happen to travel along different cables. Your brain is encased in absolute blackness in the vault of your skull. It doesn’t see anything. All it knows are these little signals, and nothing else. And yet you perceive the world in all shades of brightness and colors. Your brain is in the dark but your mind constructs light.

The apparatus reminds us that we see not with our eyes but rather with our brains.

Here’s an amazing consequence of the brain’s plasticity: in the future we may be able to plug new sorts of data streams directly into the brain, such as infrared or ultraviolet vision, or even weather data or stock market data.34 The brain will struggle to absorb the data at first, but eventually it will learn to speak the language. We’ll be able to add new functionality and roll out Brain 2.0.

In the awake state, internal activity is the basis for imagination and hallucinations.

The deep secret of the brain is that not only the spinal cord but the entire central nervous system works this way: internally generated activity is modulated by sensory input.

Ten percent of people with eye disease and visual loss will experience visual hallucinations.

For all we know, we hallucinate all the time.

This is a specific example of the broader concept of internal models of the outside world. The brain internally simulates what will happen if you were to perform some action under specific conditions. Internal models not only play a role in motor acts (such as catching or dodging) but also underlie conscious perception.

As early as the 1940s, thinkers began to toy with the idea that perception works not by building up bits of captured data, but instead by matching expectations to incoming sensory data.45

One of the earliest examples of this framework came from the neuroscientist Donald MacKay, who in 1956 proposed that the visual cortex is fundamentally a machine whose job is to generate a model of the world.46 He suggested that the primary visual cortex constructs an internal model that allows it to anticipate the data streaming up from the retina (see the appendix for an anatomical guide). The cortex sends its predictions to the thalamus, which reports on the difference between what comes in through the eyes and what was already anticipated. The thalamus sends back to the cortex only that difference information—that is, the bit that wasn’t predicted away. This unpredicted information adjusts the internal model so there will be less of a mismatch in the future. In this way, the brain refines its model of the world by paying attention to its mistakes. MacKay pointed out that this model is consistent with the anatomical fact that there are ten times as many fibers projecting from the primary visual cortex back to the visual thalamus as there are going the other direction—just what you’d expect if detailed expectations were sent from the cortex to the thalamus and the forward-moving information represented only a small signal carrying the difference. What all this tells us is that perception reflects the active comparison of sensory inputs with internal predictions. And this gives us a way to understand a bigger concept: awareness of your surroundings occurs only when sensor...

This predictability that you develop between your own actions and the resulting sensations is the reason you cannot tickle yourself. Other people can tickle you because their tickling maneuvers are not predictable to you. And if you’d really like to, there are ways to take predictability away from your own actions so that you can tickle yourself. Imagine controlling the position of a feather with a time-delay joystick: when you move the stick, at least one second passes before the feather moves accordingly. This takes away the predictability and grants you the ability to self-tickle. Interestingly, schizophrenics can tickle themselves because of a problem with their timing that does not allow their motor actions and resulting sensations to be correctly sequenced.47

Take Anton’s syndrome,

Those with Anton’s syndrome are not pretending they are not blind; they truly believe they are not blind. Their verbal reports, while inaccurate, are not lies. Instead, they are experiencing what they take to be vision, but it is all internally generated.

It is not only vision and hearing that are constructions of the brain. The perception of time is also a construction.

Time perception is an active area of investigation in my laboratory and others, but the overarching point I want to make here is that our sense of time—how much time passed and what happened when—is constructed by our brains. And this sense is easily manipulated, just like our vision can be.

To the extent that consciousness is useful, it is useful in small quantities, and for very particular kinds of tasks. It’s easy to understand why you would not want to be consciously aware of the intricacies of your muscle movement, but this can be less intuitive when applied to your perceptions, thoughts and beliefs, which are also final products of the activity of billions of nerve cells. We turn to these now.

as the mere exposure effect,

illusion-of-truth effect:

The illusion-of-truth effect highlights the potential danger for people who are repeatedly exposed to the same religious edicts or political slogans.

With time, the subjects began to realize that each deck had a character to it: two of the decks were “good,” meaning that the subjects would make money, while the other two were “bad,” meaning they would end up with a net loss.

twenty-five draws

The investigators also measured the subject’s skin conductance response, which reflects the activity of the autonomic (fight-or-flight) nervous system.

autonomic nervous system

This spike was detectable by about the thirteenth card draw.

So some part of the subjects’ brains was picking up on the expected return from the decks well before the subjects’ conscious minds could access that information.

This means that conscious knowledge of the situation was not required for making advantageous decisions.

Amazingly, even after these patients consciously realized which decks were bad, they still continued to make the wrong choices.

In other words, the gut feeling was essential for advantageous decision making.

This led Damasio to propose that the feelings produced by physical states of the body come to guide ...

Body states become linked to outcomes of events in the world. When something bad happens, the brain leverages the entire body (heart rate, contraction of the gut, weakness of the muscles, and so on) to register that feeling, and that feeling becomes associated with the event.

If you cannot always elicit a straight answer from the unconscious brain, how can you access its knowledge? Sometimes the trick is merely to probe what your gut is telling you. So the next time a friend laments that she cannot decide between two options, tell her the easiest way to solve her problem: flip a coin. She should specify which option belongs to heads and which to tails, and then let the coin fly. The important part is to assess her gut feeling after the coin lands. If she feels a subtle sense of relief at being “told” what to do by the coin, that’s the right choice for her. If, instead, she concludes that it’s ludicrous for her to make a decision based on a coin toss, that will cue her to choose the other option.

And this is where consciousness plays a role. Conscious parts of the brain train other parts of the neural machinery, establishing the goals and allocating the resources.

This is what consciousness does: it sets the goals, and the rest of the system learns how to meet them.

In his book Your Brain Is (Almost) Perfect, neuroscientist Read Montague highlights the impressive energy efficiency of the brain, comparing chess champion Garry Kasparov’s energy usage of about 20 watts to the consumption of his computerized competitor Deep Blue, in the range of thousands of watts. Montague points out that Kasparov played the game at normal body temperature, while Deep Blue was burning hot to the touch and required a large collection of fans to dissipate the heat. Human brains run with superlative efficiency.

This trick of burning tasks into the circuitry is fundamental to how brains operate: they change the circuit board of their machinery to mold themselves to their mission. This allows a difficult task that could be accomplished only clumsily to be achieved with rapidity and efficiency. In the logic of the brain, if you don’t have the right tool for the job, create it.

Note that baby koalas—known as joeys—eat their mother’s fecal matter to obtain the right bacteria for their digestive systems.

These bacteria are necessary for the joeys to survive on otherwise-poisonous eucalyptus leaves.