The Ghost in the Machine: Mental Maps and the Fragile Unity of the Mind

What dissolves the imaginary problem is seeing through both the problem and the one who seems to have it. (Joan Tollifson)

Imagine yourself as an alien scientist trying to gain insight into my subjective experience by investigating me as a biological organism. As I am laying in a high-resolution fMRI machine, you are getting a clear, unobstructed, dynamic view of my neural firings and hear a flat electronic voice transcribing my speech. But no amount of information about me as a system would suffice to catch a glimpse of my awareness. You would still have no idea what it would feel like to be me — living in my private world of which I am the center. Both perspectives on me are valid and complementary, but your perception of me as a complex system is vastly different from my experience of myself as a sentient being, an intentional agent, an autonomous self.

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Our brain is the most complex system in the known universe. It is also the one we have been interacting with most often. Given our challenges with understanding complex systems, our most deeply ingrained — and most consequential — misconceptions must be about ourselves.

Nowadays, it seems natural to assume that our self is intimately dependent on the brain. It has long been observed that damages to particular brain areas reliably predict declines in the corresponding mental functions. Neurosurgery has further confirmed these observations. Modern science has developed refined non-invasive procedures for analyzing this dependency by systematically mapping the activity in well-defined brain areas to specific behaviors and experiences. We now have compelling evidence that sensations, perceptions, thoughts, and feelings are all caused by the patterns of activity among neurons. Mind somehow emerges from the interaction of loosely arranged basic cells that follow simple rules of interaction.

Upon reflection, however, a conclusion that a physical brain can produce an intangible mind is not at all intuitive. It may be easy to see the heart as a pump, the stomach as a container, and the kidney as a filter. But why would a small bundle of wrinkly gray matter house the seemingly immaterial substrate?

Indeed, the self was traditionally equated with the “soul” and believed to reside in the heart, alongside reason, emotion, and other mental faculties. The first mummification step in ancient Egypt, according to Christof Koch, was “to scoop out the brain and discard it” while “the heart, the liver and other internal organs were carefully extracted and preserved so that the Pharaoh had access to everything he needed in his afterlife.” Even Aristotle viewed the heart as the home of intelligence, and the brain — as a blood-cooling device. (As a careful observer, Aristotle noticed that the blood exiting the brain was considerably cooler than the blood entering it — which we now understand as being due to the brain’s intense energy consumption.) It was not until the 2nd century A.D. that a physician Galen first argued that “the vital spirit” animating humans flows up through the body into the head, where it “becomes purified into thought, sensation, and movement.” Even in Galen’s mind, however, the brain’s mushy gray matter served merely as a filter and a pump. Later cultures viewed the mind through the lens of whatever technology they were most familiar with, metaphorically likening the brain to a mechanical clockwork, a telephone switchboard, a computer, the internet, and nowadays, to convolutional neural networks.

Mental breakdowns and brain disorders are “cracks in the façade of the self” (in the words of Anil Ananthaswamy) that let us examine neural processes that are mostly impenetrable otherwise. The very same abnormal experience may appear terrifying to a psychiatric patient, amusing to a psychedelic explorer, inspirational to a meditator, insightful to a philosopher, and informative to a neuroscientist. Looking under the hood of our brain may help us to not only gain a deeper understanding of our mind but also become more accepting of ourselves at the human, personal level. Rather than “deconstructing” or eliminating the self, we may gain a more holistic understanding of the magic glue that holds it together and makes it struggle to preserve its current shape.

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To make the navigation of our environment more efficient, our brain directs visual, auditory, and proprioceptive sensory inputs to the adjacent clusters of neurons. Neuroscientists capture this spatial coherence in the form of brain maps. Just as the country borders, brain maps come about by happenstance and continue being shaped by active inputs from the body, points out David Eagleman. The notion of a map as a discrete entity is merely a helpful abstraction, agrees Antonio Damasio, as our mental states always involve multiple brain regions. Nor does the deterioration of specific mental functions due to the damage to certain brain areas imply that those functions are somehow “located” there. (London Bridge’s falling down would have led to significant economic disruptions, yet the economy of medieval England was by no means located on the bridge.) Nevertheless, the notion of brain maps may help rule out implausible conjectures, suggest intriguing hypotheses, and provide useful insights.

Well-defined maps support our ability to detect progressively smaller sensory differences. Due to the poor differentiation across infants’ brain maps, their chaotic and awkward movements engage many muscles at once. However, as they mature and become aware of subtle distinctions in their sensations, the movements become more economic and precise. Since sensory data can be corrupted by noise, the brain must figure out how to use the incoming information for updating the maps. One approach is to rely on consistency over time: If a change is lasting, the map is worth updating. For example, if you grew up with scoliosis and got your spine aligned as an adult, you would feel tilted while walking straight until your brain has adjusted. Meanwhile, tilting your spine back into the habitual curve would initially “feel right.”

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The boundaries of brain maps are not fixed. Though somewhat delineated, their outlines are often “porous,” as a map may “slide” onto an adjacent one. While we tend to think of neurons as cooperating happily, like ants in a colony, points out Eagleman, they could be more accurately viewed as fiercely competing for resources to stay alive. This is why the “homunculus” in medical textbooks looks so strange: The body areas that send more sensory information to the brain (such as fingers and lips as opposed to torso and thighs) win more of the brain real estate. Even if you merely tie two of your fingers together and let them operate as a unit for some time, their maps will eventually merge into a single area.

According to Eagleman, any patch of the cortex is “pluripotent,” meaning that it can develop a variety of functions depending on what inputs are plugged into it. (The term was originally used to describe differentiated cells that can sometimes be reprogrammed in adulthood.) For example, when an animal’s visual inputs are experimentally “redirected” to the part of the brain normally involved in hearing, the “rewired” animal appears to “see” with its auditory cortex. Apparently, its brain interprets the sound as normal vision. Similarly, observes Eagleman, the visual cortex of those who were born blind is completely taken over by other senses such as smell and taste. Even when people with normal vision are blindfolded for as little as an hour, their visual cortex temporarily becomes active when they perform tasks with their fingers or when they listen to sounds. The auditory cortex of deaf people also becomes employed for vision and other perceptual tasks unrelated to hearing.

Similarly, when an amputated hand stops being a source of continuous sensory inputs, its original brain map is encroached upon by the surrounding areas. Those greedy neighbors happily move in to take over the abandoned land where the hand used to be. Since the map of the face happens to be located next to the map of the hand (rather than that of the neck, as one would expect), a map of the hand (with distinct fingers) may be felt on the face, and a map of the face may appear on the palm. What if a brain area such as the “visual” cortex is only visual because of the data it receives, wonders Eagleman?

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Brain maps that are naturally assembled in unusual ways may produce remarkable sensory experiences. Synesthesia describes surreal abilities to taste colors, see music, hear shapes, or touch emotions in various combinations. “The sound of colors,” wrote Wassily Kandinsky, “is so definite that it would be hard to find anyone who would express bright yellow with bass notes, or dark lake with the treble.” Similarly, people with color-number synesthesia associate numbers with colors, imbuing each number with its unique “personality.” It turns out that the brain maps for colors and numbers share borders. Synesthesia may thus be caused by a “crosstalk” between these normally separated areas.

An complementary hypothesis, suggested by Eagleman, blames synesthesia on our reduced ability to modify an association once it has been set. For example, once a child associates a letter with a color in which it is drawn on a letter block, it sticks, becoming the source of color-number synesthesia. The spatial proximity probably helps reinforce the association. Incidentally, our language is a special case of synesthesia, which combines concepts and images with otherwise meaningless noises.

Across the animal kingdom, we find all kinds of strange peripheral devices. As random mutations introduce new sensors, the brains simply figure out how to exploit them based on a few general principles. But for the new sensor to become operational, the adaptation doesn’t have to take multiple generations. Just as you don’t need to buy a new computer for each new hardware component, your brain doesn’t need an upgrade to support a new sensor. For example, when an extra eye is transplanted on one side of a tadpole, the two eyes on that side split control over the original brain map, enabling full vision in the new eye.

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Our brain has a mysterious ability (called perceptual binding) to weave together sensory inputs to create a holistic perception. From a distance, an impressionist painting may look like a woman holding a child in front of their house. When you zoom in, however, you may notice that each one is painted with just a few brushstrokes (which you initially saw as pieces of clothing and faces). Outside of the context created by the entire painting, the patches of color would remain meaningless. Combining shapes with colors — to see green as going with a frog — also requires a binding step. When you look at your friend, your brain combines parts of the face (eyes, nose, and mouth) into a single recognizable image. When you hear a person talking, your brain further merges the face and the movements of her mouth with the sounds coming out of it to create a seamless multimedia experience.

The same is true of our perception of ourselves. Only in anatomy textbooks and sci-fi thrillers is the brain isolated from the body and confined to the head. In reality, it is always attached to the senses, and through them, to the world outside. Despite the moment-to-moment sensory flux, our body usually feels like a single whole. Yet the only reason why the hand you see coincides with the hand you feel, observed William James over a century ago, is that “the original sensations… coalesced together into one and the same space.” The sensations from your entire body are fused. There is unity to everything you are at any moment. Your embodied self — an intangible sentient entity behind your eyes that appears to animate your body and mind — is continuously constructed from the real-time coordination of your senses.

Our brain’s representation of the body, however, can be confused by scrambling the inputs from different senses. When our body image doesn’t match up with the sensory inputs, our inner harmony is disrupted. It may be impossible for most of us to imagine what it would feel like to become incapable of combining the features of a perceived object (such as its color and texture) into a single entity. Yet there is no single place in the brain where the incoming information is being integrated to create a complete perception. Though we may routinely take it for granted, the apparent unity of consciousness is one of the most significant achievements of evolution. In this regard, we are like our alien friend, the octopus.

However, the similarity ends there. The octopus’s body is not a unified entity controlled by the brain, observes Peter Godfrey-Smith. Rather, its brain is spread throughout its body. Most of the octopus’s neurons are in its arms, equipped with their own sensors and controllers, which enjoy considerable independence. Besides the sense of touch, the arms can also smell and taste chemicals. Even an arm that has been surgically removed can perform basic motions like reaching and grasping. The octopus may not even track the location of its arms. To some extent, the central brain guides its arms, but otherwise, it just watches them go. They sense and respond independently, only briefly losing autonomy when the octopus “pulls itself together” and imposes central control. An entire bee has only a million neurons, while each octopus’ arm has tens of millions of them. Could the arms have their own experiences?

An uncontrolled movement of an object is usually a sign that it isn’t part of our self — but for the octopus, this distinction must be blurred. Its arms are partly “self,” directed and used to manipulate things, and partly “non-self,” roaming freely as the agents of their own. The octopus’ brain is like a jazz conductor, orchestrating creative artists who are willing to accept only so much direction. Despite feeling unified, our self may also be an elaborate performance by an enormous ensemble of non-sentient players rather than a lonely ghost lurking in the guts of the neural machine.

This story is best enjoyed as part of the The Uncharted Present series of articles, starting with an intro. If that’s how you got here, please continue to the next one.

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