How Does Consciousness Work?
A Look at the Complex Neural Network that Creates Our Unified Sense of Reality
Our brains look as wonky as Frank Gehry’s Guggenheim Museum in Bilbao, Spain, but as Gehry is apt to point out, the museum doesn’t leak. It works! Gehry is an architectural genius who expanded our imagination of physical structures that perform useful functions. Our brain also has a physical structure that performs useful functions. There is method in the madness of that wonky-looking structure, bits of which we understand, most of which we don’t. Despite centuries of research, nobody fully understands how the convoluted mesh of biological tissue inside our heads produces the experiences of our everyday life. Gazillions of electrical, chemical, and hormonal processes occur in our brain every moment, yet we experience everything as a smoothly running unified whole. How can this be? Indeed, what is the organization of our brain that generates conscious unity?
Everything has an underlying structure; physicists take this truth down to the quantum level. We are constantly taking things apart to see what makes them tick. Things are made up of parts, and so are bodies and brains. In that sense one could say we are built out of modules, which is to say, components that interact to produce the whole functioning entity we are examining. We need to know the parts and not only how they all mesh together but also how they interact.
There is little doubt that in some way the parts of our brain work collectively to produce our mental states and behaviors. On the surface, it seems logical to think that our brain functions as a global unit to produce a single conscious experience. Even the Nobel laureate Charles Sherrington, writing in the early 1900s, described the brain as an “enchanted loom,” suggesting that the nervous system works coherently to create the mystical mind. Yet neurologists at the time would have suggested to him to go on medical rounds. Their clinics were full of patients whose brain injuries told a different story.
Paradoxically, while all of us feel like a single undivided entity (a fact that seems to provide intuitive evidence for Sherrington’s loom), considerable evidence suggests that the brain does not operate in a holistic fashion. Instead, our undivided consciousness is actually produced by thousands of relatively independent processing units, or, more simply, modules. Modules are specialized and frequently localized networks of neurons that serve a specific function.
The neuroscientist, physicist, and philosopher Donald MacKay once commented that it is easier to understand how something works when it is not working properly. From work in the physical sciences, he knew that engineers could more quickly figure out how something, such as a television, worked if the picture was flickering than when it was running smoothly. Similarly, studying broken brains helps us understand better how unbroken ones work. The most compelling evidence for a modular brain architecture arises from the study of patients who have suffered a brain lesion. When damage occurs to localized areas of the brain, some cognitive abilities will be impaired because the network of neurons responsible for that ability no longer functions, while others remain intact, tootling along, performing flawlessly. What is so intriguing about the brain-altered patients is that no matter what their abnormality, they all seem perfectly conscious. If conscious experience depended on the smooth operation of the entire brain, that shouldn’t be what happens. Since this fact—that modules are everywhere—is so central to my thesis, it’s important that we understand how modular the brain truly is.
Missing Modules but Functioning Brains
Take a lobe, any lobe in the brain, and consider people who have suffered a stroke. People with a right parietal lobe injury, for example, will commonly suffer from a syndrome called spatial hemi-neglect. Depending on the size and location of the lesion, patients with hemi-neglect may behave as if part or all of the left side of their world, which may include the left side of their body, does not exist! This could include not eating off the left side of their plate, not shaving or putting makeup on the left side of their face, not drawing the left side of a clock, not reading the left pages of a book, and not acknowledging anything or anyone in the left half of the room. Some will deny that their left arm and leg are theirs and will not use them when trying to get out of bed, even though they are not paralyzed. Some patients will even neglect the left side of space in their imagination and memories. That the deficits vary according to the size and location of the lesion suggests that damage that disrupts specific neural circuits results in impairments in different component processes. Mapping the functional neuroanatomy of these lesions has provided strong evidence for this suggestion.
“Our undivided consciousness is actually produced by thousands of relatively independent processing units.”
Now, here is the kicker: while hemi-neglect can occur when there is actual loss of sensation or motor systems, a version of it can also occur when all sensory systems and motor systems are in good working order—a syndrome known as extinction. In this case each half brain seems to work just fine alone, but it begins to fail when required to work at the same time as the other half. Yet information in the neglected field can be used at a nonconscious level! That means the information is there, but the patient isn’t conscious it is there. Here is how it works. If patients with left hemi-neglect are shown visual stimuli in both their right and left visual fields at the same time, they report seeing only the stimulus on the right. If, however, they are shown only the left visual stimulus, hitting the same exact place on the retina as previously, the left stimulus is perceived normally. In other words, if there is no competition from the normal side, then the neglected side will be noticed and pop into conscious awareness! What is strangest of all is that these patients will deny that there is anything wrong; they are not conscious of the loss of these circuits and their resulting problems.
It appears, then, that their autobiographical self must be derived only from what they are conscious of. And what they are conscious of is dependent on two things. First, they are not conscious of circuits that are not working. It is as if the circuits never existed and consciousness for what the circuits did disappears with the circuit. The second thing is that some sort of competitive processing is happening. Some circuits’ processing makes it into consciousness while others’ does not. In short, conscious experience seems tied to processing that is exceedingly local, which produces a specific capacity, and that processing can also be outcompeted by the processing of other modules and never make it to consciousness. This has astounding implications.
While some patients are not conscious of parts of their body that are actually there, my all-time favorite clinical disorder is the “third man” phenomenon, in which a person feels the presence of another who actually is not there! Known as a “feeling of a presence” (FoP), it is the sensation that someone else is present in a specific spatial location, often just over the shoulder. It is so strong that people will continue to turn their head to glimpse or offer food to the presence. This is not the same as walking down a dark alley and getting creeped out by imagining someone following you. This presence pops up unexpectedly. It is actually a common phenomenon among alpinists and others suffering intense physical exhaustion in extreme conditions.
In his book The Naked Mountain, Reinhold Messner, widely considered to be the greatest mountaineer of all time (he was the first to solo-climb Mount Everest and, incidentally, never uses supplemental oxygen), described what happened in 1970 while he was making his first major Himalayan ascent, of Nanga Parbat, with his brother Günther: “Suddenly there was a third climber next to me. He was descending with us, keeping a regular distance a little to my right and a few steps away from me, just out of my field of vision. I could not see the figure and still maintain my concentration but I was certain there was someone there. I could sense his presence; I needed no proof.” You don’t have to be an exhausted alpinist, however, to experience such a presence. Nearly half of widows and widowers have felt the presence of their deceased spouses. For some, such phenomena are the starting point for tales of apparitions, ghosts, and divine intervention.
Not so, claims the Swiss neurologist and neurophysiologist Olaf Blanke, who came across the phenomenon unexpectedly. He had triggered it with electrical stimulation to the temporal parietal cortex of a patient’s brain while trying to locate the focus of a seizure. He has also studied a bevy of patients who complain of an FoP. He found that lesions in the frontoparietal area are specifically associated with the phenomenon and are on the opposite side of the body from the presence. This location suggested to him that disturbances in sensorimotor processing and multisensory integration may be responsible. While we are conscious of our location in space, we are unaware of the multitude of processes (vision, sound, touch, proprioception, motor movement, etc.) that, when normally integrated, properly locate us there. If there is a disorder in the processing, errors can occur and our brains can misinterpret our location. Blanke and his colleagues have found that one such error manifests itself as an FoP. Recently, they cleverly induced the FoP in healthy subjects by disordering their sensory processing with the help of a robotic arm.
“While we are conscious of our location in space, we are unaware of the multitude of processes. . . that, when normally integrated, properly locate us there.”
When we make a movement, we expect its consequence to occur at a specific time and location in space. You scratch your back, you expect to feel a sensation simultaneously on your back. When the sensation is spatially and temporally matched as expected, your brain interprets the sensation as self-generated. If there is a mismatch, if the signals are spatially and temporally incompatible with self-touch, you rule it as being done by another agent. Now picture yourself blindfolded, arms extended in front of you, with your fingertip in the thimble-like slot of a “master robot” that sends signals to a robotic arm behind your back. Your finger movements control the robotic arm’s movement, which strokes your back as you move your finger. In some trials your finger feels resistance that matches the force with which it is pushing, and in others the resistance is loosey-goosey, not properly correlated to what you are doing. If the sensation on your back is synchronous with your movement, even with your arms extended in front of you, your brain creates an illusion: you will feel as if your body has drifted forward and that you are touching your own back with your finger. If, however, the touch sensation is not synchronous, if it comes a tick late, your brain cooks up something different. Your self-location drifts in the opposite direction, backward away from your fingertip; you feel as if something other than you is touching your back. If, in addition, you also felt no resistance in the fingertip while controlling the arm, this asynchronous touch produces a feeling that another person is behind you touching your back! Blanke, using well-controlled bodily stimulations, demonstrated that sensorimotor conflicts (that is, signals that are spatially and temporally incompatible with physical self-touch) are sufficient to induce the FoP in healthy volunteers. These conflicts were produced by manipulating different localized neural networks—modules.
If the brain worked as a consolidated “enchanted loom,” then removing portions of the brain or stimulating erroneous processing in some circuits would either shut down the system entirely or cause dysfunction across all cognitive realms. In reality, many people can live relatively normal lives even if portions of their brain are missing or damaged. When people have damage to localized brain areas, there almost always appears to be impairment in some, but not all, cognitive domains. For example, a well-developed cognitive domain in humans is language. The language center in most people is housed in the left hemisphere. Two very distinct brain regions within the language center include Broca’s area and Wernicke’s area.
Broca’s area contributes to speech production, whereas Wernicke’s area deals with comprehension or understanding of written and spoken language and helps organize our words and sentences in an understandable way. Specifically, Broca’s area is involved with word articulation, coordinating the muscles in our lips, mouth, and tongue to accurately pronounce words, while Wernicke’s area organizes our words in a comprehensible order before we even speak. People with damage to Broca’s area have difficulty speaking: speech is effortful and comes in bursts, but the words they manage to announce are in a comprehensible order (e.g., “Brains. . . modu. . . lar”), though it may lack proper grammar. Broca patients are aware of their errors and are quickly frustrated. Conversely, people with damage to Wernicke’s area primarily have a comprehension disorder. They have speech with normal prosody and correct grammar, but what they say makes no sense. This shows us that each of these areas has a different and specific job; if that area is damaged, then it can no longer perform the job properly. This unambiguously demonstrates that there is hyperspecific modularity in the brain.
Why did modularity evolve in brains? I once heard the CEO of CocaCola describe the logic of the company’s corporate organization. As the company grew, the executives realized that having a central plant that made all of their product and then shipped it out to the world was crazy, inefficient, and costly. The shipping, the packaging costs, the travel costs of holding management meetings in “corporate headquarters,” and on and on made no sense. Clearly, they should divide the world into regions, build plants in each of those regions, and distribute their product locally. Central planning was out, local control was in. Same for the brain: cheaper and more efficient.
From The Consciousness Instinct: Unraveling the Mystery of How the Brain Makes the Mind.by Michael S. Gazzaniga. Published by Farrar, Straus and Giroux. Copyright © 2018 by Michael S. Gazzaniga. All rights reserved.