Consciousness: Confessions of a Romantic Reductionist (The MIT Press)

by Christof Koch

Consciousness does not appear in the equations that make up the foundations of physics, nor in chemistry’s periodic table, nor in the endless ATGC molecular sequences of our genes. Yet both of us—I, the author of these lines, and you, the reader—are sentient. That is the universe in which we find ourselves, a universe in which particular vibrations of highly organized matter trigger conscious feelings. It seems as magical as rubbing a brass lamp and having a djinn emerge who grants three wishes.

What is the difference that makes a difference? In philosophy, the difficulty of explaining why somebody can feel anything is often referred to as the Hard Problem. The term was coined by the philosopher David Chalmers. He made his reputation in the early 1990s by a closely argued chain of reasoning, leading him to conclude that conscious experience does not follow from the physical laws that rule the universe. These laws are equally compatible with a world without consciousness or with a different form of consciousness. There will never be a reductionist, mechanistic account of how the objective world is linked to the subjective one. The term Hard Problem, with its capital H, as in “Impossibly Hard,” subsequently went viral. Nobody disputes that the physical and the phenomenal worlds are closely linked in billions of people every day of their lives, but why this should be so is the puzzle.

Many people believe that science leaches meaning out of human actions, hopes, and dreams, leaving desolation and emptiness in their place. The pioneering molecular biologist Jacques Monod expressed this forlorn sentiment chillingly: Man must at last wake up out of his millenary dream and discover his total solitude, his fundamental isolation. He must realize that, like a gypsy, he lives on the boundary of an alien world; a world that is deaf to his music, and as indifferent to his hopes as it is to his sufferings and his crimes.

I now realize that what drew me to studying consciousness was a compelling and entirely subterranean desire to justify my instinctual belief that life is meaningful.

As recounted in The Eighth Day of Creation, Horace Freeland Judson’s brilliant history of molecular biology, Francis subsequently established himself as the field’s chief intellect.

As Sigmund Freud, Pierre Janet, and others realized in the late nineteenth century, much of what goes on in our head is inaccessible to our mind—is not conscious. Indeed, when we introspect, we routinely deceive ourselves, because we only tap into a minute fraction of what is going on in our head. This deception is why so much of philosophy about the self, the will, and other aspects of our mind has been barren for more than two thousand years. Yet, as I shall describe, the unconscious can profoundly influence our behavior. I also dwell on the related problem of free will, the feeling of having initiated an action, and on how physics, psychology, and neurosurgery are untangling this metaphysical knot. Without much fanfare, discoveries in these fields have solved a key aspect of the free will problem.

The theory of integrated information, developed by the neuroscientist and psychiatrist Giulio Tononi, starts with two basic axioms and proceeds to account for the phenomenal in the world. It is not mere speculative philosophy, but leads to concrete neurobiological insights, to the construction of a consciousness-meter that can assess the extent of awareness in animals, babies, sleepers, patients, and others who can’t talk about their experiences.

This dynamic universe is governed by the second law of thermodynamics: The entropy of any closed system never decreases; or, in other words, the universe is unfolding to be maximally disordered and uniform. But this does not preclude the formation of stable islands of order that feed upon the surrounding ocean of free energy. The relentless operation of this law created the statistical certainty that on some such isles in the cosmos, long-chained, complex molecules would eventually arise.

The continuing complexification of brains, to use Teilhard de Chardin’s term, enhanced consciousness until self-consciousness emerged: awareness reflecting upon itself. This recursive process started millions of years ago in some of the more highly developed mammals. In Homo sapiens, it has achieved its temporary pinnacle.

But complexification does not stop with individual self-awareness. It is ongoing and, indeed, speeding up. In today’s technologically sophisticated and intertwined societies, complexification is taking on a supraindividual, continent-spanning character. With the instant, worldwide communication afforded by cell phones, e-mail, and social networking, I foresee a time when humanity’s teeming billions and their computers will be interconnected in a vast matrix—a planetary Übermind.

Why was I motivated—consciously or otherwise—to pursue certain problems? And, why did I adopt a particular scientific stance? It is, after all, in the choice of what we work on that we reveal much about our inner drives and motives.

Midway in the journey of our life I came to myself in a dark wood, for the straight way was lost.

Humanity is not condemned to wander forever in an epistemological fog, knowing only the surface appearance of things but never their true nature. We can see something; and the longer we gaze, the better we comprehend.

Michael and I calculated the position of Uranus on a star map to the background strains of Wagner’s The Flying Dutchman. What elation I felt when, pointing the scope to the estimated azimuth and elevation in the sky, the shimmering planet gently drifted into view. What a terrific confirmation of order in the universe!

Growing up in different countries, attending different schools, and learning different languages allowed me, more so than my less mobile friends, to see beyond the peculiarities and distinctiveness of any one culture and appreciate the underlying universal traits. This was one of many formative reasons that made me, by the time I left home, want to be a physicist.

one can be a great scientist, an esthete, a musician, a bon vivant, and a mensch, all at the same time.

Like all organs, the nervous system is made out of billions of networked cells, the most important of which are neurons. Just like there are kidney cells that are quite distinct from blood or heart cells, so there are different types of neurons, maybe as many as a thousand.

We professors spend the bulk of our time on investigations—thinking, reasoning and theorizing, computing and programming, talking thru ideas with colleagues and co-workers, reading the commodious literature, contributing ourselves to it, speaking at seminars and conferences, generating the countless grant proposals that feed the research machinery and keep it lubricated, and, of course, supervising and mentoring students and postdoctoral fellows who design, fabricate, measure, shake, stir, image, scan, record, analyze, program, debug, and compute. I’m the chieftain of a band of about two dozen such researchers.

The brain is a highly evolved organ, yet it is also a physical system that obeys ironclad laws of conservation of energy and of electrical charge. Gauss’s and Ohm’s laws regulate the distribution of charges inside and outside of nerve cells and their associated electric fields. All the synaptic and spiking processes described above contribute to the electrical potential that is picked up by electrodes stuck into the brain’s gray matter. If tens of thousands of neurons and their millions of synapses are active, their contributions add up to something called the local field potential. The distant echo of this electrical activity is visible in the never-ceasing peaks and troughs recorded outside the skull by an electroencephalograph (EEG). The local field potential, in turn, feeds back onto individual neurons. We are now learning that this feedback forces neurons to synchronize their activity.

Darwin’s theory of evolution by natural selection—and although it is an exceedingly powerful explanatory framework, evolutionary theory is open-ended, and not predictive. Instead, the life sciences have lots of heuristics, semi-exact rules, that capture and quantify phenomena at one particular organismal scale—such as the biophysical modeling that I worked on for my thesis—without aspiring to universality.

Francis was an intellectual giant, with the clearest and deepest mind I have ever met. He could take the same information as anybody else, read the same papers, yet come up with a totally novel question or inference. The neurologist and author Oliver Sacks, a good friend of us both, recollects that the experience of meeting Francis was “a little like sitting next to an intellectual nuclear reactor . . . . I never had a feeling of such incandescence.” It has been said that Arnold Schwarzenegger, in his heyday as Mr. Universe, had muscles in places where other people didn’t even have places. This bon mot, transcribed to the rational mind, applied to Francis.

Francis was a reductionist writ large. He fiercely opposed any explanation that smacked even remotely of religion or woolly-headed thinking, an expression he was fond of using.

How did evolution convert the water of biological tissue into the wine of consciousness? —Colin McGinn, The Mysterious Flame (1999)

The seventeenth-century French physicist, mathematician, and philosopher René Descartes, in his Discourse on the Method of Rightly Conducting the Reason, and Seeking Truth in the Sciences, sought ultimate certainty. He reasoned that everything was open to doubt, including whether the outside world existed or whether he had a body. That he was experiencing something, though, even if the precise character of what he was experiencing was delusional, was a certainty. Descartes concluded that because he was conscious, he existed: Je pense, donc je suis, later translated as cogito, ergo sum, or I think, therefore I am.

The singular point of view of the conscious, experiencing observer is called the first-person perspective. Explaining how a highly organized piece of matter can possess an interior perspective has daunted the scientific method, which in so many other areas has proved immensely fruitful.

Biologists can’t yet specify the detailed molecular programs inside a single fertilized mammalian egg that turn it into the trillion cells making up the liver, muscle, brain, and other organs of a fully formed individual.

The artificial genome successfully commanded the donor cell’s protein-making machinery, and the new organism, dubbed Mycoplasma mycoides JCVI-syn1.0, proceeded to replicate generation after generation. Although the creation of a new bacterial species does not make a golem, it is nevertheless an amazing act, a watershed moment in history.

Were our minds and senses so expanded, strengthened, and illuminated, as to enable us to see and feel the very molecules of the brain; were we capable of following all their motions, all their groupings, all their electric discharges, if such there be; and were we intimately acquainted with the corresponding states of thought and feeling, we should be as far as ever from the solution of the problem, “How are these physical processes connected with the facts of consciousness?”

But how does nervous tissue acquire an interior, first-person point of view?

Yet the resistance of consciousness to a reductionist understanding delights much of the public. They denigrate reason and those who serve its call, for a complete elucidation of consciousness threatens long and dearly held beliefs about the soul, about human exceptionalism, about the primacy of the organic over the inorganic. Dostoyevsky’s Grand Inquisitor understands this mind-set well: “There are three powers, three powers alone that are able to conquer and hold captive for ever the conscience of these impotent rebels for their happiness—those forces are miracle, mystery, and authority.”

The same is true of the 100 million neurons that crisscross the inner lining of your gut—the enteric nervous system, sometimes called the second brain. Those neurons go about their business quietly, taking care of nutrient extraction and waste disposal in the gastrointestinal tract. Things you would rather not know about. On occasion, the enteric system acts up—you feel butterflies in your stomach before a crucial job interview or nauseated after a large meal. That information is communicated via the (gastric) vagus nerve to the cerebral cortex, which then generates the nervous or heavy sensation. The second brain in your gut doesn’t directly give rise to consciousness.

Your body might harbor several autonomous minds, forever isolated, as distant as the dark side of the Moon. Right now, this possibility can’t be completely discounted; however, given the limited, stereotyped behaviors of the enteric nervous system, it appears to be subservient to the brain proper, with no capability for independent experience.

I seek a way of answering such questions based on physical principles, on looking at the actual wiring diagram of a brain and deducing from its circuits the sensations that the brain is capable of experiencing. Not just the existence of conscious states, but their detailed character as well. Perhaps you think this feat is beyond science? Don’t. Poets, songwriters, and security officials bemoan the impossibility of knowing the mind of anybody else. Although that may be true when looking from the outside, it is not true if I have access to a person’s entire brain, with all of its elements. With the correct mathematical framework, I should be able to tell exactly what she or he is experiencing. Like it or not, true mind reading is, at least in principle, possible. More on that in chapters 5 and 9.

What survival value is attached to the inner screen of our mental experiences? What is the function of consciousness, the function of qualia?

Whereas consciousness is needed to learn these skills, the point of training is that you don’t need to think about them anymore; you trust the wisdom of your body and let it take over.

Francis Crick and I postulated the existence of an army of simple-minded zombie agents inside each person. These agents are dedicated to stereotypical tasks that can be automated and executed without conscious supervision.

It may well be that unconscious processes can also plan, but much more slowly than conscious processes or without looking quite as far into the future.

In this spirit, let me offer four different definitions of consciousness. Like the Buddhist fable of the blind men, each describing different aspects of the same elephant, each captures an important facet of consciousness, with none of them painting a complete picture.

Whether the two most popular species in biology labs—the roundworm Caenorhabditis elegans, with its 302 nerve cells, and the fruit fly Drosophila melanogaster, with its 100,000 neurons—have any phenomenal states is difficult to ascertain at the moment. Without a sound understanding of the neuronal architecture necessary to support consciousness, we cannot know whether there is a Rubicon in the animal kingdom that separates sentient creatures from those that do not feel anything.

When you are truly engaged with the world, you are only dimly aware of yourself. I feel this most acutely when I climb mountains, cliffs, and desert towers. On the high crag, life is at its most intense. On good days, I experience what the psychologist Mihaly Csikszentmihalyi calls flow. It is a powerful state in which I am exquisitely conscious of my surroundings, the texture of the granite beneath my fingers, the wind blowing in my hair, the Sun’s rays striking my back, and, always, always, the distance to the last hold below me. Flow goes hand-in-hand with smooth and fluid movements, a seamless integration of sensing and acting. All attention is on the task at hand: The passage of time slows down, and the sense of self disappears. That inner voice, my personal critic who is always ready to remind me of my failings, is mute. Flow is a rapturous state related to the mind-set of a Buddhist lost in deep meditation.

The perennial habit of introspection has led many intellectuals to devalue the unreflective, nonverbal character of much of life and to elevate language to the role of kingmaker. Language is, after all, their major tool.

Imagine that you are looking at a red cube, mysteriously left in the desert sand, with a butterfly fluttering above it. Your mind apprehends the cube in a flash. It performs this feat because the brain activates specialized cortical neurons that represent color and combines them with neurons that encode the percept of depth, as well as neurons that encode the orientation of the various lines that make up the cube. The minimal set of such neurons that causes the conscious percept is the neural correlate of consciousness for perceiving this alien object.

What about the cerebellum, the little brain at the back of the head, underneath the cerebral cortex? The moniker “little” is ironic, because the cerebellum has 69 billion nerve cells, more than four times the number in the celebrated cerebral cortex, which hogs all of the limelight.

Every phenomenal, subjective state is caused by a particular physical mechanism in the brain. There is a circuit for seeing your grandmother in a picture or in life, another one for hearing the sound of the wind whispering through pine trees on a mountaintop, and a third one for the vicarious rush when rapidly weaving on a bicycle through city traffic.

Depending on the location and intensity, this external stimulus can trigger a poignant memory, a song last heard years before, the feeling of wanting to move a limb or the sensation of movement.

During sleep, you have vivid, sometimes emotionally wrenching, phenomenal experiences, even if you don’t recall most of them. Your eyes are closed, yet the dreaming brain constructs its own reality. Except for rare “lucid” dreams, you can’t tell the difference between dreaming and waking consciousness. Dreams are real while they last. Can you say more of life?

The adult brain, even if cut off from most input and output, is all that is needed to generate that magical stuff, experience.

or-none pulses described in chapter 2. The output of the eye does not depend on whether the owner of the eyeball is conscious. As long as the eyelids are open, the optic nerve faithfully signals what is out there and passes this on to downstream structures in the cerebral cortex. This activity ultimately triggers the formation of a stable coalition of active cortical neurons that conveys the conscious percept of a red ace.

The MRI scanner generates a powerful magnetic field, about 100,000 times stronger than Earth’s magnetic field. The nuclei of certain elements, including hydrogen, behave like miniature bar magnets. When you enter a scanner’s strong magnetic field, the hydrogen nuclei in your body line up with this field. More than half of your body weight is water, which is made up of two hydrogen atoms and one oxygen atom. The MRI scanner sends a brief pulse of radio waves into your skull, knocking the nuclei out of alignment. As the nuclei relax back into their original state, they give off faint radio signals that are detected and processed into a digital image. Such a picture reveals the structure of soft tissue. For example, it demarks the boundary between the brain’s gray and white matter. Magnetic resonance imaging is much more sensitive than X-rays. It has revolutionized medicine by allowing tissue damage, from a tumor to trauma, to be located and diagnosed with negligible risk to the patient.

So, how does the brain respond to things the mind doesn’t see? Remarkably, invisible pictures can leave traces in cortex. Wisps of unconscious processing can be picked up in the primary visual cortex (V1). The primary visual cortex is the terminus for information sent from the eyes. Located just above the bump at the back of the head, it is the first neocortical region evaluating pictorial information. Other sectors of the cerebral cortex respond to suppressed pictures as well—notably the cascade of higher-order visual regions (V2, V3, and so on) that extends beyond the primary visual cortex, and the amygdala, the almond-sized structure that deals with emotional stimuli such as fearful or angry faces.