The audacious effort to map the brain—and along with it our mental afflictions, from autism to schizophrenia—by a rising star in neuroscience.
“This is complicated stuff, and it is a testament to Dr. Seung’s remarkable clarity of exposition that the reader is swept along with his enthusiasm, as he moves from the basics of neuroscience out to the farthest regions of the hypothetical, sketching out a spectacularly illustrated giant map of the universe of man.”—Abigail Zuger, M.D., New York Times
Every person is unique, but science has struggled to pinpoint where, precisely, that uniqueness resides. Our genome may determine our eye color and even aspects of our character. But our friendships, failures, and passions also shape who we are. The question is: how?
Sebastian Seung is at the forefront of a revolution in neuroscience. He believes that our identity lies not in our genes, but in the connections between our brain cells—our particular wiring. Seung and a dedicated group of researchers are leading the effort to map these connections, neuron by neuron, synapse by synapse. It’s a monumental effort, but if they succeed, they will uncover the basis of personality, identity, intelligence, memory, and perhaps disorders such as autism and schizophrenia.
Connectome is a mind-bending adventure story that presents a daring scientific and technological vision for understanding what makes us who we are, both as individuals and as a species.
“Accessible, witty, imminently logical and at times poetic, Connectome establishes Seung as an important new researcher, philosopher and popularizer of brain science. It puts him on par with cosmology’s Brian Greene and the late Carl Sagan.”—Cleveland Plain Dealer
No road, no trail can penetrate this forest. The long and delicate branches of its trees lie everywhere, choking space with their exuberant growth. No sunbeam can fly a path tortuous enough to navigate the narrow spaces between these entangled branches. All the trees of this dark forest grew from 100 billion seeds planted together. And, all in one day, every tree is destined to die.
This forest is majestic, but also comic and even tragic. It is all of these things. Indeed, sometimes I think it is everything. Every novel and every symphony, every cruel murder and every act of mercy, every love affair and every quarrel, every joke and every sorrow — all these things come from the forest.
You may be surprised to hear that it fits in a container less than one foot in diameter. And that there are seven billion on this earth. You happen to be the caretaker of one, the forest that lives inside your skull. The trees of which I speak are those special cells called neurons. The mission of neuroscience is to explore their enchanted branches — to tame the jungle of the mind (see Figure 1).
Neuroscientists have eavesdropped on its sounds, the electrical signals inside the brain. They have revealed its fantastic shapes with meticulous drawings and photos of neurons. Their discoveries are amazing, but from just a few scattered trees, can we hope to comprehend the totality of the forest?
In the seventeenth century, the French philosopher and mathematician Blaise Pascal wrote about the vastness of the universe:
Let man contemplate Nature entire in her full and lofty majesty; let him put far from his sight the
lowly objects that surround him; let him regard that blazing light, placed like an eternal lamp to
illuminate the world; let the earth appear to him but a point within the vast circuit which that star
describes; and let him marvel that this immense circumference is itself but a speck from the
viewpoint of the stars that move in the firmament.
Shocked and humbled by these thoughts, he confessed that he was terrified by “the eternal silence of these infinite spaces.” Pascal meditated upon outer space, but we need only turn our thoughts inward to feel his dread. Inside every one of our skulls lies an organ so vast in its complexity that it might as well be infinite.
As a neuroscientist myself, I have come to know firsthand Pascal’s feeling of dread. I have also experienced embarrassment. Sometimes I speak to the public about the state of our field. After one such talk, I was pummeled with questions. What causes depression and schizophrenia? What is special about the brain of an Einstein or a Beethoven? How can my child learn to read better? As I failed to give satisfying answers, I could see faces fall. In my shame I finally apologized to the audience. “I’m sorry,” I said. “You thought I’m a professor because I know the answers. Actually I’m a professor because I know how much I don’t know.”
Studying an object as complex as the brain may seem almost futile. The brain’s billions of neurons resemble trees of many species and come in many fantastic shapes. Only the most determined explorers can hope to capture a glimpse of this forest’s interior, and even they see little, and see it poorly. It’s no wonder that the brain remains an enigma. My audience was curious about brains that malfunction or excel, but even the humdrum lacks explanation. Every day we recall the past, perceive the present, and imagine the future. How do our brains accomplish these feats? It’s safe to say that nobody really
Daunted by the brain’s complexity, many neuroscientists have chosen to study animals with drastically fewer neurons than humans. The worm shown in Figure 2 lacks what we’d call a brain. Its neurons are scattered throughout its body rather than centralized in a single organ. Together they form a nervous system containing a mere 300 neurons. That sounds manageable. I’ll wager that even Pascal, with his depressive tendencies, would not have dreaded the forest of C. elegans. (That’s the scientific name for the one-millimeter-long worm.)
Every neuron in this worm has been given a unique name and has a characteristic location and shape. Worms are like precision machines mass-produced in a factory: Each one has a nervous system built from the same set of parts, and the parts are always arranged in the same way.
What’s more, this standardized nervous system has been mapped completely. The result — see Figure 3 — is something like the flight maps we see in the back pages of airline magazines. The four-letter name of each neuron is like the three-letter code for each of the world’s airports. The lines represent connections between neurons, just as lines on a flight map represent routes between cities. We say that two neurons are “connected” if there is a small junction, called a synapse, at a point where the neurons touch. Through the synapse one neuron sends messages to the other.
Engineers know that a radio is constructed by wiring together electronic components like resistors, capacitors, and transistors. A nervous system is likewise an assembly of neurons, “wired” together by their slender branches. That’s why the map shown in Figure 3 was originally called a wiring diagram. More recently, a new term has been introduced — connectome. This word invokes not electrical engineering but the field of genomics. You have probably heard that DNA is a long molecule resembling a chain. The individual links of the chain are small molecules called nucleotides, denoted by the letters A, C, G, and T. Your genome is the entire sequence of nucleotides in your DNA, or equivalently a long string of letters drawn from this four-letter alphabet. Figure 4 shows an excerpt from the three billion letters, which would be a million pages long if printed as a
In the same way, a connectome is the totality of connections between the neurons in a nervous system. The term, like genome, implies completeness. A connectome is not one connection, or even many. It is all of them. In principle, your brain can also be summarized by a diagram that is like the worm’s, though much more complex. Would your connectome reveal anything interesting about you?
The first thing it would reveal is that you are unique. You know this, of course, but it has been surprisingly difficult to pinpoint where, precisely, your uniqueness resides. Your connectome and mine are very different. They are not standardized like those of worms. That’s consistent with the idea that every human is unique in a way that a worm is not (no offense intended to worms!).
Differences fascinate us. When we ask how the brain works, what mostly interests us is why the brains of people work so differently. Why can’t I be more outgoing, like my extroverted friend? Why does my son find reading more difficult than his classmates do? Why is my teenage cousin starting to hear imaginary voices? Why is my mother losing her memory? Why can’t my spouse (or I) be more compassionate and understanding?
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“The best lay book on brain science I’ve ever read.”
— Wall Street Journal by Daniel Levitin, Professor, McGill University; author of This Is Your Brain on Music and The World in Six Songs.
“This is complicated stuff, and it is a testament to Dr. Seung’s remarkable clarity of exposition that the reader is swept along with his enthusiasm, as he moves from the basics of neuroscience out to the farthest regions of the hypothetical, sketching out a spectacularly illustrated giant map of the universe of man.”
— New York Times
“[A] bracing, mind-expanding report from neuroscience’s razor edge. Accessible, witty, [e]minently logical and at times poetic, Connectome establishes Seung as an important new researcher, philosopher and popularizer of brain science. It puts him on par with cosmology’s Brian Greene and the late Carl Sagan.”
— Cleveland Plain Dealer
“Seung argues intelligently and powerfully that the self lies in the totality of the brain’s wiring.”
— Nature by Christof Koch, Professor, California Institute of Technology; Chief Scientific Officer, Allen Institute for Brain Science; author of Quest for Consciousness and Consciousness: Confessions of a Romantic Reductionist
“With the first-person flavour of James Watson’s Double Helix—an account of how DNA’s structure was discovered—Connectome gives a sense of the excitement on the cutting edge of neuroscience.”
— NewScientist by Terry Sejnowski, Professor and Director, Computational Neurobiology Lab, Salk Institute; Investigator, Howard Hughes Medical Institute; Member, National Academy of Sciences and National Academy of Engineering USA.
“An elegant primer on what’s known about how the brain is organized and how it grows, wires its neurons, perceives its environment, modifies or repairs itself, and stores information. Seung is a clear, lively writer who chooses vivid examples.”
— Washington Post
“Sebastian Seung scales the heights of neuroscience and casts his brilliant eye around, describing the landscape of its past and boldly envisioning a future when we may understand our own brains and thus ourselves.”
—Kenneth Blum, Executive Director, Center for Brain Science, Harvard University
“Sebastian Seung can do it all. He’s widely recognized as a superb physicist, a whiz with computers, and a path-breaking neuroscientist. Connectome shows that he's also a terrific writer, as inspiring as he is clear and good humored.”
—Steven Strogatz, Cornell University, author of Sync: the Emerging Science of Spontaneous Order
“In Connectome, Sebastian Seung reminds us that the human brain has contemplated itself for centuries. This is an important book, full of refreshingly new science and engaging history, about the essential quest to understand ourselves.”
—Phillip A. Sharp, MIT, 1993 Nobel Prize in Physiology or Medicine
“A landmark work, gorgeously written. No other researcher has traveled as deeply into the brain forest and emerged to share its secrets.”
—David Eagleman, author of Incognito and Sum
“Connectomics is emerging as a crucial and exhilarating field of study. Sebastian Seung takes you by the hand and shows you why. Connectome is a page turner—a book that should be read by anyone who lays claim to be thinking about the nature of life.”
—Michael Gazzaniga, University of California at Santa Barbara and author of Human and The Ethical Brain
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