On the Move: A Life

by Oliver Sacks

  Sitting next to Francis, I could see that his shaggy eyebrows had turned whiter and bushier than ever, and this deepened his sagelike appearance. But this venerable image was constantly belied by his twinkling eyes and mischievous sense of humor. Ralph was eager to tell Francis about his latest work—a new form of optical imaging which could show structures almost down to the cellular level in the living brain. It had never been possible to visualize brain structure and activity on this scale before, and it was on this “meso” scale that both Crick and Gerald Edelman, whatever their differences, now located the functional structures of the brain.

  Francis was very excited about Ralph’s new technique and his pictures, but at the same time he fired volleys of piercing questions, grilling Ralph, interrogating him, in a minute but also constructive way.

  Francis’s closest relationship, besides Odile, was clearly with Christof, his “son in science,” and it was immensely moving to see how the two men, forty or more years apart in age and so different in temperament and background, had come to respect and love one another so deeply. (Christof is romantically, almost flamboyantly physical, given to dangerous rock climbing and brilliantly colored shirts. Francis seemed almost ascetically cerebral, his thinking so unswayed by emotional biases and considerations that Christof occasionally compared him to Sherlock Holmes.) Francis spoke with great pride, a father’s pride, of Christof’s forthcoming book, The Quest for Consciousness, and then of “all the work we will do after it is published.” He outlined the dozens of investigations, years of work, which lay ahead—work especially stemming from the convergence of molecular biology with systems neuroscience. I wondered what Christof was thinking, Ralph too, for it was all too clear to us (and must have been clear to Francis) that his health was declining fast and that he himself would never be able to see more than the beginning of that vast research scheme. Francis, I felt, had no fear of death, but his acceptance of it was tinged with sadness that he would not be alive to see the wonderful, almost unimaginable, scientific achievements of the twenty-first century. The central problem of consciousness and its neurobiological basis, he was convinced, would be fully understood, “solved,” by 2030. “You will see it,” he often said to Ralph, “and you may, Oliver, if you live to my age.”

  In January of 2004, I received the last letter I would get from Francis. He had read “In the River of Consciousness.” “It reads very well,” he wrote, “though I think a better title would have been ‘Is Consciousness a River?’ since the main thrust of the piece is that it may well not be.” (I agreed with him.)

  “Do come and have lunch again,” his letter concluded.

  —

  In the mid-1950s, when I was in medical school, there seemed to be an unbridgeable gap between our neurophysiology and the actualities of how patients experienced neurological disorders. Neurology continued to follow the clinico-anatomical method set by Broca a century earlier, locating areas of damage in the brain and correlating these with symptoms; thus speech disturbances were correlated with damage to Broca’s speech area, paralysis with damage to motor areas, and so on. The brain was regarded as a collection or mosaic of little organs, each with specific functions but somehow interconnected. But there was little idea of how the brain worked as a whole. When I wrote The Man Who Mistook His Wife for a Hat in the early 1980S, my thinking was still grounded in this model, in which the nervous system was largely conceived as fixed and invariant, with “pre-dedicated” areas for every function.

  Such a model was useful, say, in locating the area of damage in someone with aphasia. But how could it explain learning and the effects of practice? How could it explain the reconstructions and revisions of memory we make throughout our lives? How could it explain the processes of adaptation, of neural plasticity? How could it explain consciousness—its richness, its wholeness, its ever-changing stream, and its many disorders? How could it explain individuality or self?

  Although huge advances were being made in the neuroscience of the 1970s and 1980s, there was, in effect, a conceptual crisis or vacuum. There was no general theory which could make sense of the rich data, the observations of a dozen different disciplines from neurology to child development, linguistics, and even psychoanalysis.

  —

  In 1986, I read a remarkable article by Israel Rosenfield in The New York Review of Books in which he discussed the revolutionary work and views of Gerald M. Edelman. Edelman was nothing if not bold. “We are at the beginning of the neuroscientific revolution,” he wrote. “At its end, we shall know how the mind works, what governs our nature, and how we know the world.”

  A few months later, along with Rosenfield, I arranged to meet the man himself, in a conference room near the Rockefeller University where Edelman had his Neurosciences Institute at the time.

  Edelman strode in, greeted us briefly, and then talked nonstop for twenty or thirty minutes, outlining his theories; neither of us dared to interrupt him. He then abruptly took his leave, and looking out the window, I could see him walking rapidly down York Avenue, looking to neither side. “That is the walk of a genius, a monomaniac,” I thought to myself. “He is like a man possessed.” I had a sense of awe and envy—how I should like such a ferocious power of concentration! But then I thought that life might not be entirely easy with such a brain; indeed, Edelman, I was to find, took no holidays, slept little, and was driven, almost bullied, by nonstop thinking; he would often phone Rosenfield in the middle of the night. Perhaps I was better off with my own, more modest endowment.

  In 1987, Edelman published Neural Darwinism, a seminal volume and the first in a series of books presenting and exploring the ramifications of a very radical idea which he called the theory of neuronal group selection, or, more evocatively, neural Darwinism. I struggled with the book, finding the writing impenetrable at times, in part because of the novelty of Edelman’s ideas and in part because of the book’s abstractness and lack of concrete examples. Darwin had said of the Origin that it was “one long argument,” but he buttressed it by innumerable examples of natural (and artificial) selection and by a gift of writing akin to that of a novelist. Neural Darwinism, in contrast, was pure argument—a single intense, intellectual brief from beginning to end. I was not the only person to have difficulties with Neural Darwinism; the density, audacity, and originality of Edelman’s work, its pushing beyond the bounds of language, were daunting.

  I annotated my copy of Neural Darwinism with clinical examples, wishing that Edelman himself, who had trained as a neurologist and psychiatrist, had done the same.

  —

  In 1988, I met Gerry again when we both made presentations at a conference on the art of memory in Florence.3 After the conference, we had dinner together. I found him very different from the monologist I had first encountered, when he had tried to compress a decade of intense thinking into a few minutes; now he was more relaxed, patient with my slowness. And the tone was one of easy conversation. Gerry was eager to learn of my experiences with patients—experiences which might be pertinent to his thinking, clinical stories which might be relevant to his theories of how the brain worked and of consciousness. He was somewhat isolated from clinical life at the Rockefeller, like Crick at the Salk, and both were hungry for clinical data.

  Our table had a paper tablecloth, and when points were obscure, we drew diagrams on it until their meaning was fully explored. By the time we had finished, I felt I understood his theory of neuronal group selection, or some of it. It seemed to illuminate a vast field of neurological and psychological knowledge, to be a plausible, testable model of perception, memory, and learning, of how through selective and interactive brain mechanisms a human being achieves consciousness and becomes a unique individual.

  —

  While Crick (and his co-workers) cracked the genetic code—a set of instructions, in general terms, for building a body—Edelman realized early that the genetic code could not specify or control the fate of every single cell in the body, that cellular d
evelopment, especially in the nervous system, was subject to all sorts of contingencies—nerve cells could die, could migrate (Edelman spoke of such migrants as “gypsies”), could connect up with each other in unpredictable ways—so that even by the time of birth the fine neural circuitry is quite different even in the brains of identical twins; they are already different individuals who respond to experience in individual ways.

  Darwin, studying the morphology of barnacles a century before Crick or Edelman, observed that no two barnacles of the same species were ever exactly the same; biological populations consisted not of identical replicas but of different and distinct individuals. It was upon such a population of variants that natural selection could act, preserving some lineages for posterity, condemning others to extinction (Edelman liked to call natural selection “a huge death machine”). Edelman conceived, almost from the start of his career, that processes analogous to natural selection might be crucial for individual organisms—especially higher animals—in the course of their lives, with life experiences serving to strengthen certain neuronal connections or constellations in the nervous system and to weaken or extinguish others.4

  Edelman thought of the basic unit of selection and change as being not a single neuron but groups of fifty to a thousand interconnected neurons; thus he called his hypothesis the theory of neuronal group selection. He saw his own work as the completion of Darwin’s task, adding selection at a cellular level within the life span of a single individual to that of natural selection over many generations.

  Clearly there are some innate biases or dispositions as part of our genetic programming; otherwise an infant would have no tendencies whatever, would not be moved to do anything, seek anything, to stay alive. These basic biases (towards, for example, food, warmth, and contact with other people) direct a creature’s first movements and strivings.

  And at an elementary physiological level, there are various sensory and motor givens, from the reflexes that automatically occur (for example, in response to pain) to certain innate mechanisms in the brain (for example, control of respiration and autonomic functions).

  But in Edelman’s view, very little else is programmed or built in. A baby turtle, on hatching, is ready to go. A human baby is not ready to go; it must create all sorts of perceptual and other categorizations and use them to make sense of the world—to make an individual, personal world of its own, and to find out how to make its way in that world. Experience and experiment are crucially important here—neural Darwinism is essentially experiential selection.

  The real functional “machinery” of the brain, for Edelman, consists of millions of neuronal groups, organized into larger units or “maps.” These maps, continually conversing in ever-changing, unimaginably complex, but always meaningful patterns, may change in minutes or seconds. One is reminded of C. S. Sherrington’s poetic evocation of the brain as “an enchanted loom,” where “millions of flashing shuttles weave a dissolving pattern, always a meaningful pattern though never an abiding one; a shifting harmony of subpatterns.”

  The creation of maps that respond selectively to certain elemental categories—for example, to movement or color in the visual world—may involve the synchronization of thousands of neuronal groups. Some mappings take place in discrete and anatomically fixed, pre-dedicated parts of the cerebral cortex, as is the case with color: color is constructed predominantly in the area called V4. But much of the cortex is plastic, pluripotent “real estate” that can serve (within limits) whatever function is needed; thus what would be auditory cortex in hearing people may be reallocated for visual purposes in congenitally deaf people, just as what is normally visual cortex may be used for other sensory functions in the congenitally blind.

  Ralph Siegel, in looking at the neural activity in monkeys doing a particular visual task, was very aware of the gulf between “micro” methods, in which electrodes are inserted into a single nerve cell to record its activity, and “macro” methods (fMRI, PET scans, etc.) which show whole areas of the brain responding. Conscious of the need for something in between, he pioneered a very original optical “meso” method that allowed him to look at dozens or hundreds of neurons as they interacted and synchronized with one another in real time. One of his findings—unexpected and baffling at first—was that neuronal constellations or maps could change in a matter of seconds as the animal learned or adapted to different sensory inputs. This was very much in accordance with Edelman’s theory of neuronal group selection, and Ralph and I spent many hours discussing the implications of his theory with each other and with Edelman himself, who, like Crick, was fascinated by Ralph’s work.

  Where perception of objects is concerned, Edelman likes to say, the world is not “labeled”; it does not come “already parsed into objects.” We must make our perceptions through our own categorizations. “Every perception is an act of creation,” as Edelman says. As we move about, our sense organs take samplings of the world, and from these, maps are created in the brain. There then occurs with experience a selective strengthening of those mappings that correspond to successful perceptions—successful in that they prove the most useful and powerful for the building of “reality.”

  Edelman speaks here of a further, integrative activity peculiar to more complex nervous systems; this he calls “reentrant signaling.” In his terms, the perception of a chair, for example, depends first on the synchronization of activated neuronal groups to form a “map,” then a further synchronization of a number of scattered mappings throughout the visual cortex—mappings relating to many different perceptual aspects of the chair (its size, its shape, its color, its “leggedness,” its relation to other sorts of chairs—armchairs, rocking chairs, baby chairs, etc.). In this way, a rich and flexible percept of “chairhood” is achieved, which allows the instant recognition of innumerable sorts of chairs as chairs. This perceptual generalization is dynamic, so it can be continually updated, and it depends on the active and incessant orchestration of countless details.

  Such correlation and synchronization of neuronal firing in widely separated areas of the brain is made possible by very rich connections between the brain’s maps—connections which are reciprocal and may contain millions of fibers. Stimuli from, say, touching a chair may affect one set of maps; stimuli from seeing it may affect another set. Reentrant signaling takes place between these sets of maps as part of the process of perceiving a chair.

  Categorization is the central task of the brain, and reentrant signaling allows the brain to categorize its own categorizations, then recategorize these, and so on. Such a process is the beginning of an enormous upward path enabling ever higher levels of thought and consciousness.

  Reentrant signaling might be likened to a sort of neural United Nations, in which dozens of voices are talking together, while including in their conversations a variety of constantly inflowing reports from the outside world, bringing them together into a larger picture as new information is correlated and new insights emerge.

  Edelman, who once planned to be a concert violinist, uses musical metaphors as well. In a BBC radio interview, he said:

  Think: if you had a hundred thousand wires randomly connecting four string quartet players and that, even though they weren’t speaking words, signals were going back and forth in all kinds of hidden ways [as you usually get them by the subtle nonverbal interactions between the players] that make the whole set of sounds a unified ensemble. That’s how the maps of the brain work by reentry.

  The players are connected. Each player, interpreting the music individually, constantly modulates and is modulated by the others. There is no final or “master” interpretation; the music is collectively created, and every performance is unique. This is Edelman’s picture of the brain, as an orchestra, an ensemble, but without a conductor, an orchestra which makes its own music.

  —

  When I walked back to my hotel after dinner with Gerry that evening, I found myself in a sort of rapture. It seemed to me that the moon over t
he Arno was the most beautiful thing I had ever seen. I had the feeling of having been liberated from decades of epistemological despair—from a world of shallow, irrelevant computer analogies into one full of rich biological meaning, one which corresponded with the reality of brain and mind. Edelman’s theory was the first truly global theory of mind and consciousness, the first biological theory of individuality and autonomy.

  I thought, “Thank God I have lived to hear this theory.” I felt as I imagined many people must have felt in 1859 when the Origin came out. The idea of natural selection was astounding but, once one thought about it, obvious. Similarly, when I grasped what Edelman was about that evening, I thought, “How extremely stupid of me not to have thought of this myself!” just as Huxley had said after reading the Origin. It all seemed so clear suddenly.

  A few weeks after my return from Florence, I had another epiphany, of a rather improbable and comic sort. I was driving up to Lake Jefferson through the lush countryside of Sullivan County, enjoying the tranquil fields and hedgerows, when I saw—a cow! But a cow transfigured by my new Edelmanian view of animal life, a cow whose brain was constantly mapping all its perceptions and movements, a cow whose inner being consisted of categorizations and mappings, neuronal groups flashing and conversing at great speed, an Edelmanian cow suffused by the miracle of primary consciousness. “What a wonderful animal!” I thought to myself. “Never have I seen a cow in this light before.”