Tales from Both Sides of the Brain : A Life in Neuroscience (9780062228819)

by Gazzaniga, Michael S.

  Discovering that a simple surgical intervention could produce two mental systems, each with its own sense of purpose and quite independent of the other, was the first shocker back in 1960. Gradually realizing that mind left and mind right were each aggregators of still other mental systems, dozens, if not thousands of them, focused our attention on how these systems interact. Do the separate systems have to be physically connected like bulbs on a string of Christmas lights or can they signal one another to act through other information channels? For instance, when a tree limb adds branches, the limb does not send a signal to the cells at the crotch of the tree to add more cells for support. The added physical weight of the new branches is detected locally by the cells at the crotch, and they automatically respond by making more cells to beef up the support. There is not a direct, privileged, discrete signal to add more cells. This process can only be understood by considering the whole physical reality of a tree. Likewise in the brain, there are many cueing systems other than neuron-to-neuron communication, from the ever-present oscillations of brain activity to local metabolic cueing systems. The interaction of discrete brain systems must involve all of these mechanisms and more.

  Adding to our understanding of why the brain seems undisturbed by disconnections was not only the notion that it was, in a sense, sending half its decisions into the realm of the unconscious; it was also the discovery of the “interpreter.” This special left brain system kept note of all the behaviors that resulted from the many mental systems. It appeared to be the surveillance camera on our behavior, which, of course, was the evidence that a mental or cognitive act had occurred. The interpreter not only took note; it tried to make “sense” out of the behavior by keeping a running narrative going on about why a string of behaviors was occurring. It is a precious device and most likely uniquely human. It is working in us all the time as we try to explain why we like something or have a particular opinion, or rationalize something we have done. It is the interpreter device that takes the inputs from the massively modularized and automatic brain of ours and creates order from chaos. It comes up with the “makes sense” explanation that leads us to believe in a certain form of essentialism, that is, that we are a unified conscious agent. Nice try, interpreter!

  As I look back on my story, I realize I too have been conditioned by my trade to desire an ending, a summing up of my research. After sitting and listening to thousands of seminars over the years, I am all too familiar with the sentiment, “Does this guy know there is supposed to be a beginning, a middle, and an end?” The individual experimental science program is supposed to have such a structure, even though there are legions of scientists who don’t seem to know how to present it that way. We live in the era of the “bottom line” mentality, with TED talks, sound bites, and news summaries. There is so much information to digest, we can only hope to grasp the world with compact and seemingly complete stories. We don’t want to be left dangling.

  We are all suckers for this information diet, and we all have come to depend on it, just like we have all succumbed to the instant gratification of texting and cell phones. And yet what separates the dilettante from the sophisticate is the appreciation that everything is not simple. The trick seems to be able to talk clearly while remaining fully aware of the underlying complexity of any story. For me it is the overwhelming realization that when trying to figure out how the brain does its masterful trick of enabling minds, we are barely at the starting line. Dig as deep as you want into human history: As long as there is a written record of thought, there is a record of humans wondering about the nature of life. It becomes obvious that all of us are just hopping into an ongoing conversation, not structuring one with a beginning, a middle, and an end. Humans may have discovered some of the constraints on the thought processes, but we have not yet been able to tell the full story.

  ACKNOWLEDGMENTS

  First and foremost, I would like to close with a toast to all of our “split-brain” participants. Without their generosity, dedication, long hours, and endless patience we would never have learned as much as we have about the brain’s structure and function. All of them worked hard, and all of us enjoyed our time together over these many years.

  Second, the dozens of scientists that have participated in not only the studies reported in this book, but also the many other studies carried out over the past fifty years, deserve my deepest gratitude. Many were graduate students, postdoctoral students, faculty, and visitors from other institutions. All of them were as captivated as I was by the patients and their devotion to the research enterprise. They did great work.

  In preparing this book I want to offer special thanks to several colleagues who read it in full and offered many helpful suggestions. I will list them alphabetically: Floyd Bloom, Leo Chalupa, Scott Grafton, Steven Hillyard, Michael Posner, Marc Raichle, and John Tooby. I also want to thank my wife, Charlotte; my sister Rebecca; and my good friends Dan Shapiro and Eric Kaplan—all offered extensive suggestions and edits. Finally, I could not carry out these assignments without the help of Jane Nevins at the Dana Foundation.

  My steadfast agent, John Brockman, has always supported my efforts. He sticks with his people and keeps our eyes focused on the goals of scientific writing for the general public. For the past years, I have been fortunate to be with Dan Halpern at Ecco, HarperCollins. Dan spotted something in my little book on ethics and has been my publisher ever since. Thanks also go to Kallie Hill, my undergraduate research assistant who helped tremendously with the videos and the referencing. Lastly, my thanks to Hilary Redmon, my editor. She wrestled this wandering manuscript into coherence and always with a smile. I am in her debt.

  APPENDIX I

  1981 NOBEL PRIZE FOR PHYSIOLOGY OR MEDICINE1

  Adapted from an article previously published in Science, October 30, 1981.

  The 1981 Nobel Prize for Physiology or Medicine was awarded to three American-based scientists. Half of the prize went to Roger W. Sperry at the California Institute of Technology; the other half was awarded jointly to David H. Hubel and Torsten N. Wiesel of Harvard University.

  Upon hearing the first news bulletin that Roger Wolcott Sperry, Ph.D., had been awarded the 1981 Nobel Prize for Physiology or Medicine, his colleagues and students could ask only the question, “Which aspect of his work was being rewarded?” Prior to actually knowing, there were at least three major areas of research that seemed deserving—developmental neurobiology, experimental psychobiology, and human split-brain studies. It was, of course, the final body of work that was honored, but disciples of the other studies remain convinced that the other approaches were just as deserving.

  The Nobel award to Sperry, professor of psychobiology in the Division of Biology at the California Institute of Technology, serves as an inspiration to those who believe that understanding the human conscious process is the ultimate objective of neuroscience and that it can be studied with scientific rigor. It represents a grand appreciation of Roger W. Sperry for his relentless pursuit of an understanding of the conscious processes of the human brain, a pursuit he began with related but more fundamental studies more than forty years ago and maintained with a singular excellence and passionate energy. In fact, it can be said that it is Roger Sperry’s overall body of work that has served to conceptualize the objectives and questions pursued in much of current neuroscience.

  The particular studies of the human brain cited in the Nobel award began in the early 1960s, and the application of the initial insight gained from these split-brain studies to subsequent brain research has all the earmarks of a Sperry enterprise. It all started in 1961 when Joseph E. Bogen, M.D., proposed split-brain surgery be carried out on a forty-eight-year-old war veteran in an effort to control otherwise intractable epilepsy. Bogen was aware of Sperry’s earlier work on severing the connections between the hemispheres in animals, and Sperry and Ronald E. Myers had already demonstrated striking disconnection effects, that is, that information learned by one half brain did not transfer to the
other. At the time of the human studies, the animal paradigm was already in pervasive use in experimental laboratories around the world.

  In fact, the animal work done by Sperry stood in dramatic contrast to prior human work on callosum-sectioned patients that had been carried out in the early 1940s. These early reports suggested that cutting the forebrain commissures, as they are called, had no detectable effect on interhemispheric communication. It was these studies, in part, that discouraged the view that discrete pathways in the brain carried specific kinds of information. There was some question about the usefulness of the surgical technique as well for controlling epilepsy, but Bogen, after a careful review of the medical cases, concluded there was a good chance the surgery should help. That proved correct. In this new light, the stage was also set for new experimental observations on split-brain humans—a task made possible over the years by the generous cooperation of the patients themselves.

  No one was prepared for the riveting experience of observing a split-brain patient generating integrated activities with the mute right hemisphere that the language-dominant left hemisphere was unable to describe or comprehend. That was the sweetest afternoon. It was clear that the animal model held for humans, and, as a result, Sperry masterminded a program of human split-brain research that continues today. The implications of these findings for theories of consciousness and cerebral specialization, for cognitive science and clinical neurology, and even for thoughts about human values were all developed in Sperry’s laboratory. He was exceedingly generous to a series of students who went through Caltech, including Colwyn Trevarthen, Jerre Levy, Robert Nebes, Charles Hamilton, Eran Zaidel, and myself, all of whom assisted in developing the split-brain story. Yet the overall achievement was Roger Sperry’s. He is constitutionally able to be interested in only critical issues, and he drove this herd of young scientists to consider nothing but the big questions.

  There were two main phases of the human work in Sperry’s laboratory. The first was to characterize the basic neurologic and psychologic consequences of split-brain surgery and to identify the individual psychological nature of each separated hemisphere. Results accumulated over a period of six years demonstrated that the cortical commissures were critical to the interhemispheric integration of perceptual and motor functions. These studies also revealed that the mute right hemisphere was specialized for certain functions that dealt with nonverbal processes, while, not surprisingly, the left hemisphere was dominant for language. For the first time in the history of brain science, the specialized functions of each hemisphere could be positively demonstrated as a function of which hemisphere was asked to respond. The important clinical observation of brain-damaged patients had only been able to show absence of function—not the concurrent but separate and lateralized coexistence of such functions. Finally, the implications for a theory of mind were abundantly clear after observing the patient’s lack of awareness in one half brain about the activities of the other.

  The second phase of study emphasized the different cognitive styles of the hemispheres and the special linguistic capacities of the right half brain. These findings were pursued, not only by Sperry but also by other researchers investigating the lateralization story, and have included observations of both neurologically damaged and normal populations. All of this has given rise to a wealth of possibilities concerning the nature of human brain organization. The issues raised are of great interest, and pursuit of hard answers to questions central to this work comprises much of the contemporary research in neuropsychology.

  It has to be kept in mind that this body of work was preceded by a series of studies by Roger Sperry that laid the groundwork for much of the present-day field of developmental neurobiology—the experiments of which probably consume about half of all activities of neuroscientists. It all began at the University of Chicago in the 1940s. Graduate student Sperry challenged the neurobiologic theory of his brilliant mentor, Paul Weiss, that “function precedes form,” that is, that the central nervous system and its peripheral connections were not specified by genetic mechanisms. In a series of experiments that extended over twenty years, each more spectacular than the last, Sperry developed his theory of chemospecificity. His conception that chemical gradients are critical to the specification of cell-to-cell connections is still at the center of current neurobiological work, and every modern-day developmental neuroscientist is trying to find the loophole.

  After Chicago, Sperry went to Yerkes Laboratory and spent some important time with Karl Lashley. Once again Sperry intuitively rejected the going model of cerebral function and challenged Lashley’s theories on equipotentiality and mass action. While carrying out new studies, which to some extent led to the animal discoveries in split-brain work, he also put to rest a few theories Gestalt psychologists had about brain mechanisms and perceptual processes. In the early 1950s, Sperry, already recognized as a world leader in brain research, was invited to be the Hixon Professor of Psychobiology at Caltech by Nobel Laureate George W. Beadle. It was a prime job in a glorious institution, and Sperry settled in and started his major systematic work with both animals and humans in split-brain research.

  Life in science today is not as much fun as it used to be. It is full of time-consuming, boring administrative chores, of bureaucratic double talk, of responding to endless mediocre demands for “programmatic applications” in science pursuits and grant writing, and all the rest. As the dollars allocated for science decrease in number, as they have done for the last fifteen years, the request for articulated trivia goes up, and some people are actually beginning to think that this is science. We all know this, and every time I have to deal with it, I think of Sperry. He was unable to be scientifically trivial. He scowled when people proposed an extensive series of experiments. He knew how science really works, how things just happen, and that leads then are actively pursued, and pursued with vigor. He never played the bureaucratic game; he never gave in to the forces of trivia, and I hope his steadfast ways with their now grand rewards will signal the larger community to set things straight once again. Those were happy days working in his lab, trying to keep up with the intellectual excitement and freedom he always so brilliantly engendered.

  Sperry’s dazzling career had its origins in a time when brain scientists, then not so chic, studied the brain because they were interested in how its workings explained behavior. In some sense they were not interested in the brain per se, as are so many current-day neuroscientists. Their experiments constantly focused on discerning something about how the biologic system worked to support behavior, and ultimately the generation of conscious awareness. Roger W. Sperry, even while studying individual neurospecificity, saw and talked about its implications for the broader problems of nature versus nurture, a theme also so eloquently investigated by fellow award winners David Hubel and Torsten Wiesel.

  Another example of his functional approach was Sperry’s brilliant paper on how certain aspects of fish behavior changed after selective surgical manipulation, which generated an “efferent copy theory,” a theory that is central in most perceptual-motor research today. There were also those classic theoretical papers of the 1950s on “the neural basis of the conditioned response” and “neurology and the mind-brain problem.” In short, Roger Sperry was a neuroscientist who was perfectly clear about why he chose to study the brain. He worked to help elucidate the biological and psychological nature of man, a problem by no means solved, but a problem he helped define and advance knowledge about like no other scientist in the history of the world.

  THE EDITOR OF SCIENCE magazine and Roger Sperry and Joe Bogen were all pleased and generously responded to this Science article with exceedingly kind notes:

  October 21, 1981

  From Science:

  Dear Dr. Gazzaniga:

  Your sketch describing the contributions and experimental approach of Professor Sperry was elegant and informative. The descriptions of the creative atmosphere that pervaded the laboratory will evoke resonanc
e in others who have been privileged to feel the excitement of science at the frontier. I am sure that our elite readership will sense the magic that you have sought to convey. We very much appreciate your willingness to provide the material quickly. . . .

  Yours sincerely

  Philip H. Abelson

  Editor

  October 29, 1981

  California Institute of Technology

  Dear Mike:

  Have just read your article in Science and hasten to extend my deepest gratitude. You rose magnificently to the occasion overriding our personal differences with a statement that I hope and believe will always stand as a lasting credit to yourself and the rest of us involved. Of course, I feel you exaggerated my role in the split-brain developments but trust this is something most readers will quickly sense anyhow. Again, I owe you.

  Thanks also for your very nice wire and all the best.

  Sincerely,

  Roger

  October 30, 1981

  New Hope Pain Center

  (handwritten)

  Dear Mike:

  I wanted to write to express my appreciation for your appreciation (in Science 30 Oct p 517) of Roger, not only for your generous references to me and to others, but also for the super way in which you used this opportunity to make some very important points.

  Altho’ Roger may not say much (has he ever?), I’ve no doubt that he wanted very much to have said the things you said so well.

  Joe

  APPENDIX II

  I asked George Miller, “Just what is it that cognitive science wants to know?” The following week, the guiding ideas behind cognitive neuroscience took form in a long memo he wrote to me, which I present in edited form: