The purpose of this book is to answer, in simple language, two questions: what the brain does and how it does it. The brain is one of the most fascinating objects in the universe, a few pounds of squishy matter that builds our mental world. Thus, if we understood the brain, we would understand our minds, who we are, the center of our human experience. As humans, we are defined by our minds and we have struggled to understand ourselves, attempted to do throughout our history as a species. This struggle has culminated in efforts to understand how the brain functions. For these reasons, many scientists—myself included— think that neuroscience is the most fascinating topic to which you can devote your life.
But despite our efforts, we still don’t have a general theory that explains how the brain works or generates our mind. This is likely due to methodological limitations. Neuroscientists have traditionally tried to decipher the function of the brain by studying how neurons work using methods to record the activity of individual neurons, taking the brain apart one neuron at a time to put it all together at the end. But the human brain has close to 100 billion neurons, and, lacking methods to measure the activity of many neurons operating at the same time, we have been missing the bigger picture, how neurons interact as a group. Studying individual neurons one by one makes it impossible to reveal the brain’s function, the same way that looking at individual pixels on a TV screen will never enable us to see images and understand the function of the TV or the meaning of the movie playing on it. In my view, neurons acting together are like the pixels that form a particular image by turning on at the same time. These
That viewpoint is my focus in this book: that ensembles of neurons form the building blocks of brain function and that the brain uses these groups of neurons acting together to build “emergent” functional properties. Emergent properties, like magnetism, are properties of systems of many units (atoms in the case of magnetism) that are absent from the individual units themselves. Thus, by definition, these properties cannot be understood by investigating individual elements one at a time; they appear only when elements interact. In fact, one could argue that the brain is the mother of all emergent systems as it is built with an astronomical number of neurons connected by an even larger number of connections. If you wanted to build a system to generate emergent properties, you couldn’t do better than invent the human brain.
The study of emergent properties is at the frontier of science, as interactions between units in complex systems are difficult to capture experimentally or mathematically. Nevertheless, emergent properties are all around us. They dominate our world, from subatomic particles building atomic properties, to atomic interactions building molecular properties, to molecules building chemical properties of matter, to chemical properties building biological structures, to biological structures building living matter and mental activities. Nature is a ladder of emergent properties.
This book will focus on one particular emergent level, that of “neural circuits”; that is, groups of connected neurons. To me, understanding how the brain works means understanding how neural circuits carry out computations and mental processes. You could argue that how neuronal activity is transformed into thought is the key question in neuroscience. And we are aiming for that heart of the matter here. By concentrating on neural circuits, this book goes against the grain of many neuroscience textbooks that for the last two decades have focused, with increasing reductionism and exquisite detail, on molecular and cellular neuroscience. There are also textbooks that analyze the output of the brain at a behavioral, ethological, or psychological level. But the argument I make is that the heart of brain function lies in the middle of the ladder, at the
x Preface groups of neurons, or “ensembles,” are the functional unit of the brain, the images of our “brain TV.”
My intuition tells me that the critical insights lie inside the box, in the middle of the apparently complicated neural circuits formed by myriad neurons and their connections, the “impenetrable jungles where many investigators have lost themselves,” as Santiago Ramón y Cajal, whose beautiful drawings and work have inspired neuroscientists like me for over a century, sternly warned us. But in contrast to Cajal’s opinion that brain circuits are impenetrable, my argument—in line with that of many previous investigators, such as Thomas Graham Brown, Rafael Lorente de Nó, Donald Hebb, Rodolfo Llinás, John Hopfield, Valentino Braitenberg, and Moshe Abeles, among others—is that groups of neurons acting together are basic modules that simplify our understanding of brain function. To understand the jungle, we need to look at it not tree by tree but from above, and observe how groups of trees make up the forest.
This book arose from class notes and blackboard sketches for my undergraduate course, Neurobiology II: Development and Systems Neuroscience, which I have taught at Columbia University since 1996. Year after year, I have struggled to present a coherent picture of how the brain works to groups of fresh, smart, and sharp-minded undergraduate and graduate students. After many years of using textbooks that keep getting longer and heavier and bury us in a molecular tsunami of exquisite but ever more complex details, I thought it was time to step up to the plate, try to go back to the basic principles, and have a go at writing a textbook with a synthetic angle. So here it is.
This book therefore is based on my Columbia University lectures and is meant for newcomers to neuroscience. It should be accessible to laypeople, as it was written for undergraduate students with no previous background in neuroscience. It is not a comprehensive review but a personal synthesis of the field. In eighteen lectures, I will touch on examples to
Preface xi circuit level, connecting neuronal activity to thoughts via neuronal ensembles. Molecules and cells are, of course, critically important, but I don’t think they will reveal the basic principles of how the brain works. And going from behavior to understanding how the brain works, though it can reveal key mental computations, risks treating the brain as a black box, which may prevent understanding of the basic principles of its function.
review and extract basic principles. For those interested in a deeper dive into details or comprehensive treatment of molecular, cellular, behavioral, or computational neuroscience, I recommend the excellent textbooks already published, which are phenomenal pieces of work and scholarship. My goal here is not to compete with them and add yet another textbook to this long list of excellent volumes. Rather, I aim to bring back the essence of brain function using a neural circuits framework to reduce and synthesize important information from the larger textbooks into a short, succinct text you can carry in your pocket. My mission is to capture the excitement that brought me to neuroscience in the first place.
I have one caveat for this journey of ours: by design, to make a succinct synthesis, I must leave out a lot of details. The goal is to present a clear picture, and for the purpose of this introductory text, I value simplicity and clarity at the expense of detail and exhaustiveness. Let’s not get lost in that jungle. I want to be didactic and review a few examples as threads in a story, repeating key concepts on purpose. Also, instead of complex illustrations, simple drawings sketch the essence of an idea. I am reminded of a comment from my mentor, Sydney Brenner. He said, with a mischievous smile, that when you’re trying to understand something, you can choose to ignore some facts that may get in the way, as they will eventually be explained sooner or later.
Also, while I cover many parts of the brain, the thrust of the argument I will lay out has to do with the cerebral cortex, which is my area of expertise. The cortex (meaning “bark” in Latin) is a thin sheet of tissue, about 2 mm thick and a meter square in area, that covers the top of our brain. The cortex is the largest part of the nervous system in mammals and is important because it generates all our mental and cognitive abilities. Our extraordinary cognition is possible because of its huge size; it is much larger, in proportion to our body size, than that of any other animal. The cortex is the reason I am interested in neuroscience. We need to understand all of the brain, but the cortex is where it’s at for me.
The book would not have been possible without the help of many people. Gil Costa, a neuroscientist and artist, illustrated every concept with beautiful figures and provided artistic and scientific feedback.
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Lisa Hamm piloted the art design with aplomb and gusto, while Miranda Martin skillfully edited the book and shepherded us all to the finish line. My former undergraduate student Polina Porotskaya transcribed many of the lectures and also sketched initial versions of many illustrations. Jay Walkers, another former student, helped transcribe the motor system lectures. And Ricardo Martínez Murillo, Director of the Cajal Institute, provided access and permission to reprint the beautiful drawings of the master.
I also acknowledge my friend Sebastian Seung for cowriting a previous piece that I used for inspiration for the neural network lecture. Also, heartfelt thanks to my colleagues at DIPC in San Sebastian for their comments, and to my dear colleague Pat Kitcher, who shared her passion about Kant, fueling mine. Most important, Columbia University and particularly its Department of Biological Sciences provided a supportive, warm, and exciting home from which to work, think, and teach. But I am most thankful for twenty-six (and counting!) generations of undergraduate and graduate students who, with their questions, insights, and fresh spirits, sculpted my thinking and lectures over the years. And finally, to my family—the etxekoak (the people from the house, as they say in Basque)—whose love, patience, and support has provided me the roots from which to grow.
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The acclaimed neuroscientist Rafael Yuste provides a conversational and accessible introduction to the brain. Beginning from basic elements of neuroscience, he guides readers through increasingly sophisticated topics, developing a unified framework for how the brain functions. The book describes how the brain is organized and how it develops, how neurons operate and form neural circuits, and how these circuits function as neural networks to generate behavior and mental states. Yuste challenges the traditional view that the brain is an input-output machine that reacts reflexively to sensory stimuli. Instead, he argues, the purpose of the brain is to make a predictive model of the world in order to anticipate the future and choose successful courses of action. Readers gain insight into the workings of sensory and motor systems and the neurobiological basis of our perceptions, thoughts, emotions, memories, and consciousness. Peppered with anecdotes and illustrated with elegant drawings and diagrams, this succinct and cohesive book is accessible to readers without previous background in the subject. It is written for anyone seeking to grasp the core principles of neuroscience or looking for a fresh and clear perspective on how the brain works.
“Lectures in Neuroscience aptly conveys the excitement of a field of research that is continually opening up new vistas. Yuste’s style is easygoing, conversational, and often witty.”
RALPH GREENSPAN , associate director, Kavli Institute for Brain and Mind, UC San Diego
“Rafael Yuste, a leading neuroscientist and early advocate of the BRAIN Initiative, presents his stimulating view of the fundamental organization of the brain: circuits that convert predictions into actions. Focusing on the mammalian cerebral cortex and emphasizing repeating patterns across sensory perception, action, and cognition, Yuste is enthusiastic, conversational, and opinionated. It’s a book I wish I had read when making the transition from molecular genetics to neuroscience.”
CORI BARGMANN , Torsten N. Wiesel Professor, The Rockefeller University
RAFAEL YUSTE is professor of biological sciences and director of the NeuroTechnology Center at Columbia University. An expert on the function of the cerebral cortex, he also advocates for human rights protection of brain activity. Yuste is the chair of the NeuroRights Foundation and helped initiate the U.S. BRAIN Initiative and the International Brain Initiative.
COVER IMAGE : Neuronal circuits in human cerebral cortex. Courtesy of the Cajal Institute, “Cajal Legacy,” Spanish National Research Council (CSIC), Madrid, Spain.
COVER DESIGN : Lisa Hamm
ISBN: 978-0-231-18646-9