By Giulio Tononi
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A Universe of Consciousness
DETAIL FROM MICHELANGELO’S CREATION OF ADAM IN THE SISTINE CHAPEL. God is pictured on a background that bears more than a passing resemblance to a section of the human brain. A detailed comparison can be found in F. L. Meshberger, “An Interpretation of Michelangelo’s Creation of Adam Based on Neuroanatomy,” Journal of the American Medical Association, 264 (1990), 1837–41.
A Universe of
HOW MATTER BECOMES
GERALD M. EDELMAN
AND GIULIO TONONI
OTHER WORKS BY GERALD M. EDELMAN
The Mindful Brain: Cortical Organization and the
Group-Selective Theory of Higher Brain Function
Neural Darwinism: The Theory of Neuronal Group Selection
The Remembered Present: A Biological Theory of Consciousness
Bright Air, Brilliant Fire: On the Matter of the Mind
Copyright © 2000 by Gerald M. Edelman and Giulio Tononi.
Published by Basic Books,
A Member of the Perseus Books Group
All rights reserved. Printed in the United States of America. No part of this book may be reproduced in any manner whatsoever without written permission except in the case of brief quotations embodied in critical articles and reviews. For information, address Basic Books, 387 Park Avenue South, New York, NY 10016-8810.
Book Designed by Kris Tobiassen
FIRST PAPERBACK EDITION
A CIP catalog record of this book is available from the Library of Congress.
eBook ISBN: 9780786722587
20 19 18 17 16 15 14 13 12 11 10 9 8 7
Frontispiece: Detail from Michelangelo’s Creation of Adam
1.1 Diagram by Descartes on how the brain forms mental images
2.1 A skeleton observing a skull, an engraving by Andreas Vesalius
2.2 William James
3.1 Virgin Forest with Setting Sun by Henri Rousseau
3.2 An ambiguous figure
3.3 Drawing by a patient with left hemineglect
3.4 Shot sequence from Eisenstein’s Potemkin
4.1 Gross anatomy of the brain
4.2 Two illustrations by Ramon y Cajal
4.3 Diagram of a synapse
4.4 Three topological arrangements of brain neuroanatomy
5.1 Distributed neural processes underlying conscious experience revealed by MEG
6.1 The corpus callosum
6.2 Anna O., a patient of Sigmund Freud
6.3 Coherence of neural processes underlying consciousness
6.4 EEG patterns during epilepsy and sleep
6.5 La Notte (The Night ), by Michelangelo
7.1 Charles Darwin
7.2 Diagram of the theory of neuronal group selection
7.3 Diagram of a value system
7.4 Darwin IV tracking colored cubes
8.1 Diagram of a global mapping
8.2 Knik glacier, Alaska
9.1 Mechanisms of primary consciousness
10.1 What is connected to what in the cerebral cortex
10.2 Diagram of a computer model of cortical integration
10.3 Solving the binding problem
10.4 Diagram of functional clustering
11.1 Diagram of mutual information
11.2 Diagram of complexity
11.3 How complexity varies, depending on neuroanatomical organization
12.1 M83, a spiral galaxy, in Hydra
13.1 Color space
13.2 Qualia space
13.3 Spring model of the dynamic core
14.1 Structures and connections mediating conscious and unconscious processes
15.1 A scheme of higher-order consciousness
17.1 Diagram of a Turing machine
17.2 Counterpart, by Arcimboldo
We wish especially to thank our colleagues Ralph Greenspan, Olaf Sporns, and Chiara Cirelli for their useful suggestions and thought-provoking discussions during the writing of this book. We are also grateful to David Sington for his penetrating editorial suggestions and critical analysis. Jo Ann Miller, the executive editor of Basic Books, gave us valuable help in clarifying portions of the text. We, of course, take full responsibility for any inadvertent errors and deficiencies that may remain. Many of the ideas and most of the work described here occurred at the Neurosciences Institute, whose Fellows are dedicated to understanding how the brain gives rise to the mind.
Consciousness has been seen as both a mystery and a source of mystery. It is one of the main targets of philosophical inquiry, but only recently has it been accepted into the family of scientific objects that are worthy of experimental investigation. The reasons for this late acceptance are clear: Although all scientific theories assume consciousness and conscious sensation and perception are necessary for their application, the means to carry out scientific investigations of consciousness itself have only recently become available.
There is something special about consciousness: Conscious experience arises as a result of the workings of each individual brain. It cannot be shared under direct observation, as the physicist’s objects can be shared. Thus, studying consciousness presents us with a curious dilemma: Introspection alone is not scientifically satisfactory, and though people’s reports about their own consciousness are useful, they cannot reveal the workings of the brain underlying them. Yet, studies of the brain proper cannot, in themselves, convey what it is like to be conscious. These constraints suggest that one must take special approaches to bring consciousness into the house of science.
In this book, we do just that, and we develop ways to answer the following questions:
- How does consciousness arise as a result of particular neural processes and of the interactions among the brain, the body, and the world?
- How do these neural processes account for key properties of conscious experience? Each conscious state is unified and indivisible, yet at the same time, each person can choose among an immense number of different conscious states.
- How can we understand different subjective states—so-called qualia—in neural terms?
- How can our understanding of consciousness help connect strictly scientific descriptions to the wider domain of human knowledge and experience?
To describe the neural mechanisms that give rise to consciousness, to show how the general properties of consciousness emerge as a result of the properties of the brain as a complex system, to analyze the origins of subjective states or qualia, and to show how the successful pursuit of all these efforts may change our views of the scientific observer and of long-held philosophical positions is, of course, a tall order, and in the short compass of this volume much of interest must be omitted. But the main outlines of a solution to the problem of consciousness can be sketched by paying close attention to our four basic questions. Our answers are based on the assumption that consciousness arises within the material order of certain organisms. However, we emphatically do not identify consciousness in its full range as arising solely in the brain, since we believe that higher brain functions require interactions both with the world and with other persons.
Once we establish this new understanding of how consciousness emerges, we touch on several interesting issues that derive from this perspective. We propose a new view of the scientific observer, and we explore how we can know what we know—the realm of epistemology. Finally, we discuss the question of which subjects are appropriate for scientific study. Exposing these matters to scrutiny is important because our position—that consciousness arises as a particular kind of brain process that is both highly unified (or integrated) and highly complex (or differentiated)—has wide-ranging implications.
To untangle the bases of consciousness and account for some of its properties, we consider a number of challenging subjects. Indeed, before we get to the central issue, the neural substrate of consciousness, we review structural and functional features of brain organization, as well as certain essential aspects of brain theory. To make the task easier for the reader, we have prefaced each major part of the book with a prologue and each chapter with a brief introduction. We suggest that to obtain a synoptic view, the reader peruse in order the six prologues and the introductions to the chapters. Doing so will help keep the whole picture in mind, especially in chapters that are necessary for analyzing consciousness but are not directly concerned with it. As for the later chapters, only two (chapters 10 and 11) have explicit mathematical content. The reader who is not inclined to follow the details may get a reasonable understanding of their meaning by perusing the figures and “humming the tune.” For those who wish to pursue specific issues or references, we have placed notes at the back of the book. The notes are not, however, necessary for comprehending our argument. We hope that by the end of the journey through the text, readers will find themselves with a new view of how matter becomes imagination.
The World Knot
When I turn my gaze skyward I see the flattened dome of the sky and the sun’s brilliant disc and a hundred other visible things underneath it. What are the steps which bring this about? A pencil of light from the sun enters the eye and is focussed there on the retina. It gives rise to a change, which in turn travels to the nerve layer at the top of the brain. The whole chain of these events, from the sun to the top of my brain, is physical. Each step is an electrical reaction. But now there succeeds a change wholly unlike any that led up to it, and wholly inexplicable by us. A visual scene presents itself to the mind: I see the dome of the sky and the sun in it, and a hundred other visual things beside. In fact, I perceive a picture of the world around me.1
With this simple example, in 1940, the great neurophysiologist Charles Sherrington illustrated the problem of consciousness and his belief that it was scientifically inexplicable.
A few years earlier, Bertrand Russell used a similar example to express his skepticism about the ability of philosophers to arrive at a solution:
We suppose that a physical process starts from a visible object, travels to the eye, there changes into another physical process, causes yet another physical process in the optic nerve, and finally produces some effects in the brain, simultaneously with which we see the object from which the process started, the seeing being something “mental,” totally different in character from the physical processes, which precede and accompany it. This view is so queer that metaphysicians have invented all sorts of theories designed to substitute something less incredible.2
No matter how accurate the description of the physical processes underlying it, it is hard to conceive how the world of subjective experience—the seeing of blue and the feeling of warmth—springs out of mere physical events. And yet, in an age in which brain imaging, general anesthesia, and neurosurgery are becoming commonplace, we are aware that the world of conscious experience depends all too closely on the delicate workings of the brain. We are aware that consciousness, in all its glory, can be annihilated by a minuscule lesion or a slight chemical imbalance in certain parts of the brain. In fact, our conscious life is annihilated every time the mode of activity in our brain changes and we fall into dreamless sleep. We are also aware that our own private consciousness is, in a profound sense, all there is. The flattened dome of the sky and the hundred other visible things underneath, including the brain itself—in short, the entire world—exist, for each of us, only as part of our consciousness, and they perish with it. This enigma wrapped within a mystery of how subjective experience relates to certain objectively describable events is what Arthur Schopenhauer brilliantly called the “world knot.”3 Despite the appearance of mystery, the best hope of disentangling this knot will come from a scientific approach that combines testable theories and well-designed experiments. This book is dedicated to this end.
Consciousness: Philosophical Paradox or Scientific Object?
The subject of consciousness has not lacked for human attention. In the past, it was the exclusive domain of philosophers, but recently both psychologists and neuroscientists have begun to attack the so-called mind-body problem or, in Schopenhauer’s suggestive phrase, “the world knot.” In this chapter we briefly review classical and modern approaches to consciousness. We point out various positions taken by philosophers, psychologists, and neuroscientists, rejecting some of the more flagrant ones, such as dualism or extreme reductionism. We suggest that consciousness can be considered a scientific subject and that it is not the sole province of philosophers.
Everyone knows what consciousness is: It is what abandons you every evening when you fall asleep and reappears the next morning when you wake up. This deceptive simplicity reminds us of what William James said of attention at the turn of the century: “Everyone knows what attention is. It is the taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought.”1 More than one hundred years later, many think that neither attention nor consciousness is understood in any fundamental sense.
This lack of understanding is certainly not because of lack of attention in philosophical or scientific circles. Ever since René Descartes, few subjects have preoccupied philosophers so consistently as the riddle of consciousness. For Descartes, as for James more than two centuries later, to be conscious was synonymous with “to think”: James’s stream of thought, for example, was nothing but the stream of consciousness. The cogito ergo sum, “I think therefore I am,” which Descartes posed as the foundation of his philosophy in his Meditationes de Prima Philosophia,2 was a direct recognition of the centrality of consciousness with respect to both ontology (what is) and epistemology (what and how we know).
If taken too seriously, “I am conscious, therefore I exist” can lead to solipsism, the view that nothing exists but one’s individual consciousness, evidently not a view that can appeal to two authors who are sharing the writing of a book. More realistically (pun intended), that starting point leads to idealistic positions that emphasize mind over matter—ideas; perception; thought; or, in one word, consciousness. By taking mind as a starting point, however, idealistic philosophies must take pains to explain matter—which is not necessarily a better predicament than starting from mere matter to derive mind.
Descartes argued that there is an absolute distinction between mental and material substance. The defining characteristic of matter, he thought, is to be extended, to occupy space, and thus be susceptible to physical explanation, whereas the defining characteristic of mind is to be conscious or, in a broad sense of the term, to think. In this view, mental substance exists in the form of individual minds. In this way, Descartes inaugurated dualism, a position that is unsatisfactory scientifically but appears intuitively simple and appealing until one attempts to explain the connection between the mind and the body (see figure 1.1). Since the days of Descartes, philosophers have suggested versions of dualism or related alternatives. For example, a related theory is epiphenomenalism, which agrees with other theories in holding that mental events and physical events are different but maintains that the only true causes of mental experiences are physical events, with mind as a causally inefficacious by-product. In the words of Thomas Huxley, “consciousness would appear to be related to the mechanism of [the] body simply as a collateral product of its working, and to be as completely without any power of modifying that working as the steam whistle that accompanies the working of a locomotive engine is without influence upon its machinery.”3
In more recent times, philosophers have taken a materialistic stance, holding that the mind and consciousness are identical to the operations of the brain or, at least, to certain of these operations. Some materialistic positions go so far as to deny any ontological or epistemic validity to conscious- ness; they insist that there is literally nothing else beyond the functioning of brain circuits or, at least, that there is nothing else that needs to be explained. Several philosophers have suggested that once we understand the workings of the brain sufficiently well, the concept of consciousness will evaporate just as the concept of phlogiston (a hypothetical volatile constituent of all combustible substances that was thought to be released as a flame in combustion) evaporated when oxidation was understood. The mind-body problem is thus made to disappear by denying or explaining away the consciousness side of it. Other materialistic positions insist that although consciousness is generated by physical events in the brain, it is not reduced to them but, rather, emerges from them, just as the properties of water emerge from the chemical combination of two hydrogens and one oxygen but are not directly reducible to the properties of hydrogen or oxygen alone. Such positions come in various flavors, but, in general, they grant consciousness some residual status, at least from the point of view of explanation. Nevertheless, they insist that there is no “consciousness” substance separate from a “brain” substance.
The philosophical debate on the mind-body problem is by now extremely sophisticated and, in their variety, some current disputes rival those that flourished among post-Cartesian philosophers. As we had Spinoza’s dual-aspect theory, Malebranche’s occasionalism, Leibniz’s parallelism and his doctrine of preestablished harmony, we now have the identity theory, the central state theory, neutral monism, logical behaviorism, token physicalism and type physicalism, token epiphenomenalism and type epiphenomenalism, anomalous monism, emergent materialism, eliminative materialism, various brands of functionalism, and many others.4
FIGURE 1.1 A diagram by Descartes illustrating his ideas about how the brain forms mental images of an object. The transaction between mental substance and physical substance was supposed to take place in the pineal gland (H).
Despite the profusion of philosophical positions, it appears unlikely that philosophical arguments alone will lead to a satisfactory solution to the mind-body problem. In the words of Colin McGinn,5 a philosopher who takes an extreme position: “We have been trying for a long time to solve the mind-body problem. It has stubbornly resisted our best efforts. The mystery persists. I think the time has come to admit candidly that we cannot solve the mystery. [We still have no idea of how] the water of the physical brain is turned into the wine of consciousness.”
There is indeed a fundamental limitation on philosophical efforts to discern the origins of consciousness that arises, in part, from the presumption that the sources of conscious thought can be revealed by thinking alone. This presumption is as patently inadequate as efforts in previous times to understand cosmogony, the basis of life, and the fine structure of matter in the absence of scientific observations and experiments. In fact, philosophers have excelled not so much in proposing solutions to the problem but in pointing out just how intractable the problem is. What many philosophers are reiterating amounts to this: No matter what scientists do, the first-person and third-person perspectives of conscious individuals will not be reconciled, the explanatory gap will not be bridged, and the “hard” problem—the generation of sensations, of phenomenal or experiential states out of the buzzing of neurons—will not be solved.6
How have scientists fared in explaining the mystery? If we look at psychology, we find that the “science of the mind” always had trouble in accommodating what should be its central topic—consciousness—within an acceptable theoretical framework. The introspectionist tradition of Titchener and Külpe7 was the psychological counterpart of idealistic or phenomenological positions in philosophy; it attempted to describe consciousness viewed by the individual exclusively from the inside, hence the term introspection. Many introspectionists were psychological atomists; not unlike some present-day neurophysiologists, they postulated that consciousness was made up of elementary parts that could be catalogued (never mind that the American school came up with more than 40,000 sensations and the German school with just 12,000). By contrast, behaviorists notoriously attempted to eliminate consciousness completely from scientific discourse, a position not unlike that of some contemporary philosophers.
- On Sale
- Aug 1, 2008
- Page Count
- 416 pages
- Basic Books