Second Nature: Brain Science and Human Knowledge available in Hardcover
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- Yale University Press
A renowned neuroscientist explains how our brains and bodies give rise to knowledge, creativity, and mental experience
|Publisher:||Yale University Press|
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About the Author
Gerald M. Edelman, M.D., Ph.D., is director, The Neurosciences Institute; president, Neurosciences Research Foundation; and chairman, Department of Neurobiology, The Scripps Research Institute. He has received many honors and awards, including the Nobel Prize for Physiology or Medicine. He lives in La Jolla, CA.
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Second NatureBRAIN SCIENCE AND HUMAN KNOWLEDGE
By Gerald M. Edelman
YALE UNIVERSITY PRESSCopyright © 2006 Gerald M. Edelman
All right reserved.
Chapter OneThe Galilean Arc and Darwin's Program
Almost everything that distinguishes the modern world from earlier centuries is attributable to science, which achieved its most spectacular triumphs in the seventeenth century. -BERTRAND RUSSELL
The Origin of Species introduced a mode of thinking that in the end was bound to transform the logic of knowledge, and hence the treatment of morality, politics, and religion. -JOHN DEWEY
Something definite happens when to a certain brain state a certain 'sciousness corresponds. -WILLIAM JAMES
HENRY ADAMS DIDN'T KNOW the half of what was coming. But he did sense a transformation of our existence by scientific technology. We are in the midst of a revolution: communication, computers, the Internet, the explosion of travel by land and air, atomic power, biological manipulation of our genetic makeup. One could goon and on about the technological substrate and the globalization that has changed the pace of our lives, the modes of our thought, our place in nature, and our threat to it.
What has happened to our conception of nature and of our second nature? To answer this question we have to take a longer view of Western science, particularly of physics and biology. I pick two figures, Galileo Galilei and Charles Darwin, to highlight the developments that have so changed our lives.
First, Galileo, who can be taken to represent the birth in the seventeenth century of modern physics, the broadest of modern sciences. The philosopher Alfred North Whitehead, in his book Science and the Modern World, called Galileo's achievement "the quiet commencement of the most intimate change in outlook which the human race had yet encountered." Surely, we must be impressed by the arc of modern physics ranging from Galileo's ideas on the heavens and his experiments on inertia to our present cosmology and theories of matter. We must confront the weird domain of the very small described by quantum mechanics as well as the grand elegance of general relativity as it opens up vistas of the very large, the universe itself. So now the Galilean arc ranges from nuclear power to solid-state physics, to the exploration of space, and to the origin of the universe itself in the Big Bang.
Even before these advances, a vision of the basis of life, the evolution of living things, was laid down by Charles Darwin in the second half of the nineteenth century. Darwin's development of the idea of natural selection provided the theoretical basis for understanding life itself, particularly when it was coupled with Mendelian genetics in the twentieth century. The further development of molecular biology in the latter part of that century has made it possible to change the very basis of biological reproduction.
In looking over the domains of nature it may appear that, if we include Darwin, the Galilean arc has provided an enlightened understanding of all major subject categories: galaxies, stars, and planets, the structure of matter, the nature of genes and biological evolution. Henry Adams's plate today would be more than full of scientific matters covering much of our existence. But there is a gap or an incompleteness in the Galilean arc. We have not yet scientifically founded the bases of consciousness in the brain, an issue that, until recently, has been left to the philosophers.
There are reasons for this. Until recently, noninvasive methods of examining events in the brain were lacking. More than that, consciousness is a first-person affair, whereas the objective methodology of science is a third-person affair. Opinions, subjectivity, and the like cannot be admitted in scientific experiments. An equally large factor affecting the scientific approach to consciousness can be attributed to the influential thoughts of René Descartes. Sometime after Galileo, Descartes essentially removed the mind from nature. He did this by thought alone, concluding that there were two substances: res extensa, extended things that were susceptible to physics, and res cogitans, thinking things that were not extended in space and that were unavailable to physics. Descartes's dualism and its various subsequent derivations have had a profound effect on the approach to consciousness as a valid scientific target.
This state of affairs is most curious. In principle, no subject is a priori immune from scientific inquiry. Yet the very ground of our awareness has been left outside the pale! Science is imagination in the service of the verifiable truth. And as such, imagination is actually dependent on consciousness. Science itself is so dependent. As the great physicist Erwin Schrödinger observed, no scientific theory in physics includes sensations and perceptions and to get ahead it must therefore assume these phenomena as being outside of science's grasp.
Must we accept this state of affairs? Or can science complete the Galilean arc? If it cannot, must it leave the ground of consciousness to the philosophers, to the humanities, and thereby acquiesce to the divorce that so concerned Henry Adams?
Thanks to discoveries about the brain and advances in brain theory in the past twenty years, it seems we do not have to remain in this predicament. We can study consciousness even in the face of subjectivity. My aim here is to show how. But first, let us turn to the significance of a scientific understanding of consciousness.
I have found that some people do not believe that a scientific account of consciousness offers much in the way of consequences. My remarks here are not specifically aimed at these doubters, but I hope they will persuade some at least to consider the contrary position. I start with a big assumption: that we have a satisfactory scientific theory of consciousness based on brain activity. What would its significance be?
First, it would clarify the relation between mental and physical events and clear up some outstanding philosophical puzzles. We would no longer have to consider dualism, panpsychism, mysterianism, and spooky forces as worth pursuing. Time would be saved, at the least. And in clarifying these issues, we would have a better view of our place in the natural order. We would be able to corroborate Darwin's view that the human mind is the outcome of natural selection and thereby complete his program.
We would also have a better picture of the bases of human illusions, useful and otherwise. One illusion I hope to dispel is the notion that our brains are computers and that consciousness could emerge from computation. Furthermore, a successful theory of consciousness might clarify the place of values in a world of facts. In connection with both of these issues, a brain-based theory would be of great use in understanding psychiatric and neuropsychological syndromes and diseases.
Tangent to these matters, a brain-based theory might contribute to our notions of creativity. It might even provide a clearer view of the connection of objective descriptions derived from hard science to normative issues that arise in aesthetics and ethics. To that degree, it may help undo the divorce between science and the humanities.
Above all, achieving these ends may contribute to and affect the formulation of a biologically based epistemology-an account of knowledge that relates truth to opinion and belief, and thought to emotion by including aspects of brain-based subjectivity in an analysis of human knowledge.
The most remarkable outcome of a satisfactory brain theory would be the construction of a conscious artifact. Although that goal is presently in the realm of fantasy, scientists at The Neurosciences Institute in La Jolla, California, have already built brain-based devices that have perceptual and memorial capabilities. Of course, a minimum requirement for us to believe that we had constructed a conscious device would rest in its ability to report, through a language, its internal phenomenal states while we measure its neural and bodily performance. This requirement is presently far from being met. But if it were, we would have an unparalleled opportunity to explore brain, body, and environment as they interact in such a device. Would it "see" or "sense" the world in ways we cannot imagine? Only a receipt of messages from outer space would exceed this enterprise in excitement. We shall have to wait.
I propose now to provide some support for the assumption I made that we have a satisfactory theory of consciousness. I shall do so by presenting a brief account of consciousness and of the brain dynamics from which it emerges. Following that, we can return to analyze their consequences in greater detail.
Chapter TwoConsciousness, Body, and Brain
Like the entomologist in search of brightly colored butterflies, my attention hunted, in the garden of gray matter, cells with delicate and elegant forms, the mysterious butterflies of the soul. -SANTIAGO RAMÓN Y CAJAL
I HAVE WRITTEN EXTENSIVELY on the details of brain structure and dynamics as they relate to perception, memory, and consciousness. I have no intention of repeating these details here. Instead, I shall describe some of the main features of consciousness. Then I will give a brief account of brain activity in terms of a theory called Neural Darwinism. This will allow me to show how consciousness emerges from brain dynamics. I shall not hesitate to make large statements without detailed proof; such proof can be found elsewhere.
We all know implicitly what consciousness is. It is what you lose on entering a dreamless deep sleep and, less commonly, deep anesthesia or coma. And it is what you regain after emerging from these states. In the awake conscious state, you experience a unitary scene composed variably of sensory responses-sight, sound, smell, and so on-as well as images, memories, feeling tones and emotions, a sense of willing or agency, a feeling of situatedness, and other aspects of awareness. Being conscious is a unitary experience in the sense that you cannot at any time become totally aware of just one thing to the complete exclusion of others. But you can direct your attention to various aspects of a less inclusive but still unitary scene. Within a short time, that scene will vary in one degree or another and, though still integrated, will become differentiated, yielding a new scene. The extraordinary fact is that the number of such privately experienced scenes is apparently limitless. The transitions seem to be continuous, and in their complete detail they are private, first-person subjective experiences.
Conscious states are often, but not always, about things or events, a property called intentionality. But they do not necessarily always show this property; they can, for example, be about a mood. There is often a just-aware "fringe," as William James called certain barely perceived states. Conscious states can also involve the awareness of agency or the willing of an action.
The property most often described as particularly mysterious is the phenomenal aspect of consciousness, the experience of qualia. Qualia are, for example, the greenness of green and the warmness of warmth. But several students of the subject, myself included, go beyond these simple qualities and consider the whole ensemble of conscious scenes or experiences to be qualia.
Many consider explaining qualia to be the acid test of a consciousness theory. How can we explain not only qualia but all the other features of consciousness? The answer I propose is to look into how the brain works, formulating a global brain theory that can be extended to explain consciousness. Before I do so, however, one more distinction will prove useful. As human beings, we know what it is like to be conscious. Moreover, we are conscious of being conscious and can report on our experience. Although we cannot experience the consciousness of members of another species, we surmise that animals like dogs are conscious. We do this on the basis of their behavior and the close similarity of their brains to ours. But we do not usually attribute consciousness of consciousness to them.
This is the basis for a useful distinction. Dogs and other mammals, if they are aware, have primary consciousness. This is the experience of a unitary scene in a time period of at the most seconds that I call the remembered present-a bit like the illumination by a flashlight beam in a dark room. Although they are aware of ongoing events, animals with primary consciousness are not conscious of being conscious and do not have a concept of the past, the future, or a nameable self.
Such notions require the ability to experience higher-order consciousness, and this depends on having semantic or symbolic capabilities. Chimpanzees appear to have the rudiments of these capabilities. In our case, they exist in full flower because we have syntax and true language. With the ability to speak, we can free ourselves temporarily from the limitations of the remembered present. Nonetheless, at all times when higher-order consciousness is present we also possess primary consciousness.
Against this background, let us turn to the organ responsible for all these extraordinary traits: the brain. The human brain weighs about three pounds. It is one of the most complicated material objects in the known universe. Its connectivity is awe-inspiring: the wrinkled cortical mantle of the brain (figure 1, top) has about thirty billion nerve cells or neurons and one million billion connections. The number of possible active pathways of such a structure far exceeds the number of elementary particles in the known universe.
This is not the place to go into detail about how the brain gives rise to consciousness. I have done that in several books, which may be consulted. But I do want to provide a working picture of brain structure and activity. I propose to use a mixture of down-to-earth description, analogy, and metaphor-just enough to give an idea of how consciousness arises.
To start with, let's consider the fundamental cells that carry signals in the brain. These are the neurons, which have a treelike set of branches (dendrites) and usually a single extended process (the axon) that serves to connect one neuron to another. This connection, called the synapse (figure 1, bottom), is a critical element in ensuring the function of brain circuits. This is so because electricity traveling down the axon releases little packets of chemicals called neurotransmitters at the synapse. These chemicals cross the small distance inside the synapse and bind to certain receptors present often at the dendrites of the receiving cell. If the release happens often enough, the receiving or postsynaptic cell fires and can repeat the process and signal yet another cell. Imagine such a process summing up across a myriad of synapses, and you will get an idea of why with modern methods we can actually record the otherwise minute currents and potentials over the scalp. Neurophysiologists can in fact record more precisely from single cells by invading the brain and inserting microscopic electrodes within individual neurons.
A key property of synapses is that they are plastic: various activities and biochemical events can change their strength. These changes can in turn determine which neuronal pathways are selected to transmit signals. Patterns of such changes in synaptic strength provide a basis for memory. At this point, it may be useful to mention that synapses come in two flavors: excitatory and inhibitory. Both can exhibit plasticity; together they help select the functioning signal pathways of the brain.
Excerpted from Second Nature by Gerald M. Edelman Copyright © 2006 by Gerald M. Edelman. Excerpted by permission.
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Table of Contents
one The Galilean Arc and Darwin's Program....................5
two Consciousness, Body, and Brain....................12
three Selectionism A Prerequisite for Consciousness....................23
four From Brain Activity to Consciousness....................35
five Epistemology and Its Discontents....................43
six A Brain-Based Approach....................53
seven Forms of Knowledge The Divorce between Science and the Humanities....................68
eight Repairing the Rift....................76
nine Causation, Illusions, and Values....................88
ten Creativity The Play between Specificity and Range....................98
eleven Abnormal States....................106
twelve Brain-Based Devices Toward a Conscious Artifact....................125
thirteen Second Nature The Transformation of Knowledge....................142
A conversation with Dr. Gerald M. Edelman
Q: Is there a single message in Second Nature you want to convey?
A: We are about to understand how consciousness arises in the workings of the brain. I argue that while the scientific picture of the world describes the bases for all phenomena including consciousness, there remain arenas, such as ethics and aesthetics, which cannot be fully described by a scientific approach.
Q: What are the most significant advances in brain science that you address in this book?
A: We now understand that the brain is not organized like a computer. A better image is provided by considering it to be a biological system whose form and activity involve pattern recognition rather than logic. This implies that each person’s brain is unique in the history of the universe.
Q: Will we ever understand how consciousness arises as a result of brain action?
Yes, we will. We are on the brink of understanding how consciousness arises as a result of myriad mutual interactions of nerve cells distributed in our cerebral cortex. Integration of these interactions allows us to make enormous numbers of distinctions that are the hallmark of consciousness. Indeed, someday we may be able to make a conscious artifact.
A: Will knowledge and how we acquire it be reduced completely to a scientific description?
No. This is a major point of the book. For example, each brain has a developmental and evolutionary history that is largely irreversible and uniquely individual. Furthermore, creative thought, scientific and otherwise, starts with ambiguity, and only in some instances can it proceed to scientific clarity.