Brain Architecture: Understanding the Basic Plan (Medicine)

282 Pages·2002·14.54 MB·English

by  Larry W. Swanson

BRAIN ARCHITECTURE
THREE MAMMALIAN BRAINS
These drawings show the appearance of the brain in three large mammals: human,
dolphin, and elephant. In each case the brain has been cut into right and left halves,
and a midline view of the right half is presented. In the dolphin and elephant brains, th
brainstem and cerebellum have been removed for clarity. The brains are drawn to scale.
From F. Leuret and P. Gratiolet. Anatomic comparee du systeme nerveux
(Bailliere: Paris, 1857).
BRAIN ARCHITECTURE
Understanding the Basic Plan
LARRY W. SWANS ON
Milo Don and Lucille Appleman Professor of Biological Sciences
University of Southern California

OXFORD
UNIVERSITY PRESS
2003
Oxford University Press
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Library of Congress Cataloging-in-Publication Data
Swanson, Larry W.
Brain architecture : understanding the basic plan / Larry W. Swanson.
p. cm.
Includes bibliographical references and index.
ISBN 0-19-510504-4 (cloth)—ISBN 0-19-510505-2 (pbk.)
1. Brain. 2. Neural circuitry. 3. Neuroanatomy. I. Title.
QP376.S86 2003
573.8'6—dc21
2002022015

9876543
Printed in the United States of America
on acid-free paper
From what has been said, I shall draw the only conclusion which legitimately
results; namely, that the mechanism of thought is unknown to us—a conclusion
with which every one will probably agree. None the less the fundamental ques-
tion I have suggested exists: for what concerns us is to know whether our present
ignorance on this subject is a relative ignorance which will vanish with the progress
of science, or an absolute ignorance in the sense of its relating to a vital problem
which must forever remain beyond the ken of physiology. For myself, I reject the
latter opinion, because I deny that scientific truth can thus be divided into frac-
tions. How, indeed, can one understand that it is permitted to the physiologist to
succeed in explaining the phenomena that occur in all the organs of the body, ex-
cept apart of those that occur in the brain? Such distinctions cannot exist among
vital phenomena. Unquestionably they present very different degrees of complex-
ity, but they are all alike in being either soluble or insoluble by our examination;
and the brain, marvelous as those metaphysical manifestations that take place in
it appear to us, cannot form an exception among the other bodily organs.
—CLAUDE BERNARD (1873)
To extend our understanding of neural Junction to the most complex human phys-
iological and psychological activities, it is essential that we first generate a clear
and accurate view of the structure of the relevant centers, and of the human brain
itself, so that the basic plan—the overview—can be grasped in the blink of an

eye.
—SANTIAGO RAMON T CAJAL (1909)
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NOTE TO THE READER
There are many ways to think about how the brain works, from
philosophy and mathematical models at one end of the spec-
trum, to psychology, to biology, to chemistry and physics at the other
end. Yet one thing remains common to all of them—the physical
brain itself. For over 2500 years scientists have been researching the
architecture, structural organization, or anatomy of the brain as an
organ, the all-important organ of mind. This book is an attempt to
distill the general principles that have stood the test of time, to pres-
ent a new model of how the brain's functional systems are organ-
ized, and to point out how much remains to be learned about what
is far and away the most complex yet intrinsically interesting object
that we know of. It is written for anyone—whether computer scien-
tist, physicist, psychologist, biologist, or general reader—interested
in learning more about the basic architecture of the brain. I have
taken an historical approach to give a flavor for how this problem
has been approached down through the ages. It has been an excit-
ing, heroic effort that is far from over, and it is important to appre-

ciate that a mixture of experimental and theoretical approaches has
been used from the beginning. History has shown that structure and
function are simply two sides of the same coin, inexorably inter-
twined—both necessary and both dependent on the other.
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PREFACE
No great discovery is the work of one man, or even one generation, but may rep-
resent centuries of human endeavour.
—CHARLES SINGER (1957)
A s a new graduate student in the laboratories of the psychiatry de-
JL\partment at Washington University (St. Louis), I was deeply im-
pressed with the voracious eating behavior that is triggered when a spe-
cific neurotransmitter molecule like noradrenaline is microinjected
directly into a tiny, very specific region of the brain—and with the equally
striking drinking behavior that immediately follows the microinjection
of different neurotransmitters like acetylcholine or angiotensin. What
neural circuits do these chemicals activate to create sensations of hunger
and thirst, appetites for food and water, and searching for these very
specific goals? Later on, as a postdoctoral fellow in the anatomy and bi-
ology departments, I began to search for and analyze the hazily under-
stood brain systems that underlie these and other types of motivated and
emotional behaviors, and this interest has guided my research and think-
ing ever since. Twenty-five years later, at least one thing seems obvious:
the explanation of an y motivated behavior like eating, drinking, de-
fending one's territory, reproducing and caring for offspring, or even
sleeping—in terms of an interacting set of underlying neural systems
with distinct functions—really amounts to explaining how the entire
nervous system is arranged and works as a whole.
For example, a specific behavioral response like eating can be ac-
tivated in many different ways (hunger, advertising, habit, and so on),
goal objects need to be searched out effectively and dealt with ap-
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