Download - PM Michaell Gazzaniga the Social Brain
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O t h e r B o o k s
by
M i c h a e l
S.
G a z z a n i g a
THE BISECTED BRAIN ( 1 9 7 0 )
F U N D A M E N T A L S
OF
PSYCHOLOGY ( 1 9 7 3 )
T H E IN T E G R A T E D M I N D , with Joseph LeDoux
( 1 9 7 8 )
PSYCHOLOGY ( 1 9 8 0 )
F U N D A M E N T A L S OF NEUROSCIENCE,
with Bruce T. Volpe and Diana Steen
( 1 9 8 0 )
T H E
S O C I A L
B R A I N
Discovering
th
Networks
of th Mind
MICHAEL S. GAZZANIGA
B a s i c B o o k s , Inc., P u b l i s h e r s
N e w Y o r k
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"Hymn to Zeus" from George Boas, The History of Ideas. Copyright 1969
Charles Scribner's Sons. Reprinted with permission of Charles Scribner's Sons.
Library of Congress Cataloging-in-Publication Data
Gazzaniga, Michael S.
The social brain.
Includes index.
1. BrainL ocalization of functions. 2. Split
brain. 3. Belief and doubt. 4. Neurops ychology.
I. Title. [DNLM : 1. Brainph ysiologypopular
works. 2. N europsych ologyp opular works. 3 . Social
Valuespopular works. WL 103 G289 s]
QP385.G394 1985 612' .825 85-475 63
ISBN 0^ 65-0 78 50- 8 (c loth)
ISBN 0-465-07851-6 (paper)
Copyright 1985 by Basic Books, Inc.
Printed in the United States of America
Designed by Vincent Torre
87 88 89 90 M PC 9 8 7 6 5 4 3 2 1
T o t h e m e m o r y o f J e ff r ey D a v i d H o l t z m a n
S c i e n t i st , F r i e n d , C o m p a n i o n
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CONTENTS
P R E F A C E i x
C H A P T E R 1 . T h e I n t e r p r e ti v e B r a i n 3
C H A P T E R 2 . B a s i c B r a i n P r i n c i p l e s 9
C H A P T E R 3 . S p l i t -B r a i n S t u d i e s : T h e E a r ly 2 7
Y e a r s
C H A P T E R 4 . L e f t - B r a in , R i g h t - B r a i n M a n i a : 4 7
A D e b u n k i n g
C H A P T E R 5 . B r a in M e c h a n i s m s a n d B e l i ef 6 0
F o r m a t i o n
C H A P T E R 6 . T h e S e a r c h f o r M o d u l a r i t y 8 1
C H A P T E R 7 . M o d u l a r i ty a n d M e m o r y 1 0 0
C H A P T E R 8 . B ra i n M o d u l e s a n d t h e 1 1 7
U n c o n s c i o u s
C H A P T E R 9 . P s y c h o l o g i c a l A s p e c t s o f 1 3 6
M o d u l a r i t y
C H A P T E R 1 0 . S e t ti n g t h e H u m a n C o n t e x t: 1 4 7
N o t e s f r o m P r e h i s t o r y
C H A P T E R 1 1 . O n t h e I n e v i t a b il i t y o f 1 6 5
R e l i g i o u s B e l i e f s
C H A P T E R 1 2 . A f t er H o u r s 1 8 2
N O T E S 2 0 5
I N D E X 2 1 3
vii
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PREFACE
THIS IS A STORY about a scientific discovery, about i ts
evolut ion and ultimately i ts effect on my personal u nderstand ing
of social process.
Looking back over the last twenty-five years, I see how l i ttle
we can foretel l our future. From personal habits to scientific
pursuits , our year-to-year endeavors change in ways that are
total ly unpredictable. What do not change are initial unanswered
ques t ions and, for me, those centered on how bra in sc i ence
might address problems of personal consciousness and through
those a wider unde rstanding of social processes. Some highly
intel l igent people can marvel over the elucidation of a phenom
enon and are quite happy to leave i t hanging in a factual capsule.
Others are plagued with the secondary question of how a fact
relates to a value, or to a personal understanding of l i fe. While
most scientific facts do not directly relate to broader social
real i ties , some do. I think I have come across such connections,
which is one reason for my writing this book.
In this book I recoun t how m y experienc e in brain and
psychological research has led to a mechanistic understanding
of the way our brains are organized to generate our cognitions
and, ultimately, our bel iefs . Personal bel iefs are what we are al l
about . We l ive and die by our commitments to part i cular v i ews
of l i fe. What is i t about the human brain that finds the formation
of bel iefs so central to i ts operation? Is there an identifiable logic
to human bra in organiza t ion that predicts which phenomena
relate to bel ief formation? I address these and many other
questio ns, but only after what I hop e is an enlighten ing and
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P r e f a c e
even entertain ing account of my brain research act iv i t ies over
the last twenty-five years.
I tel l the story chronologically, as it happened. My first draft,
however, was not written that way. There I fell into the usual
scientific posture of describing and explaining an idea formally,
in an order that impl ied that the theoret ical construction argued
was preformed in the mind, that substantiat ing experiments were
carried out, and the results were presented to the world as an
inexorable product of cold logic . Of course, precious few p ieces
of human knowledge ever emerge in that way, a l though most
descriptions of scientific odysseys lead the reader to believe that
research always progresses logically.
The story is now presented in three parts. First I relate how
my understanding of the basic principles of brain organization,
as l earned from studying unique populat ions of neurological ly
impaired patients, argues for a particular view of brain function
that I call the modu lar view . The data suggest that our m ental
l ives amount to a reconstruction of the independent act iv i t ies of
the many brain systems we a l l possess . A confederation of
mental systems res ides wi th in us . Metaphorical ly , we humans
are more o f a sociological ent ity than a single unified psychological
entity. We have a social brain.
I then cons ider the impl icat ions of these ideas from the
perspective of archaeology as well as from an interpretation of
historical records related to the formation of religious beliefs. (It
wi l l become obvious later why I make these connections . ) And
finally, in the last chapter, I argue that my basic findings in
brain research lead to a particular view of culture. It is not a
chapter for the t imid . Understanding human b iologic and psy
chologic relations is sti l l a most primitive enterprise. As our
understanding of these processes deepens , so too wi l l our under
standing of social process. Yet, what I hope this chapter will
suggest is that the ultimate and proper task of scientists is to
work on these problems in an attempt to ach ieve such a
synthesis.
P r e f a c e
I am accustomed to writing in a scientific style that requires
references for everyth ing. The wrath of one's col leagues when
they think their ideas are not properly cited can scarcely be
imagined . S ince, however, th i s book i s as much a personal
narrative as a scientific study, I have compromised by providing
source notes only for direct quotes and other specific references.
Thanks are due to the many people and inst i tut ions who
helped me carry out this exercise.
I am most indebted to Jeffrey Hol tzm an, to whom th is book
is dedicated . He encouraged m e and humored m e throughout
my work. His criticisms were unrelenting but always constructive.
His tragic death from Wegener's disease in the spring of 1985
has created an emptiness in my life that will not soon be fi l led.
He was the stuff of science, of l ife. He was unique.
I am indebted to Stephen Koss lyn , Nisson Schechter, Ira
Black, and Michael Posner for their close readings of an early
version of the manuscript, and for their many helpful suggestions.
Thanks a l so go to Edgar Zurif, Gary Lynch, Ofer Bar-Yosef,
and Rober t Som mer vi l l e for their cri t ic i sms. I am also indebted
to many of the principals in my intellectual l ife, including Leon
Fest inger, David Premack, and George Mi l ler. Al l gave help and
suggestions. At a practical level, my secretary, Christine Black,
worked t ireless ly as she a lways does , and Kitty Mi l ler made a
valiant effort to turn my prose into English. Most important, I
thank al l of the wonderfu l patients who made th is work poss ib le .
General support came from the S loan Foundation , the Mc-
Knight Foundation , and the U.S . Publ ic Heal th Service. I was
able to write this particular book as the result of a generous
fel lowship from the John Solom on Guggenh eim Mem orial
Foundation. Finally, my profound thanks to the staff at Basic
Books , and especia l ly to Jo Ann Mil ler, my ed i tor. She made i t
all work.
x i
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The Social Brain
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Drawing by Lorenz; 1 980 The New Yorker Magazine, Inc.
CHAPTER 1
The Interpret ive
Brain
BELIEV IN G i s w ha t w e huma ns do be s t w e ma y be l i e v e t ha t
there i s a God, or that the ACLU does or does not do good
workand we are in fact the only spec ies to do so . What i s
there about the human bra in or mind that endows us with this
unique capacity? And, more important , in what ways does this
remarkable ability relate to how we create and order the world
around us? In this book I propose to demonstrate a new and
vita l l ink between the way our bra ins are organized and the way
we construct be l ie f sa l ink that I hope wi l l he lp us ga in a
greater understanding o f human culture in genera l and o f the
important connect ion between bio log ica l processes and cr i t ica l
issues in human behavior .
Bel ie f s stand a t the end po int o f much o f our cognit ive
activity. They are measurable properties of our mental life and
they are , needless to say , powerful in determining much of what
we accept as true about the world. Beliefs are central to the
human experience , yet unt i l recent ly the topic o f how bel ie f s are
formed and why we are so commit ted to them has been a topic
more for philosophers and novelists than for laboratory scientists.
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T H E S O C I A L B R A I N
However , recent advances in our understanding o f how the bra in
and mind are organized are changing this view. In fact, right
now we humans have more insight into why we behave the way
we do than we have ever had before . And i t i s this knowledge ,
gained in large part from the careful study of neurologically
disordered pat ients , that opens the door to a new understanding
of the f ixed characteristics of our species.
We oegin by taking a new view of the organization of the
bra initself. Many preva lent theories about human thought have
argued that problem so lv ing occurs on ly a t the leve l o f consc ious
experience and that i t i s the product o f the human language
system per se . It has been a major assumpt ion o f many invest i
gators in psycholog ica l research that the e lemen ts o f our th ought
processes proceed serially in our "consciousness" for construction
into cognit ions. I think this not ion o f l inear , unif ied consc io us
experience is dead wrong .
In contrast, I argue that the human brain has a modular-type
organizat ion. By modulari ty I mean that the bra in is organized
into relatively independent functioning units that work in parallel.
The mind is not an indiv is ible whole , operat ing in a s ing le way
to so lve a l l problems. Rather , there are many speci f ic and
identifiably different units of the mind dealing with all the
informat ion they are exposed to . The vast and r ich informat ion
imping ing on our bra ins i s broken up into parts , and many
systems start a t once to work on i t . These modular act iv i t ies
frequently operate apart from our conscious verbal selves. That
does not mean they are "unconscious" or "preconsc ious" pro
cesses and outside our capacity to i so la te and understand them.
Rather , they are processes go ing on in para l le l to our consc ious
thought , and contr ibut ing to our consc ious structure in ident i f i
able ways. At the leve l o f consc ious experience , we frequent ly
ask ourse lves where part icular ideas came from when they appear
in our consc iousness . For example , when we write , we suddenly
think o f the exact way to phrase an idea . Where does such an
insight come from? We don't seem to know. We seem only to
4
T h e I n t e r p r e t i v e B r a i n
have access to the product o f these bra in modules and not to
the process itself.
These re la t ive ly independent modular unit s can actua l ly dis
charge and produce real behaviors. With regular frequency we
find ourselves engaged in activit ies that seem to come out of
nowhere . Everything from eat ing a typica l foods to forming
uncommon re la t ionships occurs, and a t one leve l these act iv i t ies
appear to start up from scratch. Through experiments to be
reported in this book, we are beg inning to learn how this
occurrence comes about a t a mechanist ic leve l .
The rea l iza t ion that the mind has a modular organizat ion
suggests that some of our behavior should be accepted as
capric ious and that a part icular behav ior might have no or ig ins
in our consc ious thought process . For example , we just happen
to eat frogs' legs for the f irst t ime or we decide to read a different
kind o f book. But as we sha l l see , we humans resist the
interpretat ion that such behaviors are capric ious because we
seem to be endowed with an endless capacity to generate
hypotheses as to why we engage in any behavior .
In short , our spec ies has a spec ia l bra in component I wi l l ca l l
the "interpreter ." Even though a behav ior produced by one o f
these modules can be expressed a t any t ime during our waking
hours, this spec ia l interpreter accommodates and instant ly con
structs a theory to expla in why the behavior occurred. While the
interpreter does not actua l ly know why there was an impulse to
cons um e frogs' leg it might hypothesize , "B ecause I want to
learn about French food." Th is spec ia l capacity , which is a brain
component found in the le f t dominant hemisphere o f r ight -
handed humans, revea ls how important the carry ing out o f
behaviors i s for the format ion o f many theories about the self.
The dynamics that ex ist between our mind modules and our
left-brain interpreter module are responsible for the generation
of human bel ie f s .
Once one becomes sensi t ive to how strongly behav ior guides
our bel ie f s and how they are formed, one becomes aware o f the
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T H E S O C I A L B R A I N
6
T h e I n t e r p r e t i v e B r a i n
as freely willed. At a psychological level, Albert Einstein felt he
was act ing free ly even though inte l lectua l ly he was c o mmi t t e d
to the idea of a mechanist ic universe . The be l ie f thatwe act of
o ur own free will is such a powerful one it must result from a
basic feature of human bra in organizat ion. I propose that this
bel ie f fo l lows from the modular theory of mind that wi l l be
expl ica ted here . Sincewe are cont inual ly interpret ing behaviors
produced by independent bra in modules as behav iors that are
pr o duc e dby the self, wec o m eto thec o nc l us i o n , w h i c his largely
illusionary, that we are acting freely. I will argue that it is this
inescapable personal perception that f inds
our
be l ie f s becom ing
alteredthe way theydo in response to a variety of social forces.
In this book I explore with the reader the scientif ic evidence
thathas led me to these v iews. Much of the story is a bo ut the
exci t ing discoveries of me nt a l me c ha n i sms as they have beco me
more genera l ly understood by our studies of the brain. But I
ho pe to go beyond this to place those f indings into a larger
socia l context , a context that surely interacts with the physical
natureof our spec ies ,but is one that is usua l ly notadd ressed.
Basic cognit ive phenomena , such as acquir ing and ho lding
social beliefs, are just as m u c h a product of human bra in
organizat ion as our desires to eat, s leep, and ha v e sex. These
specia l human propert ies of the m i n d are the result of brain
organizat ion, and as such revea l that many of the surface
differences
in
cultural beliefs
are the
inev itable product
of how
the brain interprets the ma ny mi l i e us of this world. We kno w
that the four or so bi l l ion people on this earth have the sa me
type of brain and that our spec ies has possessed this type of
brain for at least forty thousand years. It is an awesome fact ,
one that g ives me hope that by d i v i n i ng the brain's nature we
wil l becom e enl ightened aboutthemechanism s o f be l ie f format ion
and conseq uent ly more to lerant o f the diversi ty o f human bel ie fs .
U nde r s t a nd i ng the brain processes that lead to the format ion
a nd ma i n t e na nc e of be l ie f systems g ives us a foundat ion for
7
i mpo r t a nc e
of the
overarching soc ia l structure . Thus,
an
env i
ronment that condit ions someof our me nt a l mo du l e s to act ions
that
may not be in the
long-term best interests
of our
general
bel ie f systems ought to be avo ided. For e x a mpl e , a belief in
marital fidelity might
be
seriously challenged when
at a
Christmas
partyyou f ind yourse l f succumbingto the attractive advances of
s o m e o n e
new.
Tha t
is,
possible rewards from
the
e nv i r o nme nt
could find their mark in one of the mo dul e s , w h i c h in turn
generates
a
behav ior . That behav ior , once carried
out,
m u s t
be
interpreted, and the new be l ie f about the va lue of fidelity that
results
may
wel l
be at
odds with o ther va lues.
As we
c o m e
to
appreciate this process we gain a greater understanding of the
bio log ica l basis
of
cultural p heno men a .
Human bra in research urges the v iew that our bra ins are
organized in suc h a way that many menta l systems coex ist in
w h a tmay be t ho ug htof as a confederat ion. The findings of this
research also suggest that identif iable regionsof the human bra in
a l low for certa in computat ions that make our spec ies the only
one capable of high-order, abstract inference, and that out of
this spec ia l inference-making capacity comesthe unique capacity
to interpret our mult iple self. These interpretat ions can actually
create beliefs. The possession of beliefs is a me c ha n i sm our
species uses to free itself from being in a simple reflexlike
relation with the rewards and pun i shme nt s of soc iety . At the
sa me t i me , w he n
our
interpret ive bra in, which generates
our
personal sets of beliefs, is o v e r w he l me d by the ma g n i t ude and
frequency of such rewards, it can fall victim to new beliefs that
may formas a result of reflexively havingto interpretthe elicited
behaviors .
Rela ted to these principles of bra in operat ion is the personal
percept ion humans possess that they act of their own free will.
Civ i l ized, educated, twent ieth-century humans, some even con
trary to the ir working knowledge of modern physics , be l ieve
theyare freely acting agents. Even habitual behaviorsare v iewed
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T H E S O C I A L B R A I N
understanding more c lear ly the basics o f human menta l l i f e . But
in order to accompany me on the journey through my experiences
in brain research that lead up to these ideas, it is important for
readers to grasp certain basic principles of brain organization,
which I turn to now in chapter 2 . Once these pr inciples are
understood, the larger issues of how the brain actually produces
cognit ion and bel ie fs bec om e a joy to discover .
8
CHAPTER 2
Basic Brain
Principles
U N D ER STA N D IN G t he br a i n ' s r e l a t i o n t o ba s i c i s sue s o f
human nature ra ises some deep quest ions about knowledge o f
the structure and function of that particular piece of biological
tissue. The majority of scientists see the brain itself as endlessly
modif iable and ever-responsive to env ironmenta l cont ingencies .
To them, the mind o f a human just born into the world is ra ther
empty, but ready to be f illed up and structured by the cultural
env ironment . Those who ho ld such a v iew look with suspic ion
on findings that seem to suggest there are set properties to brain
tissue that impose specific features on the mind. In order to
learn more about how principles o f bra in organizat ion re la te to
cognit ion, we must f irst learn something about certa in main
features o f bra in development and about the ir psycholog ica l
correlates. In short, one needs to know what brain tissue is like.
How does i t work? How does i t respond to experience? What
l imits does the nature o f this t i ssue put on any theoriz ing about
our species?
How such quest ions might be answered began to be revea led
to me about twenty-five years ago when I read a most intriguing
article in Scientific American writ ten by my future mentor ,
Roger W. Sperry .
1
I was then an undergraduate a t Dartmo uth
College. He was one of the foremost brain scientists in the world,
9
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T H E S O C I A L B R A I N
the Hixon Professor o f Psychobio logy a t the Cal i fornia Inst i tute
of Technology (Caltech). Sperry's article explored how nerve
circuit s grow to spec i f ic places in the bra in. For example , how
does a frog's optic nerve, the nerve that will carry information
about what the frog sees, f ind its way from the eye to its proper
connect ion in the bra in? Any explanat ion o f such matters must
draw on the knowledge o f how the bra in is structured by the
genet ic code , and what are i t s l imits for change in response to
env ironmenta l events . Understanding how nerves grow is about
as fundamenta l as things get in learning about the bra in.
The 1960s were go lden years for American sc ience , when
almost every reasonable research program could get funded. On
what I thought was a long shot, I wrote to ask Sperry for a
summer job between my junior and senior years. My home was
close to Caltech, and I thought i t would be perfect . To my
surprise, he wrote back saying that it would not only be possible
but that the Nat iona l Sc ience Foun dat ion had sum mer fe l lowships
for the likes of
m e .
I couldn't be l ieve i t, but nonetheless m anaged
to accept the o f fer . That summer proved to be the pivota l ten
weeks of my life.
The lab was exceeding ly cordia l , and Sperry , who was a lready
something o f a legend, welcomed me with every courtesy . I was
the lowest underling in the lab; but as in any large lab there
were other underlings there who were generally available as
companions and who taught me not only about the bra in but
about sc ience in genera l . I t was my good luck to get to know a
most art icula te and enthusiast ic young psycholog ist , Mitchel l
Gl ickste in, who now, a f ter years in American universi t ies , i s a
professor a t Universi ty Col lege in London. Gl ickste in was do ing
f ine work a t Caltech but a lso was one o f those memorab le people
who gave free ly o f his t ime to teach neophytes l ike me. He was,
and still is, a wonderful scholar and teacher, and I learned much
from him.
My f irst order o f business was to become famil iar with the
early experiments done by Sperry . I was soon to learn that any
10
B a s i c B r a i n P r i n c i p l e s
bio log ica l ly educated person is amazed by those who mainta in
the tabula rasa theory, that all brains start this life more or less
the same. That idea , welded onto the American psyche by the
Constitution, was forcefully argued in the intellectual community
by the psycholog ist , John B. Watson. Watson was the recognized
spokesm an for an American react ion aga inst German Rat iona l ism
and the fragility of introspective evidence when taken as scientif ic
e v i d e n c e .
2
His v iews came to rest on two major considerat ions.
The f irst i s that the manipulat ion o f reward cont ingencies can
be a powerful determinant o f behav ior , especia l ly in animals .
The second is that interact ion with the env ironment g ives the
nervous system i t s structure . Watson made his case a t a t ime
when the bra in sc iences were young and sc ient ist s were largely
ignorant of how the brain is built . In fact, it could be argued
that when Watson was proposing his theories he was actua l ly
encouraged by contemporary bio log ica l research that the bra in
was infinitely plastic. At that t ime, in the early 1930s, the
accepted v iew in bra in sc ience was that "funct ion precedes
form," that an arm had to be used as an arm before the neurons
innervat ing the arm became speci f ied for that purpose . In short ,
the bio log ic v iew was the equiva lent o f the psycholog ic v iew of
the newborn organism being born with a c lean s la te .
. Sperry's work he lped to set things straight. He sho wed that
the intr icate neura l networks that manage and contro l the
appendages are established during deve lopm ent and are careful ly
formed and bui l t under the contro l o f genet ic mechanisms^
These c ircuit s become set in the ir ways ear ly in l i f e and theif~
capacities are strictly limited and defined at that t ime. The
implicat ion o f this work on the per iphera l nervous system is
that many central circuits of the brain are the same, such that
each person's individual nature reflects his or her underlying,
genet ica l ly prescr ibed neura l organizat ion. How bra ins adopt
psycholog ica l character depends not only on acc idents o f env i
ronmenta l events but a lso on the ir innate architecture .
This work began a t the Universi ty o f Chicago when Sperry ,
n
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T H E S O C I A L B R A I N
12
B a s i c B r a i n P r i n c i p l e s
Figure 2 . 1 . A n example o f Sperry's work o n neurospecificity. T he
neurons from th e fish ey e that ha d been cu t grow back to their proper,
exact places in thebrain, bypassing incorrect zones (start at top left and
follow arrows).
issue, working with data, talking about the biologic context, gave
all of us in Sperry's lab a deep respect for the genetic component
in our lives.
It is also important to realize that a developing biologic system
such as the nervous system is under tight, but not altogether
comp lete , genet ic contro l ) A vast numb er o f env ironm enta l
influences arise around the organismexternal forces of the
3
still a graduate student, questioned the views of his famous
mentor , Paul Weiss .
3
The thrust of Sperry's research was that
nerves grow in prespecified ways to their destination points.
T h u s ,
contrary to Weiss's view, nerves grow out to a limb
already centrally specified through genetically controlled mech
anisms. Nerves do not grow out in a random way and then have
the peripheral structure they happen onto specify what they do.
1
Nerves are predestined to do particular jobs and they find the
right peripheral t issues to connect with. For example, if in a rat
the left hind leg nerve is experimentally diverted through surgical
manipulation into the right hind leg, the right hind leg begins
to act as if it were the left hind leg. And the situation remains
this way for the life of the rat.
4
In other classic experiments Sperry cut the optic nerve of a
goldfish and studied how specifically it would grow back to the
proper po ints o f connect ion in the bra in itself. Here, instead of
looking at the specificity of nerves growing out of the central
nervous system, he was assessing the kind of specificity for
nerves growing into the central nervous system, the seat of
important psycholog ica l processes . The regenerat ive process was
most exact, with specific retinal points represented by particular
neurons finding their way to definite regions in the f ish's visual
system. If the neurons were diverted into an incorrect area, they
would grow through foreign zones and find the right part of the
brain (see f igure 2.1).
Sperry's model, which has now been verified through thousands
of examples , i s that "form precedes funct ion."
5
Currently there
are several theories about what the exact, biologic mechanism is
by which a nerve knows where to grow. The ident i f ica t ion o f
that mechanism is not set t led.
6
No one , however , now doubts
that the neuronal system develops under tight genetic control.
Personal brain organization also is under tight genetic control
and is not easily perturbable by environmental influence. Sperry
showed that spec i f ic neuronal connect ions were made under
direct ion o f the genome, not the env ironment . And studying the
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T H E S O C I A L B R A I N
mother as well as forces from the outside physical environment.
The force of gravity causes water to f low downhill, but the water
can be diverted from a seemingly predestined course by the
judic ious placement o f a rock. In the bio log ic context o f the
brain, it is probably more accurate to say that with our present
knowledge , m ost o f these inf luences remain unspeci f ied, but
they are definitely there. Comparison of the brairts of siblings,
or perhaps even those o f ident ica l twins a t a postmortem , revea ls
gross dif ferences in m orphology; the varia t ions in the microstruc-
ture of the cell-to-cell organization are staggering. Since the
brains of close cohorts are different, it is not diff icult to imagine
the wide range o f var ia t ion in the rest o f the populat ion. Whereas
everybody has a left and a right hemisphere, a midbrain, and a
visual cortex, the prop ortion of cells in each of these jjystems
and how they interconnect varies from person to person)
An intr iguing thought i s to consider whether the bra in varia
t ions among indiv iduals underl ie the psycholog ica l var ia t ions
among normal adult s . Although everybody responds to rewards,
for example , some people respond with greater intensi ty . Could
this difference in intensity be reflected in a differential projection
of neurons to a part o f the bra in that mediates the chemica l
mechanism responsible for the ef fect? In o ther words, do people
who are exquisitely sensitive to f lattery or the appreciation of
external goods have brains with a larger than usual projection
to the reward system of the brain?
With genet ics supply ing the m ain framework for neura l growth
and development , i t i s now recognized that there are def ini te
t ime periods during development when bra in organizat ion is
modifiable. These periods for change are short and are presently
known for only a few species and a few kinds o f experience .
Some of the best examples come from studies on the cat 's v isua l
system. In Nobel-Prize-winning research, Harvard neurophysi -
o log ist s David Hubel and Torsten Wiese l descr ibed the normal
cellular architecture of the visual cortex.
7
They discovered that
in both the adult and newborn cat an ident ica l organizat ion
B a s i c B r a i n P r i n c i p l e s
exists,
consist ing o f predetermined proport ions o f ce l l s that
respond to particular orientation of light and dark edges presented
in the cat's real f ield of vision. Some cells respond to leftward
leaning l ines , some to r ightward, some to vert ica l , some to
horizonta l , and some to o ther or ientat ions found in between
these extremes. Other features inc lude the number o f ce l l s that
rece ive informat ion from just one eye as opposed to both eyes .
Since the pioneering studies carr ied out in the 1 960s, a num ber
of subsequent invest igators have shown that there i s a t ime
period during the first weeks of a kitten's life when exposure to
an abnormal v isua l env ironment can change the proport ion o f
ce l ls commit ted to detect ing l ines o f a part icular or ientat ion.
Thus, if a new kitten sees only lines of a vertical orientation
during the first three weeks of life, more cells will respond to
l ines o f that or ientat ion when the ki t ten is tested a t ten weeks
of age . Lines or edges presented j n nonvert ica l or ientat ions w i l l
tend not to e l ic i t any responses/ Present ing such env ironmenta l
manipulations a few weeks later in a cat's life, say, at ten weeks
S^of age , seems to have no ef fect on the normal organizat ion o f
the visual system. The critical period is over. The brain system
seems set for the duration of the cat's life (see f igure 2.2). \
Another example o f these phenomena , one o f my favorites ,
comes from the work o f Rockefe l ler Universi ty Professor Fer
n a n d o N o t t e b o h m .
8
A young male bird learns his song from the
adult male . If the young male i s exposed to song anyt ime before
he is a year old, he learns the proper song. If he does not hear
the song until after he is a year old, he is never able to learn it .
2?
Th e critical period for learning bird song, then , lasts for on e
year . This per iod o f learning is not unl ike those for humans
during the develop men t o f the ir language and speech. If a young
child does not acquire language by a particular t ime, it never
de v e l o ps no r ma l l y ^
Another way to look a t the re la t ion between bra in growth and
psycholog ica l development i s to examine para l le ls between the
order o f acquisi t ion o f chi ldhood ski l l s and the breakdown of
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N o r m a l c a t V e r t i c a l l y d e p r i v e d c a t H o r i z o n t a l l y d e p r i v e d c a t
Ver t ica l Ver t ica l Ver t ica l
(a) (0
Figure
2. 2
Orientation
o f
lines that elicit
a
response from cells
in the
visual cortex of a cat under three conditions. In (a) the normal
distribution o f responses is shown. In (b ) the responses ar e shown for a
ca t
raised
in an
environment with only horizontal
l ines, and in (c ) the
responsesof a catraised having seen only vertical l ines.Brain organization
c a n be influenced early in l i fe . If the exposure occurs at ten w eeks,
however, these brain changes are not possible.
i
such ski l l s a f ter acquired bra in les ions occur in adulthood.
Parallel deficits may suggest that areas of the brain where damage
in the adult results in loss of a particular function are the same
areas that need to mature in the you ng bra in in order to support
that funct ion. An example wi l l make this c lear .
It has been shown that in young rats a specific brain area
ca l led the dentate gyrus o f the hippocampus is immature for the
first month after birth.
9
W hen these animals are careful ly stud ied,
the young rats are seen to behave l ike adult ra ts with les ions in
this area . In humans this bra in area , the dentate gyrus, matures
after birth as well. As in the rat, the corresponding behavioral
abi l i t ies o f the preschoo l chi ld are not yet whol ly funct ioning
until the crit ical brain areas mature. Thus, there are parallels
between the behavioral abilit ies possible when a structure is
lacking e i ther maturat iona l ly or because o f a les ion. This suggests
that particular brain regions must reach a certain level of
maturity before the behav ior they med iate can be achieved. Ages
five to seven appear to be the key period.
B a s i c B r a i n P r i n c i p l e s
The discovery o f such mechanisms is interest ing from a
num ber o f vantages. F irst , the data show how real env ironme nta l
input can modify the genet ic intent o f an organism. The o ther
side o f the co in, however , suggests that the condit ions under
which such changes can be ef fected are l imited and short - l ived.
Both po ints are o f ex treme importance .
There are o ther important fea tures o f the developing bra in to
consider. The rate of growth varies from one brain to another.
For example , Bi l ly may h ave more o f his cort ical ce l l s jny din ate d
than Bobb y has by the age o f one yea r | Mye l in i s the substance
that wraps around neurons and g ives them each a sheathT^This
sheath changes the microstructure o f the neuron and enables the
neuro n to transmit its electrical imp ulses m ore efficiently. With out
this sheath the neuron is s lugg ish, which is an important consid
erat ion when dea l ing with an intr iguing aspect o f bra in devel
opment , the myel inizat ion o f the cerebra l cortex . Much of
hum an co gnit ive act iv i ty takes place in the cortex . For the cortex
to work ef f ic ient ly , the myel in must be in place . Yet , myel ini
z a t i o n de v e l o ps s l o w l y .
1 0
Some reg ions o f the bra in do not
rece ive the ir ful l complement unt i l the third decade. Again, this
fact raises interesting questions about the brain correlates of
developing psycholog ica l processes .
It i s widely assumed by developmenta l psycholog ist s that
various cognitive stages must be realized in a specified order for
normal cognit ion to occur . Abi l i ty A must be usable before
abi l i ty B can mature , B must be usable before C can mature ,
and so on. Psycholog ist s o f every persuasion argue over the
nature and quality of each of these mental abilit ies, but they all
tend to be l ieve that each step must be completed in i t s proper
order . As a consequence , psycholog ica l models o f development
are created and are discussed as if this psychological process
were the basic bui lding unit for personal cognit ion.
A bio log ica l v iew that a lso honors the unique character o f
psycholog ica l experience could argue this i ssue o f the bui lding
process by c la iming nothing happens a t the psycholog ica l leve l
17
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T H E S O C I A L B R A I N
until the brain areas subserving the requisite psychological
processes are connected and funct ioning . Just as a computer
that has a f ini te capacity cannot process more informat ion than
it has memory chips to handle , the developing organism can do
only so much o f a psycholog ica l job with the neuronal hardware
it has funct ioning . When the organism achieves another leve l o f
capacity , however , the argument would be that the bra in has
maturedmore cort ica l areas have become act ive or more
efficient, making the new psychological ability possible. One
bio log ic possibi l i ty for this further development in the human is
the di f ferent ia l myel inizat ion pat tern in the human cerebrum.
The myel inizat ion process i s a de layed one and matures only in
the brain areas most responsible for cognition at about the t ime
a particular skill is realized in a young child.
Another important pr inciple about the developing bra in is
that , when a l l i s sa id and done, a l l s tudies to date have shown
that environmental influences affect the brain only in a negative
way . This fact stands in marked contrast to the c la ims about the
importan ce o f ear ly env iron ment , mu ch o f which com e from
brain researchers themselves . The only t ime in the natura l
history of an organism that it is operating at its full, undisturbed
genetic potential is following an uneventful birth. This full neural
deck, as i t were , becomes di luted only by physica l events
imping ing on the bra in. Head injury , endocrine imbalances,
nutritional adversities, all act negatively. Contrary to what many
. claim, there are no conv incin g data that an enriched enviro nm ent
can change brain power positively. This point is worth considering
in some detail.
Many sc ient ist s were pleased when a group of biopsycholog ist s
started reporting in the 1960s that rats raised in an enriched
environment as compared to contro l ra ts had thicker , more
complex cort ica l neura l c ircuitry ." The c la im was that the ir
bra ins were bet ter and more capable o f carry ing out problem
solv ing . Those who bel ieve strongly in the inf luences o f env iron
ment , a v iew shared by those people that more or less "own"
18
B a s i c B r a i n P r i n c i p l e s
the pr imary and secondary schoo l establ ishments , were thr i l led
and used this new "biologic data" to argue for greater control
over ear ly env ironment . Implic i t in the ir rhetor ic was the idea
that superkids could be created. Suddenly the env ironmenta l ly
minded abandoned their usua l distrust o f bio log ic sta tements
that suggest each of us has a predestined limited capacity, and
they instead argued on the strength o f this supposed bio log ic
data that the brain capacity could be enhanced.
Since these studies began, the experimenters themselves have
not lost their faith in these claims, which is a normal circumstance.
The n eurobio log ic co mm un ity a t large , however , i s less sanguine .
First , the studies had and continue to have a basic design flaw.
The so -ca l led enriched animals are compared to so -ca l led normal
litter mates. But what is called enriched is most likely normal
and what i s ca l led normal i s most l ike ly deprived. What the
experimenters do is place one group in an env ironment ful l o f
toys and co lors and they frequent ly handle them. In short , the
animals rece ive st imulat ion. They experience something l ike a
normal env ironment . The contro l or nonst imulated rats , on the
other hand, stay in a small rat cage in a strict environmentally
contro l led animal room and basica l ly lead a deprived l i fe .
Baselines are relative, and in this case the baseline was mislabeled.
The second major development in developmenta l neurobio logy
that undercuts the v iew that experience enhance s cort ica l growth
is the discovery that the developing bra in over innervates a l l
a r e a s . '
2
Th is mea ns that if brain area A send s projections to
bra in area B, those project ions in the young bra in can be seven
times denser than projections existing in the adult brain. It is
not yet known how and why neurons succeed in establ ishing
proper connections in the appropriate brain areas, but it is
known that bra in development starts out rapidly and then s lows
do w n.
But because the developing brain is so delicate, it can be
slowed down early on by an interruption or injury. This has
been clearly shown at the clinical level. Brain injury to either
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20
B a s i c B r a i n P r i n c i p l e s
adolescence, the brain becomes neurologically set . Its long con
necting circuits transmit information in specified ways, and
injury to these c ircuit s causes permanent impairment . This i s
not to say that no recovery is possible. What is at issue with
cases o f injury , however , i s the mechanism of improvement . It
appears likely that undamaged brain areas begin to regulate the
behavior that has been disrupted or lost , usually by applying a
new b ehavioral strategy (T hu s, what appears to be brain repair
is not recovery of damaged brain tissue, but adaptation by tissue
that has not been damaged. That i s the "hard" v iew. Some are
more hopeful in neuro science . I am not.
And how is the mature , normally developed bra in organized?
What is the structural logic that allows it to do the kind of tasks
we humans do so wel l?
When I started doing brain research in the early 1960s, the
brain was considered a much simpler organ than ensuing research
has shown it to be. It was assumed then that sensory pathways
conveyed sensory informat ion to the cortex and there , in asso
c ia t ion areas, the informat ion combined with o ther processes to
organize neural messages to be sent to the motor or response
part o f the bra in.
1 4
With few except ions there was a pervasive
"st imulus and response" menta l i ty to both bra in sc ience and
much of psychology . The psycholog ica l v iew was strangl ing the
field of cognition. The biological view was static, waiting for
new techniques. These techniques were developed, and now af ter
thousands of studies, they have revealed in a profound sense
how the adult bra in is organized.
15
And the advances in def ining
the adult brain over the past several years have been most
remarkable.
It has been said that the "gain in brain is mainly in the stain."
In the ear ly 1970s new chemica l sta ins were developed that
allowed more sensitive tracking of neuronal pathways; new
structura l re la t ions were discovered. This discovery , combined
with an ever-evo lv ing set o f neurophysio log ica l techniques,
unearthed the new logic about brain organization.
21
hemisphere during the chi ldhood years causes a marked decrease
in verba l IQ.
1 3
This conclusion is based on comparison o f the
verbal IQ range of an injured child with the verbal IQ range of
his or her siblings. Relative to them, the injured child is severely
impaired, a statistic that is at odds with the usual family profile
of IQ for siblings.
An important aspect o f this developmenta l data on IQ is that
the detrimental effect of experiencing an early head injury is
more acutely apparent if the injury occurs before the age of one.
[jnjuries occurring after this age have less effect on verbal IQ?\
Th is obser vation , whi ch is a robust clinical f inding, unv eils
another complex and intr iguing feature o f bra in development .
The very immature brain is in such a delicate dynamic state
that any insult to its growth pattern disrupts its ultimate upward
potential. While the injury is occurring at a t ime when the brain
is presumed to be most capable of self-repair, it is simultaneously
a time when the brain is most vulnerable to any interruption of
normal growth. At the same time, the effects of an injury
occurring anytime after the f irst year have less to do with general
' intelligence and more to do with specific skills. Thi s me ans that
at a very early age, the specialized functions of each half-brain
are expressing themselves and with brain injury are irreparably
damaged or lost .
What emerges is a picture of a brain that is a mosaic of neural
centers behav ing in de l ica te and dynamic interre la t ion during
the early years. The parts of the brain that are not responsible
for the management of adult cognitive skills are very active in
establishing these cognitive processes in particular brain areas
during development. The brain is aswirl with activity. Yet just
as quickly as it starts, this activity stops when the specialized
capacities of the adult have reached their f inal stage. When the
brain system has reached maturity, changes in its abilit ies appear
restricted to its capacity to learn, and this capacity differs from
person to person.
After the early years of development, by the t ime of a person's
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Until this t ime the brain was viewed as a single integrated
system that gave rise to a unified cognitive process. Sensory
information was projected to one part of the brain for any
particular modality such as vision. Upon arriving in the brain,
the information was elaborated in visual association areas; and
from these areas a message was somehow sent to the equally
discretely defined motor system, allowing for an appropriate
response. This sensory information was analyzed to a greater
degree at each stage along the way. Thus, at the f irst stage of the
visual process, brain cells responded only to simple primitive
visual stimuli such as edges or corners. As cells were stimulated
in deeper levels of the brain's visual system, where more complex
computations were possible, responses to more specific features
of the visual world were generated. The notion was actually
proposed that cells in some part of the advanced visual areas
responded to such specific things as pictures of hands, or brushes,
or f ixes; as a result they became known as "grandmother cells,"
or cells that would specifically respond to particular stimuli,
such as one's grandmother .
With the aid of new stains and other techniques, it was
discovered that the primary visual information coming in from
a sensory surface such as the retina projected to a variety of
places in the brain. To be sure, their primary projections were
to the already well-recognized primary areas. But the new cell
stains revealed important secondary projections (see f igure 2.3).
This ra ised the quest ion o f what anim als would see i f the pr imary
projections were destroyed, leaving intact only the secondary
projection areas. Experiments were performed on all kinds of
animals. On humans, the effects of naturally occurring lesions
to the primary visual system were observed. The results were
uniformly str iking . Animals could see complex st imul i without
their primary visual systems. The earlier notion of a linear path
of sensory informat ion into more and more complex construc
tions f inally terminating in the perception of a discrete object
underwent rev is ion. There was a redundancy quot ient to bra in
22
B a s i c B r a i n P r i n c i p l e s
C a t - 1 9 6 5
RETINA
L6N
u
ECTUM
CORTEX
AREA
17
C a t - 1 9 8 5
RETINA
b)
LGN
TECTUM
A
A
1
B
MININ
ARE A
17
18
19
1 AT
Figure 2 .3 In (a) the hierarchical view o f theorganization of the visual
system is depicted. In recent years this view ha s given way to the one
indicated in (b) , where th e visual system is multiply represented a nd
incoming fibers ar e projected to many brain zones simultaneously.
organizat ion. Sensory informat ion is now v iewed as be ing mul
t iply represented in separate and somewhat independent pro
c e s s i ng mo dul e s .
1 6
The actua l mechanism by which one sees
one's grandmother, in both real life and in the mind's eye,
remains elusive. For present purposes, it is important to appreciate
that the adult brain is not organized as a unitary monolithic
system, with each part linked to every other in some kind of
hierarchical way. In short, instead of information being processed
serially, it now is clear there is much parallel processing.
While anatomists have been discovering the complex ity o f the
basic neural architecture, neurochemists have been unearthing
multitudes of specific chemicals that allow one neuron to "talk"
2
3
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24
B a s i c B r a i n P r i n c i p l e s
their intensi ty . These modulat ing inf luences
are
possible m ost
clearly in human beings, where the ex istence of be l ie f systems
can override primitive brain responses
to
env ironmenta l ly induced
painful and pleasurable events.
Another important bra in principle is that the a m o u n t of pa in
and pleasure an organism can experience is finite. The chemica l
systems that mediate these funct ions are f inite. They reach a
peak, and a t temptstoe l ic i t responsesto m o r eof the st imulat ion
in quest ion are wasted effort. Finally, especially in t h i s do ma i n ,
individual differences aree n o r m o u s . One person's level for pa in
m a y be another's level for only mild discomfort . The sa me is
truefor pleasure. Recent studiesareshow ing that these individual
varia t ions are most l ike ly due to different structural capacities
in a person's bra in. Jones's capacity to ma ke e ndo r ph i ns may
be different from Smith'sor hiscapacity to respond to the self-
ma de c he mi c a l smay be different. Thep ossibi l i t iesfor expla ining
so ma ny d i me ns i o ns ofp ersonal i ty are breathtaking.
My short tutorial is over . I h o p e I have imparted some
understanding of the natureof the bra in. These few g l impses of
basic bra in mechanisms aresufficient to tellus w ha twe ne e d to
kno w a bo ut the basic nature of the t issue. Four principles
emerge: (a) the bra in develops under t ight genet ic contro l; (b)
its basic architecturecan be modified only very early in lifeand
then only in a negat ive way; (c) it is organized in such a way
that re la t ive ly independent processing modules ex ist everywhere
throughout the bra in system; and (d) it has m e t h o d s of self-
modulat ing inf luences fromthe env ironment throughan intricate,
se l f -governed bra in chemica l system.
T h a t s u m m e r of 1960 c o nv i nc e d me that brain science,
especia l ly
in
t e r ms
of
behav ior , would
be my
life's work.
I
a ssume d t ha t I would finish my premed studies and trot off to
me di c a l s c ho o l as everyone expected me to. Back in Hanover ,
however , l i f e
was not the
sa me .
I
couldn't
get the
s u m m e r
experienceout of my mind. F ina l ly I wrote Sperry and asked if
25
t o a no t he r .
1 7
These chemica ls , which are secretedby the axonal
ti p of neurons, change the chemica l mil ieu in and a r o und
adjacent neurons. This chemica l change is what a l lows the
neuronal message to pass from one ne ur o n to another . , Modern
brain research shows that particular neurons are responsive to
certa in kinds of chemica ls (ca l led neurotransmit ters) and not to
others. As a c o nse que nc e of these com ple x findings, it is now
recognized that in addit ion to mult iple sensory representat ions,
thereare mult iple chemica l systems.And, in all l ike l ihood, each
chemica l system is specifically involved in particular functions
when act ive in particular brain regions. Parkinson's disease is a
casein po int .It is a c c o mpa ni e d by a spec i fic chemica l def ic iency
in a specific brain region. \
Other recent correlative neurochemical discoveries have proved
equal ly fasc inat ing . These have to do w i t h the body's chemic a l
systems that he lp modulate pa in
and
pleasure ,
and
perhaps also
such basic activit iesas s l e e p .
1 8
One such discoveryis of the wel l -
publ ic ized, se l f -produced opia tes ca l led endorphins which
are
crucial to a body's wel l -be ing . These chemica ls are activated
under condit ions
of
bodily stress
and
serve
to
c ur b so me
of the
painwe would o therwise fee l in the ir absence . Thereis no do ubt
that
we
would fee l more pa in without them.
A
drug called
N a l o x o ne b l o c ks the act ion of these se l f -produced opia tes and,
if
it is
administered after heavy exercise
or a
pa inful st imulus,
the discomfort
is
greatly increased.
These advances in brain research and related fields are of
major importance to the understanding of how the brain func
t i o n s ,
and any interested reader should investigate them further
to learn moreof the considerable deta i ls .For my purposes here ,
I just want
my
readers
to be
aware
of
their existence. They tell
us that physica land ident i f iable bra in mechanismsare governing
s o m e
of our
most personal experiences. Th ey te l l
us
that
at
some basic leve l env ironmenta l cont ingencies do work because
they elicit specific brain action.
But
they also tell
us
that
the
brain itself regulates these actionsand can mo dul a t e or e nha nc e
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he would sponsor an appl icat ion for me to do graduate studies
with him. He sa id he would be de l ighted, and so largely through
his support I was admit ted to Caltech the fo l lowing summer.
This change wasn't the easiest thing to expla in to my fa ther ,
a physic ian passionate ly invo lved with medic ine . My brother
was in medica l schoo l a t the t ime and I was expected to fo l low
suit . My father, who had been born into a large Italian family,
thought medic ine was one o f the most honorable professions a
man could pursue . He kept te l l ing me that I couldn't rea l ize this
until I actually practiced it . He had gone to medical school
because , upon his graduat ion from St . Anselm's in New Hamp
shire , the monsignor had ca l led him in and to ld him he should
go to Loyola in Chicago. Although it was late June, the monsignor
had sa id he would make a l l o f the arrangements . My fa ther
protested, say ing he had never even taken chemistry in co l lege .
The monsignor sa id, "So what? Learn i t over the summer, and
while you are at it learn a litt le physics. The boys in Chicago
think you have ." He added, winking , "and you had bet ter not
make a l iar out o f me. I a lso to ld them you were seventh in
your c lass . I didn't te l l him there were only seven in the c lass ."
This method o f ga ining admission to medica l schoo l i s no longer
available, but I am not at all sure that the current methods are
any wiser. My father, by all accounts, was an extraordinary
surgeon. Wh en I to ld him about m y change in plans he m erely
smiled and muttered something to the ef fect that he thought this
might be the case . Then he sa id, "Whatever you want i s okay
by me . I just don't understand wh y you w ould wan t to be a
P h . D . when you can a lways hire one ." He had me there .
26
CHAPTER 3
Split-Brain Studies:
T he Early Years
TH ER E IS an ax iom in bio log ica l c irc les sta t ing that i f you w ant
to understand how something works, you study i t funct ioning
in disrepair. If a trained scientist were confronted with a television
set for the f irst t ime and asked to f igure out how it works, the
task would be easier if the set did not function properly. With
the picture fluttering, hypotheses could be immediately formed
about i t s underly ing composit ion, and the sc ient ist would be on
the way to understanding how i t works.
The same approach can be used to understand how the human
brain generates and susta ins normal human cognit ion. The
neurologic patient suffering from a disease that disrupts normal
brain relations can generate rich insights into basic brain orga
nizat ion. More important , the study o f the disrupted bra in
teaches us how the cognit ive system i t se l f i s normally organized.
As a consequence , neuro log ic pat ients produce informat ion a t
two levels. They tell us about brain principles and about cognitive
principles. This f ield of endeavor is formally called cognitive
neurosc ience , and research in this area has occupied most o f my
time for the past twenty-five years. Much of this work is pivotal
to my present arguments .
In brief, research on the neurologic patient will allow claims
to be made about certain crucial features of brain organization
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and personal cognit ion. As I 've a lready ment ioned, i t wi l l
become c lear that , contrary to our intense introspect ions, con
sciousness is not an indivisible unitary process. Instead, what
appears to be personal consc ious unity i s the product o f a vast
array of separate and relatively independent mental systems that
cont inual ly process informat ion from both the human interna l
and externa l env ironment . Put in more genera l terms, the
hum an m ind is mo re o f a soc io log ica l ent i ty than a psycholog ica l
ent i ty . That i s , the human mind is composed o f a vast number
of more e lementary unit s , and many o f these unit s are capable
of carrying out rather sophisticated mental work. These activit ies
can go on outside the awareness o f our verba l consc ious system.
Putting it the other way around, extensive information processing
in the brain is going on independent of verbal processes. Further,
the management o f these separate systems is the chore o f the
normally dominant computat iona l systems o f the le f t ha lf -bra in.
What also emerges from recent research is that these left-brain
computat iona l systems are c lose ly t ied to language processes but
are not the language system per se. It is the appreciation of these
aspects of brain organization that suggest new insights into how
menta l phenomena such as personal be l ie f s are formed and
maintained, and how, as a result of their reflexive presence in
the human mind, the s imple e f fects o f ex terna l cont ingencies
can be overruled. The bulk of the work suggesting these views
comes from split-brain research, and I will begin, logically, at
the beg inning .
That summer a t Caltech in 1960 , I learned about Sperry 's
o ther discovery , the spl i t -bra in animal . The term was co ined to
descr ibe a surg ica l procedure performed on cats and monkeys
that disconnected the left brain, or hemisphere, from the right
brain, or hemisphere. In the initial experiments carried out in
the ear ly 1950s by Ronald Myers (who was then a student o f
Sperry's) and Sperry, the aim was to isolate the neural pathways
by which v isua l informat ion presented to one hemisphere was
28
S p l i t - B r a i n S t u d i e s : T h e E a r l y Y e a r s
integrated with that presented to the other.
1
In order to understand
what I am saying, the reader has to consider on ly the page he
or she is reading. Fixate on any letter or word (f igure 3.1). The
human brain, as well as the brains of the cat and monkey, is
organized in such a way that visual information to the left of
the fixated point is projected to the right brain while all visual
information falling to the right of the f ixated point is projected
to the left brain. Yet, you see the visual world as one integrated
whole . Myers and Sperry wanted to f ind out which pathways
were responsible for that integration. They found that out and
much more .
The band that connects the two ha lf -bra ins in mammals i s
ca l led the corpus ca l losum. It i s an enormous tract o f nerve
f ibers (over two hundred mil l ion indiv idual neurons in humans)
and it is easily approachable for surgical sectioning. Severing
this connection as well as a smaller, more anterior structure
ca l led the anter ior commissure iso la tes one hemisphere from the
other. Well, that is almost true. If , in addition, a structure called
the opt ic chiasm is sect ioned in the midl ine , v isua l informat ion
presented to one eye is projected to only one half-brain. Sec
tioning the chiasm is carried out only in animal research (see
figure
3 .2) .
Myers and Sperry discovered that when the corpus ca l losum,
anter ior commissure , and opt ic chiasm were sect ioned, v isua l
discr iminat ions taught to one bra in were not known by the
other. For example, if a cat learned while the right eye was open
but the left was closed that every time it pushed a panel with a
tr iang le on i t , i t would rece ive some l iver pate , i t did not know
that fact subsequently when the left eye was open and the right
was c losed. The informat ion learned by the r ight bra in did not
transfer over to the left brain. In study after study, animals with
sect ioned neura l interconnect ions between the hemispheres be
haved as if they had two separate brains, hence the term "split-
br a i n . "
2
Think for a moment what the impl icat ions are for humans.
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S p l i t - B r a i n S t u d i e s : T h e E a r l y Y e a r s
Figure 3.2 This i s a sagi ttal view of a human b rain. The large fiber
tract (CC) i s the corpu s cal losum. It i s this structure that the neurosurgeon
sect ions in seeking control for otherwise intractable epi lepsy.
Fixate a point on the wal l and hold your f ixat ion . Now imagine
I place to the left of fixation two objects, one an apple and one
an orange. Keep f ixat ing and imagine I t ip toe over and p lace a
one hundred dol lar b i l l under the apple, a l l of th i s going on to
the left of fixation. N ow close y our eyes and just think for a
mo me nt ab out wh ich p iece of fru i t I bai ted . I f you p ick up the
correct fru i t when you open your eyes , you may keep the one
hundred dollars. If you now open your eyes and the fruit is sti l l
to the left of f ixat ion , you would know the answer because the
same hemisphere that saw me p lace the one hundred dol lars
3
1
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under the apple is now being asked about it . If , however, I
moved the apple and orange whi le your eyes were c losed so that
when you opened your eyes they now appeared to the r ight o f
fixation, the fruit wo uld b e seen by the left brain. Tha t wo uld
present no problem for the normal brain. Surely the reader
would still know what to do, since the band of f ibers that
connects the two hemispheres i s st i l l in place . Yet , the animal
experiments suggested that if the neural interconnections between
the two half-brains were cut, the left brain would not know what
^ to do . This seemed un bel ievable , and in fact no one bel ieved it .
Our everyday sense o f what consc ious unity i s a l l about i s so
strong we would tend to reject such a c la im.
There was a way to test i t. I t so happ ened that back in 1940
a neurosurgeon in Rochester , New York, by the name of Wil l iam
Van Wagenen had sect ioned the neura l connect ions between the
two hemispheres in twenty-six epi lept ic pat ients . Epi lepsy occurs
in many kinds and degrees , and i t i s commonly managed with
ant iconvulsant medicat ions. When medicat ions fa i l to contro l
it , epilepsy can frequently be brought under control by surgical
removal o f the bra in t i ssue that i s malfunct ioning and tr igger ing
the seizures. In order for this procedure to work without causing
more problems than i t cures , the diseased area , or focus, has to
be localized to a particular point in the brain, and that point
cannot be in a crucial brain area such as the major language
area. Since the focus is frequently not in a crit ical area, surgical
removal can take place and the se izures contro l led. But i f the
focus is in the language area, or if there are several foci, this
method o f medica l re l ie f i s not possible; in such cases , spl i t -
brain surgery is considered.
In split-brain surgery, the corpus callosum is sectioned in
either one or two stages. In the initial surgeries carried out by
Van Wagenen, the anter ior commissure was somet imes sect ioned
as well. The initial idea of the surgery was that by disconnecting
the two half-brains, seizure activity initiated in one hemisphere
3
2
S p l i t - B r a i n S t u d i e s : T h e E a r l y Y e a r s
would not spread to the other, thereby leaving one half-brain
seizure-free and in control of the body.
These patients were observed at the t ime of their surgeries by
a ta lented young neuro log ist , Andrew Akela i t i s .
3
In a series of
studies, Dr. Akelaitis reported that the patients seemed essentially
normal or unchanged. Cutting the largest f iber tract in the brain
appeared to create in humans no problems of integration between
the two hemispheres. In fact, it was partly Akelaitis's studies Jf
that led Karl Lashley, the great neuropsychologist , to conclude
that the most important aspect of brain organization was the
overall amount of brain tissue present, not the specific areas.
Cutting the brain interconnections and finding no change in
function was about the biggest result for human clinical neurology
in those days. *
f
But something just didn't f i t . The result s o f the animal work
were clear, and though contrary, the Akelaitis work seemed just
as clear. As I sat in freezing Hanover that last winter, I thought
i t would be a good idea to go test the Rochester pat ients . We
had a l l ta lked about the pat ients during the preceding summer,
and no one could figure out why the results were not like those
seen in the animal studies . Were humans di f ferent or was the
original testing flawed in some systematic way? I wrote to Sperry
with some test ing ideas invo lv ing Po laro id lenses and tachisto -
scopes. The problem was that in order to test the patients
correctly, information presented to either the left or right of
fixation had to be quick-flashed. A tach istoscop e does just that.
Sperry wrote back and said he liked the idea, made some
suggestions, and wished me luck. I applied for a small grant
from the Mary Hitchcock Foundat ion a t the co l lege to cover
travel expenses during my stay in Rochester over the spring
break and got one hundred do l lars . A fr iend o f mine was go ing
to put me up so the money went straight to Hertz.
Everyone knew about the pat ients but no one had got ten
around to actua l ly test ing them. Akela i t i s had died as a young
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man an d Van Wagen en had m oved to Flor ida , so I was referred
to another neurosurgeon. Wh en I ta lked to him o n the ph one
from Hanover he was cordia l and recept ive . He to ld me he had
most of the patients' records and that by going through them I
should be able to get names, addresses, and so on. I was to go
to his office when I got to town and go to work.
After much preparation, I loaded the tachistoscopes, tape
recorder, and other baggage, all borrowed from the psychology
department of Dartmouth, into my rented car and took off . I
was nervous about the whole thing .
I arrived in Rochester and went straight to the doctor's office.
He was out, so his nurse directed me to the records and said I
was to start. I took a stack of folders and began, trying to cut
through a lo t o f what to me seemed l ike mumbo jumbo. After
a couple o f hours the phone rang . It was the neurosurgeon
ca l l ing to te l l me he had changed his mind and that I couldn't
carry out the studies after all. I was f labbergasted. He gave no
real reason but added, "You know I was a resident at the t ime
those surgeries were carried out and, if you ask me, the callosum
was rarely if ever fully sectioned."
I wrote Sperry the bad news, put away my gear, and played
al l spr ing . When I arr ived in Pasadena in June, I knew imme
diately that I was in the right place. Many of the friends I had
made the preceding summer were still there. I felt the added
excitement o f start ing on a new adventure and the matter-o f -
fact curiosi ty o f whether or not I could cope with the Caltech
curriculum. I was appropria te ly n ervous bu t nonetheless st il l
sort o f cocky . My f irst two years a t Dartmouth were rocky t imes
for me, and my "buco l ic" Cal i fornia high schoo l educat ion
wasn't behind me unt i l the start o f my junior year . At this po int
I felt I had a good Ivy League education and that once learning
how to learn was in hand, the rest would be easyor so I
thought .
In order to qualify for a Ph.D. in biology one had to take an
ora l exam in zoo logy . I had just f inished m y comp rehens ive
3 4
S p l i t - B r a i n S t u d i e s : T h e E a r l y Y e a r s
3 5
exams in zoo logy a t Dartmouth and had done wel l , so I asked
Sperry if I could take the test at the end of the summer and get
it out of the way. He agreed and I prepared for a late summer
exam to be g iven by Sperry and A. H. Sturdevant , the famous
and very senior geneticist . I checked with the other graduate
students about the test , and they told me Sturdevant had several
boxes o f insects he lent out for studyon the exam he gave a
test box of f ifty insects to identify by both genus and species. So
I trotted up to his office, got the boxes, and retired to my office
to study them.
The exam took place one a f ternoon in Sturdevant 's o f f ice . He
was an avuncular sort , a lways smoking a pipe . He led o f f the
quest ioning and sure enough the f irst thing he asked me to do
was identify a box of f ifty insects. I got forty-nine out of the f ifty
correct. He smiled, asked me a couple of other perfunctory
quest ions, and then passed the quest ioning over to Sperry .
Sperry , who a lways adopts a sto ic posture in this kind o f
s i tuat ion, started o f f with the s implest quest ion in embryology ,
one any undergraduate knows the answer to . He asked me to
descr ibe the development o f the o t ic capsule , that i s , the devel
opment o f the inner ear . A piece o f cake , I thought to
myself,
and started in. Sperry gave me no feedback. He just sat there
and l i stened to my answer. There were no "Uh-huhs" or "yea ,
yea, yeas," no sign I was on the right track. I panicked. What
the old otic capsule did in its proper migration to the correct
part of the brain was to take a left turn, change its basic
composit ion, and wind up, I think, in the l iver . But a f ter my
answer they would have bet I couldn't recognize a frog if it had
jumped up on the table . They asked me to step out o f the room
and a few minutes la ter Sperry came out to say they thought I
ought to take the exam over in the fall after school started. I
was crest fa l len but wiser . So much for the Ivy LeagueCaltech
would require my total energies.
Roger W . Sperry was forty-eight years old when I arrived. H e
had already survived a major medical incident, a bout with
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3 7
tuberculosis. Sperry was considered a complex figure, painfully
shy and incessant ly wondering what mot ivated people 's act ions.
He was considered a l oof by his peers , yet was ent ire ly approach
able by his students. Prior to his arrival at Caltech in the early
1950s at the insistence of Nobel laureate George Beadle, who
accurate ly perce ived his genius, Sperry had held som e secondary
posi t ions in the academic world. Except perhaps for Sir John
Eccles , Roger Sperry was far and away the most famous bra in
scientist living at the t ime. As a result of his revolutionary
studies on nerve specificity, he was considered one of the primary
thinkers in neurobio logy . The data-driven theory he out l ined in
the 1950s st i l l guides a huge amount o f current research in
neurobio logy . He had a lso conducted a ser ies o f experiments
set t ing l imits on runaway theories about the underly ing bio logy
of Gesta l t pr inciples . And he had been working on the spl i t -
brain preparation for approximately eight years. He was an
inst i tut ion in his own t ime.
Meanwhile the real business I was interested in had already
started. Shortly after I arrived, Sperry called me in to say that
Joseph Bogen, a neurosurg ica l resident a t the White Memoria l
Hospital, was planning to do split-brain surgery on humans late
that fall. Bogen had been at Caltech on a postdoctoral fellowship
with Professor Anthony Van Harreveld whose o f f ice was next to
Sperry's. Bogen had become interested in the split-brain issue
and wanted to see whether or not the surgery made sense for
the contro l o f epi lepsy in humans. The ear l ier reports by Van
Wagenen and Akela i t i s were a lways quoted as showing the
seizure-co ntrol aspect of the surgery to be incon sequ ential. Bogen
dug out a l l the papers and began try ing to check out this
assertion. He discovered that when all the case histories were
sorted out , there was just as much ev idence conf irming contro l
as there was for nonconf irmat ion. Bogen thought the surgery
worth a try , especia l ly on a pat ient who could not be contro l led
through normal ant iconvulsant medicat ion. Case W.J . was the
first patient.
Since I had already developed some tests for the Rochester
expe rime nts an d since I was just starting out, Sperry thought I
was a good choice to head the project. There were others around
who could have done the work but they were either leaving or
uninterested. Mitchell Glickstein had tried his luck on a girl
who had been referred to the lab with a suspected callosal lesion.
The test ing proved impossible and he dec ided he l iked monkeys
better, so the project fell straight into my lap.
One o f the things that made Sperry an exce l lent mentor was
that he left you alone. He set a laboratory context for work, and
he was always there working to make things better, to advise, to
assist , and to guide. But he didn't order anyone around or tell
anyone what to do . Many senior sc ient ist s do not operate the ir
labs that way: graduate students are pawns for their chess games.
Not Sperry , and because o f that everybody benef i tedSperry as
much as his students. As a result , everything that came out of
the work was a real team effort. We all freely interacted and
talked all the t ime about everything. In the early years the work
was being done primari ly by Sperry , Bogen, and
mysilf,
but
others were around too .
In the ear ly 1960s, when a l l o f this was go ing on, there was a
special atmosphere at Caltech. For the f irst year I lived in a
house across the street from the bio logy labs, which was whim
sically listed in the local phone book as J. A. Prufrock. Charles
Hamilton, another student of Sperry's, arranged that I got a
room there, right across the hall from his. Five people were
living in the house at the t ime, including two theoretical physicists
who have gone on to great things.
Sidney Cole man , then a student o f the great Richard Fe ynm an
and now a professor of theoretical physics at Harvard, lived
down the ha l l . His work habit s were as odd as mine . At one
point I used to get up a t midnight and go to the lab unt i l about
four in the morning , come back for a break, and then go back
to the lab unt i l about s ix in the evening . One morning I came
back about four and Coleman's l ight was on. There he was ly ing