pm michaell gazzaniga the social brain

7/26/2019 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

ix


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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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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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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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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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12


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


13/116


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


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

15


14/116


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.


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

6


15/116


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


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

9


16/116


20


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


17/116


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


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


18/116


24


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


19/116


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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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


22/116


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


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


23/116


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


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


24/116


3 6


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

pm michaell gazzaniga the social brain

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