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Mysteries of Consciousness

Growing New Brain Cells

What Dreams Mean

The Mind-Body Connection

Sex and the Brain

Origins of Emotions

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Mysteries of Consciousness

Growing New Brain Cells

What Dreams Mean

The Mind-Body Connection

Sex and the Brain

Origins of Emotions

letter from the editor

on our minds

Mankind will possess incalculable advantages and extraordinary con-

trol over human behavior when the scientiﬁc investigator will be able

to subject his fellow men to the same external analysis he would em-

ploy for any natural object, and when the human mind will contem-

plate itself not from within but from without.

Established 1845

The Hidden Mind is published by

the staff of SCIENTIFIC AMERICAN,

with project management by:

EDITOR IN CHIEF: John Rennie

EXECUTIVE EDITOR: Mariette DiChristina

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Ivan Petrovich Pavlov’s observation , penned in 1910, was prescient. Still,

he was far from the ﬁrst to speculate about such “incalculable advantages” —

from the practical, such as new medical treatments, to the more lofty con-

cerns of why we are as we are. These questions may go back to the dawn of

human self-awareness.

Weighing just three pounds and en-

compassing some 100 billion neurons,

the brain is the most complex organ in

the human body. It and the spinal cord

supervise all physical operations. And yet

it has proved to be a most elusive organ,

hiding the inner workings of the mind,

which deﬁnes and creates our unique per-

sonalities, intellect and consciousness.

During the 1990s — dubbed the “de-

cade of the brain” by presidential decree —

scientists unraveled more about the brain’s

intricate, interconnected cascade of elec-

trical impulses and chemical processes

than would even have seemed possible to

many psychologists and neuroscientists just a few decades ago. These discov-

eries, which are proceeding at a rapid pace, could revolutionize treatments of

various brain disorders. For example, researchers are trying to coax stem cells

to regenerate areas of the brain damaged by stroke, injury or diseases such as

Alzheimer’s and Parkinson’s. Advances in the understanding of brain struc-

ture, chemistry and function have placed this and other novel treatments with-

in reach. Scientists have also mapped much of the elaborate geography of the

brain and traced its sensory pathways. They have identiﬁed how the brain uses

discrete systems for various types of learning and found where and how mem-

ories are stored. They have explained much about the nature of dreams, emo-

tions and the conscious mind.

The latest developments in these areas and more are addressed in this spe-

cial edition from Scientiﬁc American . The Hidden Mind brings together and

updates ﬁrsthand reports from some of the ﬁnest minds exploring the brain

today. We welcome you to join us as we continue the age-old quest to un-

derstand our minds and ourselves.

John Rennie

Editor in Chief

Scientiﬁc American

editors@sciam.com

www.sciam.com

THE HIDDEN MIND 1

MAGNETIC RESONANCE imaging

( shown ) and other techniques can

reveal much about structures of the

brain, yet the nature of our minds

remains elusive.

the hidden

Volume 12 Number 1 mind

2002

mind

SCIENTIFIC AMERICAN

letter from the editor

how the brain creates the mind

BY ANTONIO R. DAMASIO

We have long wondered how the conscious mind

comes to be. Greater understanding of brain function

ought to provide an eventual solution.

the problem of consciousness

BY FRANCIS CRICK AND CHRISTOF KOCH

It is now being explored through the visual system —

requiring a close collaboration among psychologists,

neuroscientists and theorists.

on consciousness

BY NIKOS K. LOGOTHETIS

In their search for the mind, scientists are focusing on visual

perception — how we interpret what we see.

the split brain revisited

BY MICHAEL S. GAZZANIGA

Groundbreaking work over four decades has produced ongoing

insights about brain organization and consciousness.

sex differences in the brain

BY DOREEN KIMURA

Men and women display patterns of behavioral and

cognitive differences that reﬂect varying hormonal inﬂuences

on brain development.

for the adult brain

BY GERD KEMPERMANN AND FRED H. GAGE

Contrary to dogma, the human brain does produce

new nerve cells in adulthood. Can this capacity lead

to better treatments for neurological diseases?

2 SCIENTIFIC AMERICAN

contents

vision: a window

new nerve cells

sign language in the brain

BY GREGORY HICKOK, URSULA BELLUGI

AND EDWARD S. KLIMA

How does the human brain process language?

Studies of deaf signers hint at an answer.

the meaning of dreams

BY JONATHAN WINSON

Dreams may be crucial in mammalian memory processing.

Important information acquired while awake may be

reprocessed during sleep.

emotion, memory and the brain

BY JOSEPH E. L E DOUX

The neural routes underlying the formation of memories about

primitive emotional experiences, such as fear, have been traced.

the neurobiology of fear

BY NED H. KALIN

Researchers are teasing apart the neurochemical mechanisms

that give rise to various fears in monkeys. The results could lead

to new ways to treat anxiety in humans.

in disease

BY ESTHER M. STERNBERG AND PHILIP W. GOLD

The brain and the immune system continuously signal each other,

often along the same pathways, which could explain how

state of mind inﬂuences health.

experience

BY DAVID J. CHALMERS

We are at last plumbing one of the most profound mysteries

of existence. But knowledge of the brain alone may not get

to the bottom of it.

Cover illustration by Melissa Szalkowski

Scientific American Special (ISSN 1048-0943), Volume 12, Number 1, 2002, published by Scientific

photographic or electronic process, or in the form of a phonographic recording, nor may it be stored

in a retrieval system, transmitted or otherwise copied for public or private use without written

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THE HIDDEN MIND 3

the mind-body interaction

the puzzle of conscious

Brain

We have long wondered

how the conscious mind

comes to be. Greater

understanding of brain

function ought to lead

to an eventual solution

Creates

the

Mind

By Antonio R. Damasio

At the start of the new millennium, it is apparent that one question towers above all

others in life sciences: How does the set of processes we call

mind emerge from the activity of the organ we call brain? The

question is hardly new. It has been formulated in one way or

another for centuries. Once it became possible to pose the ques-

tion and not be burned at the stake, it has been asked openly

and insistently. Recently the question has preoccupied both the

experts — neuroscientists, cognitive scientists and philoso-

phers — and others who wonder about the origin of the mind,

speciﬁcally the conscious mind.

The question of consciousness now occupies center stage

because biology in general and neuroscience in particular have

been so remarkably successful at unraveling a great many of

life’s secrets. More may have been learned about the brain and

the mind in the 1990s — the so-called decade of the brain — than

during the entire previous history of psychology and neuro-

science. Elucidating the neurobiological basis of the conscious

mind — a version of the classic mind-body problem — has be-

come almost a residual challenge.

Contemplation of the mind may induce timidity in the con-

templator, especially when consciousness becomes the focus of

the inquiry. Some thinkers, expert and amateur alike, believe

the question may be unanswerable in principle. For others, the

relentless and exponential increase in new knowledge may give

rise to a vertiginous feeling that no problem can resist the as-

sault of science if only the theory is right and the techniques are

powerful enough. The debate is intriguing and even unexpect-

ed, as no comparable doubts have been raised over the likeli-

hood of explaining how the brain is responsible for processes

such as vision or memory, which are obvious components of

the larger process of the conscious mind.

I am ﬁrmly in the conﬁdent camp: a substantial explanation

for the mind’s emergence from the brain will be produced and

perhaps soon. The giddy feeling, however, is tempered by the

acknowledgment of some sobering difﬁculties.

Nothing is more familiar than the mind. Yet the pilgrim in

search of the sources and mechanisms behind the mind em-

barks on a journey into a strange and exotic landscape. In no

particular order, what follows are the main problems facing

those who seek the biological basis for the conscious mind.

The ﬁrst quandary involves the perspective one must adopt

to study the conscious mind in relation to the brain in which we

believe it originates. Anyone’s body and brain are observable

to third parties; the mind, though, is observable only to its own-

er. Multiple individuals confronted with the same body or brain

can make the same observations of that body or brain, but no

comparable direct third-person observation is possible for any-

one’s mind. The body and its brain are public, exposed, exter-

nal and unequivocally objective entities. The mind is a private,

hidden, internal, unequivocally subjective entity.

How and where then does the dependence of a ﬁrst-person

mind on a third-person body occur precisely? Techniques used

to study the brain include reﬁned brain scans and the measure-

ment of patterns of activity in the brain’s neurons. The naysay-

ers argue that the exhaustive compilation of all these data adds

up to correlates of mental states but nothing resembling an ac-

tual mental state. For them, detailed observation of living mat-

ter thus leads not to mind but simply to the details of living mat-

MULTIMEDIA MIND-SHOW occurs constantly as the brain processes external

and internal sensory events. As the brain answers the unasked question of

who is experiencing the mind-show, the sense of self emerges.

4 SCIENTIFIC AMERICAN

Updated from the December 1999 issue

How

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