scientific american - 1994 04 - the dilemmas of prostate cancer

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APRIL 1994

$3.95

Ancient Peruvian mask and headdress offer clues about a mysterious pre-Incan civilization.

The dilemmas of prostate cancer.

The real culprit in U.S economic ills.

Watching the Mind at work.

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April 1994 Volume 270 Number 4

44

50

58

66

Trade, Jobs and Wages

Paul R Krugman and Robert Z Lawrence

Charge and Spin Density Waves

Stuart Brown and George GrŸner

Visualizing the Mind

Marcus E Raichle

4

Marc B Garnick

Chemistry and Physics in the Kitchen

Nicholas Kurti and HervŽ This-Benckhard

The sources of U.S economic malaise are here, not abroad Manufacturing as apercentage of GDP declines because consumers are buying more services andfewer goods Manufacturing jobs vanish because machines replace workers; wagesstagnate because productivity has slowed These trends would persist even in theabsence of foreign competition and the rise of a global economy

In certain metals the lattice can aÝect the charge or spin of the electrons so thatthe particles organize themselves into crystalline arrays When voltage is applied,the electrons, like the members of a marching band, all move together, maintain-ing their relative positions Such systems provide an opportunity to study self-organized criticality, which is also evidenced in earthquakes and avalanches

In the hands of neurobiologists, MRI and PET imaging are revealing the ical processes in the brain that underlie the mind Monitored by scanning devices,subjects recall a word or generate a verb As they perform such tasks, the ßow ofblood to various parts of the brain changes as each becomes engaged The re-search presents some of the Þrst images of the human mind at work

physiolog-Cuisine, haute and bas, has evolved for centuries in the form of an ephemeral art.

Yet the materials are humble biological ones that respond in predictable ways toone another and to changes in temperature and pressure as time passes Whyshould not the knowledge embodied in chemistry and physics be brought intothe kitchen, where it can serve instinct and inspiration?

A common cause of death among men, this cancer has been detected with creasing frequency in recent years Questions about the eÝectiveness of therapycloud decisions about treating the illness Older patients, if left untreated forsmall tumors, may die of other causes But even if treatment is curative, manymenÑyoung and oldÑface impotence and incontinence as a result of therapy

in-PROSTATE

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90

98

The Pioneer Mission to Venus

Janet G Luhmann, James B Pollack and Lawrence Colin

Science and the Citizen

Science and Business

Book ReviewsThreads of the urban fabric Art

of hard copy Star photographer.Essay:Anne Eisenberg

Emoticons and other artifacts

of the new Epistolary Age

The Amateur ScientistProfessor Kurti and MonsieurThis present the scientiÞc souÜŽ

T RENDS IN BIOLOGICAL RESTORATION

Nurturing Nature

Marguerite Holloway,staÝ writer

Precious Metal Objects of the Middle Sic‡n

Izumi Shimada and Jo Ann GriÛn

a retrieval system, transmitted or otherwise copied for public or private use without written permission of the publisher Second-class postage paid at New York, N.Y., and at additional mailing offices Canada Post International Publications Mail (Canadian Distribution) Sales Agreement No 242764 Canadian GST No R 127387652 Subscription rates: one year $36 (out- side U.S and possessions add $11 per year for postage) Subscription inquiries: U.S and Canada (800 ) 333-1199; other (515) 247-7631 Postmaster : Send address changes to Scientific American, Box 3187, Harlan, Iowa 51537 Reprints available: write Reprint Department, Scientific American, Inc., 415 Madison Avenue, New York, N.Y 10017-1111, or fax : (212) 355-0408.

Two aspects separate this Þeldwork from other studies of the Sic‡n in Peru: thetomb had not been plundered, and an experienced goldsmith was among theworkers As a result, the Þnd sheds clear light on a great native American culture,and the techniques used by the Sic‡n masters have deftly been reconstructed

Over 14 years, the multiple components of Pioneer Venus gathered vast stores of

information about our sister planet Engineering resourcefulness came togetherwith scientiÞc creativity in a synergy that lifted understanding of Venus in partic-ular and planetary physics in general to unexcelled levels of sophistication

FloridaÕs Everglades are serving as testing groundĐand battleÞeldĐfor an epicattempt to restore an environment damaged by human activity As conservation-ists, oÛcials and commercial interests square oÝ, the practitioners of theßedgling technology of biological restoration attempt to bring back a woundedecology Can they succeed here or elsewhere? How can success be measured?

Perry for Defense Epidemic endometriosis Bang! YouÕrealive Quantum computer

Hedgehog genes Pinning theflux ScientiÞc silliness

PROFILE: Edward O Wilson revisitssociobiology

Japan Inc.Õs listening posts

Texas Instruments does it withmirrors Softwars Cheap solarcells Architecture that shakesquakes THE ANALYTICAL ECONOMIST: Hospital proÞts continue to cool

14

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44Ð45 AP/World Wide Photos

46 Culver Pictures, Inc (top ),

51 Robert V Coleman and

C Gray Slough, University

of Virginia

52Ð55 Jared Schneidman/Jared

Schneidman Design

56 Jared Schneidman /JSD

(top ), Comstock, Inc./

Georg Gerster (bottom)

58Ð59 Jonathan D Cohen,

Car-negie Mellon University

60Ð62 Marcus E Raichle

63 Guilbert Gates

64 Rodolfo R Llinas, New

York University Medical

Center

66Ð67 Steve Murez/Black Star

68 Andrew Paul Leonard/APL

Microscopic (left ), Dana

83 Yutaka Yoshii (photograph )

84 Izumi Shimada (left, top

right and bottom right ),

Yutaka Yoshii (center right )

85 Izumi Shimada

86 Yutaka Yoshii (top ),

Jo Ann GriÛn (bottom )

87 CŽsar Samill‡n (drawing ),

Jo Ann GriÛn (top right and bottom ), Yutaka Yoshii (middle )

88 Yutaka Yoshii (top ),

Izumi Shimada (bottom )

89 Yutaka Yoshii

91 George Retseck

92 National Aeronautics and

Space Administration (top ), Tomo Narashima (bottom)

93 NASA (left), Jared

Schneidman/JSD (right )

94 Tomo Narashima

95 A.I.F Stewart, University

of Colorado96Ð97 Tomo Narashima98Ð99 Marguerite Holloway

100 Johnny Johnson (top ),

106 Andre F Clewell, Hall

Branch Restoration Project

108 Ken Sherman120Ð123 Kathy Konkle

THE ILLUSTRATIONS

Cover photograph by Yutaka Yoshii

THE COVER photograph shows for the Þrsttime a recently reassembled Sic‡n mask andheaddress Because of extensive looting ofthe Sic‡n tombs, no other assemblage ofthis type is known to have survived themelting-pot fate of most of the stolen arti-facts The Sic‡ns ßourished before the Incas,from A.D 700 to 1300, in northern Peru

They produced huge numbers of gold jects, many showing remarkable technologi-cal and aesthetic sophistication (see ỊPre-cious Metal Objects of the Middle Sic‡n,Ĩ byIzumi Shimada and Jo Ann GriÛn, page 82)

¨

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LETTERS TO THE EDITORS

Science Marches On

I am requesting that you attempt the

following experiment You will need the

cooperation of a whole town of people

Have everybody remove their wedding

rings I would be interested in what

hap-pens to human sexuality and

reproduc-tion when nobody wears a ring

You might be inclined to respond that

nothing would happen But gold is an

unusual element in terms of electron

conductivity, and the ring, because of

the bipedal form of humans, is in close

proximity to the sex organs

GEORGE SILIS

Cleveland, Ohio

My theory, and I will oÝer proof, is

that the late, great Howard Hughes was

a time traveler Every business venture

that Mr Hughes undertook involved

high technology and advanced

applica-tions Where did he get his insight? The

answer : from the future! Why was Mr

Hughes such a recluse? The answer : he

was back from the future and did not

want to be revealed

CHRISTOPHER J RONAN

U.S Air Force

For some time, I have been chagrined

at the bumbling of physicists The

en-tire Þeld needs a new beginning I can

oÝer the following help : Space has no

dimensions and no fabric Space cannot

be warped Space is a state of

nothing-ness I repeat, space cannot be warped

My girlfriend says you guys are going

to pass this around, saying, ÒHey,

Char-lie, check out this quack.Ó

JOHN NICHOLS

Carson, Calif

The names of most scientiÞc

disci-plines end in the suÛx Ò-ology.Ó I

pro-pose a new name for those amazing bits

of discovery to which we react by

say-ing, ÒWow!Ó We could call it bygology

DONALD M SWAN

Old Saybrook, Conn

NO! You havenÕt heard from me, and

you shall not until you have signed a

contract The cost to ScientiÞc

Ameri-can is now $1.00 per character space

for any article For more than 25 years,

I have sent articles to you, all of which

were rejected The Grand UniÞed Field

is now wide open The ancient matics has been recovered, and I can-not tell you how amazing it is It de-pends entirely on prime numbers, ofwhich you have not the slightest com-prehension There is no need for trigo-nometry or calculus They are now dead

mathe-subjects (as dead as ScientiÞc

Ameri-can is going to be)

Be sure to include a retainer check inyour next letter

BEN IVERSONTigard, Ore

Something We Said?

Cancel my subscription at once

I thought you might have changed

But you never do, do you? Is there noend to your Stalinist suckups? Of coursenot Whether it is your sniÝ-and-sneerapproach to reporting economics oryour toadying to the eco-statist line,the garbage never stops In the name ofscience, you commit these abomina-tions every issue without fail You arethe damned of the earth Yours is theguilt beyond forgiveness

JOHN L QUELBellevue, Wash

Thanks to ÒRed-Banner Burger,Ó byGary Stix [ÒScience and Business,Ó SCI-ENTIFIC AMERICAN, June 1993], I amup-to-date on your attempts to restrict

me to a Òchoice of a hamburger welldone or just plain burned.Ó You couldnot have made it any more clear thatyour objective is to kill your readers

I sincerely hope you and your

associ-ates at ScientiÞc American will be

among the Þrst and most enthusiasticusers of the latest poisonous meatproductÑirradiated chickens I will bedelighted to dance at your funerals

ROBERT G HUENEMANN

La Honda, Calif

NobodyÕs Perfekt

The excellent article ÒCurrent Events,Ó

by Philip Yam [SCIENTIFIC AMERICAN,December 1993], mentions Òa two-horsepower motorÑstrong enough topower the cooling fan in a desktopcomputer.Ó Do desktop computers now

really need fans the size of those forcentral air conditioning?

ROBERT NEUBOLDYork Haven, Pa

The editors reply :

The fan also cools our more heated comparisons

over-Have you actually used ÒinputtedÓ asthe past tense of a verb? Yes, in thecaption of the Þgure on page 150 ofthe January issue I am upset I am ap-palled I am horriÞed

I am out putted

DAVID C CALHOUNSeattle, Wash

The illustration on page 98 of theFebruary issue says the strong forceÒcouples quarks to form proteins andneutrons.Ó Do you favor meat or dairyproducts as sources of quark proteins?

BRUCE C ALLENCleveland, Ohio

We prefer crow or, better still, ated chickens

irradi-As the coauthor of The Private Lives

of Albert Einstein, I would like to

dis-tance myself from Peter HighÞeld (norelation), who was portrayed as a tab-loid hack in ÒKeyhole View of a Ge-nius,Ó by Fred Guterl [ÒProÞle,Ó SCIEN-TIFIC AMERICAN, January] If Paul Car-ter and I had wanted to put Einstein inthe worst possible light, we would nothave sent the draft manuscript to threeEinstein scholars and EinsteinÕs grand-daughter We do not in any way suggestthere were Òshades of Woody AllenÓ inEinsteinÕs relationship with his step-daughter! I remain conÞdent that ourbook contains the most authentic de-piction of Einstein the man, thanks toour use of more than 1,100 referencesand the kind help we received from theEinstein Papers Project at Boston Uni-versity and Evelyn Einstein

ROGER HIGHFIELD

The Daily Telegraph

London, England

Dr HighÞeld is correct : his name isRoger

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50 AND 100 YEARS AGO

APRIL 1944

ỊIn seven years the Armour

Founda-tion has grown from a name and a

good idea into one of the most

impor-tant institutions of its kind in the

Unit-ed States The Ơgood ideaÕ was to

pro-vide an industrial research service for

the particular beneÞt of small business

Today the foundation is 100 percent

devoted to war products But its

direc-tor is free to make some predictions

about the future One of these concerns

Ơradio cookery,Õ an outgrowth of

dia-thermy and ƠartiÞcial feverÕ treatment

He prophesies that we shall have

elec-tronic cooking as a generally accepted

commercial practice, but doubts its use

in the home because of the hazard of

high voltage One commercial

compa-ny has already perfected a thermal

ra-dio hamburger and hot-dog vending

machine The customer drops a coin

into a slot, and after half a minute a

ra-dio-cooked morsel pops out.Ĩ

ỊRecently, Dr James Hillier of RCA

Laboratories announced the

prelimi-nary development of a fundamental

tool to which he gave the name

elec-tron microanalyzer Its function, he

said, was the elemental analysis of

ex-tremely small areas within electron

mi-croscope specimens With this

instru-ment, the user can study a specimen

already so microscopic that it must be

magniÞed thousands of times in order

that its details may be seen at all It is

possible to select one local area or haps a particle no larger than 1/100,000inch in diameter and as small in weight

per-as 1/1,000,000,000,000,000gram, and mine exactly which chemical elementsthat one sub-microscopic area or parti-cle contains.Ĩ

deter-ỊAlthough the war has been sible for many new inventions, it hasadded little to the worldÕs store of fun-damental knowledge, Dr Frank B Jew-ett, vice-president of the American Tele-phone and Telegraph Company, recent-

respon-ly told members of the New YorkUniversity Institute on Post-War Recon-struction Progress in certain Þelds ofscientiÞc knowledge, he said, has beenoÝset by a virtual cessation of researchwork in others that are not consideredessential to the war eÝort.Ĩ

APRIL 1894ỊThe use of electricity for householdpurposes has hardly got beyond the ex-perimental stage, save in the depart-ment of lighting; but enough has beendone to show what a transformationmay be worked when it is possible tohave houses heated by it Then the mereturning of a switch will suÛce With re-gard to cooking, there are numerousappliances already devised, and only

waiting for the cheapening of the rent to be widely taken advantage of ANew York lady is said to have so con-trived matters that she can, before get-ting out of bed, start a Þre in the kitch-

cur-en by turning on the currcur-ent; and whcur-enshe comes downstairs Þnds the ket-tle boiling and the place comfortably

warmed.ĐChambersÕs Journal.Ĩ

ỊMr Lester Ward, in a lecture

recent-ly delivered before the AnthropologicalSociety of Washington, showed that thework of Ramon y Cajal and others indi-cated that protoplasm is not merely thephysical basis of life, but is the physi-cal basis of mind also In his words, Ơtheprevailing fashion among scientiÞc men

of emphasizing the mystery of mind isunnecessary and illogical, since mind is

no more a mystery than matter.Õ ĨỊDr J M Macfarlane has recently dis-covered that leaf blades of the Dion-

¾aĐthe Venus ßytrapĐwill not spond to a single touch There must be

re-a second stimulus before re-an re-attempt re-atclosing is made But even here thestimuli must have an interlude of near-

ly a minute If the two stimuli followclosely, no response follows Here may

be the advantage of the interlude: it fers a way of discovering whether thatwhich alights on the leafÕs surface iseatable or not A piece of gravel mightreboundĐmight make two stimuli closeafter one another An insect would wait

of-a short time to collect its senses, of-andformulate some plan of escape beforestruggling to get free The discovery of

Dr Macfarlane is probably the mostwonderful of all wonderful things thathave been discovered in the behavior

of plants.ĐThe Independent.Ĩ

ỊThe Midwinter Fair, an internationalexhibition, opened on January 27, 1894,and occupies about 160 acres of Gold-

en Gate Park, San Francisco The ufactures and Liberal Arts Building,shown in the drawing, is probably theÞrst building to attract the eye Thegreat blue dome and golden lanternglistens against the intense blue of thesemitropical sky like an immense jew-

Man-el, while a peculiar suggestion of age isgiven by the grayish-green tiles of theroof This building is the largest struc-ture at the Fair In this great buildingthirty-eight nations have exhibits TheUnited States is well represented.Ĩ

The Manufactures and Liberal Arts Building at the Midwinter Fair

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Cool Man, Hot Job

William Perry takes on the

challenge of military reform

First Les Aspin buckled, then

Bob-by Inman blew up on takeoÝ

When the dust settled, there was

Bill Perry His initial demurrer

notwith-standing, the view inside the Beltway is

that this quiet-spoken technocrat,

schol-ar and businessman seems in some

im-portant ways to have emerged as

secre-tary of defense at just the right time

Although not given to

bull-in-the-woods bellowing, William J Perry has

for years been a tenacious advocate of

the electronic battleÞeld His original

rationale had more to do with

prevent-ing Soviet forces from overrunnprevent-ing their

numerically inferior NATO

counter-parts than with Þghting brushÞre wars

But high-technology weaponry used for

General H Norman SchwarzkopfÕs

Des-ert Storm permitted an intoxicating

(perhaps dangerously so) victory

That lesson of history will stand

Per-ry in good stead as he goes on point in

the corridors of power The

disappear-ance of the Soviet Union and its

satel-lites as credible military threats and the

consequent demand for a Òpeace

divi-dendÓ have led to steadily decreasing

defense expenditures in recent years

Budgets are down 35 percent in real

terms from their peak in 1985, and the

administrationÕs proposed defense

bud-get for 1995, at $263.7 billion,

contin-ues that trend But the research and

de-velopment component, at $39.5 billion,

represents a 4 percent increase Basic

research, which amounts to $1.23

bil-lion within that total, is also slated for

a small increase

Despite his studied blandness, Perry

will Þght hard for military research

This commitment has earned him the

respect of Pentagon brass, as well as of

defense contractors who are already

staggering from the impact of cutbacks

They are well aware that as

undersecre-tary of defense for research,

engineer-ing and acquisition under President

Jimmy Carter in the 1970s, Perry

cham-pioned stealth technologies and

preci-sion-guided munitions At the time,

many in the military favored matching

brute force with brute force

Not all PerryÕs technological Þxes

have been triumphs: his critics point

out that he gave the thumbs-up to theexpensive and controversial MX missile,

as well as to the canceled Aquila motely Piloted Vehicle Moreover, notesKosta Tsipis, a defense analyst at theMassachusetts Institute of Technology,the mild-mannered Perry lacks the po-litical clout he might need to defendbudgets in bruising cabinet battles

Re-Yet Perry enjoys the advantage ofknowing the defense business from theinside He prospered as the founder of

a defense electronics Þrm and as atechnology investment adviser ÒHe wasalways a believer in technological supe-riority,Ó Tsipis says ÒI think heÕll try tomaintain military research and devel-opment generally, but because of pres-sures on the budget heÕll put more intobasic research.Ó

Other defense analysts agree thatPerry will honor President Bill ClintonÕscommitment to a strong military bynurturing research that might yield thegame-changing technologies of nextcentury Research is much cheaper thanlate-stage weapons development Ad-

vances in computer simulation mean it

is now possible to learn a lot about theperformance of a weapon without go-ing to the expense of building it, notesAlbert R C Westwood, a researcher atSandia National Laboratories Perry wellunderstands the signiÞcance of thoseadvances, Westwood says Furthermore,Perry can be expected to support inter-national arms-control treaties as aneconomic route to military security.Perry has also taken it on himself toimprove eÛciency all round The De-partment of Defense, bowing to the in-evitable, is now reviewing the roles ofthe 68 laboratories that it runs, and theDepartment of Energy has impaneled ablue-ribbon commission to look intothe future of the national labs that itmaintains Undersecretary of Defensefor Acquisition and Technology John

M Deutch acknowledged at a recentconference that ÒsigniÞcant problemsÓmean the defense labs Òinevitably willhave to be downsized.Ó

Perry has other schemes in the works

to get the most bang for the research

SCIENCE AND THE CITIZEN

STEALTH MANDARIN: Secretary of Defense William J Perry will have to fight get pressures and bureaucracies to sustain research for the military of next century.

bud-14 SCIENTIFIC AMERICAN April 1994

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buck ỊPerry is a very innovative

think-er,Ĩ says Stanley V Jaskolski, chief

tech-nology oÛcer at Eaton Corporation

Jaskolski cites the example of Ịthe

Per-ry initiative,Ĩ a plan PerPer-ry started as

deputy secretary of defense last year

In essence, the initiative swaps U.S

wea-pons know-how for access to Japanese

technology Japanese manufacturers

are licensed to produce U.S.-designed

weapons that embody advanced

tech-nology in exchange for rights to

Jap-anese technologies that U.S companies

would like access to Something similar

Ịcould be done in other countries,Ĩ

Jas-kolski notes ỊIn principle, this could

be universally applied.Ĩ

The Perry initiative is a logical

exten-sion of his campaign to promote Ịdual

useĨ technologies, which can be

proÞt-able in both military and civilian

set-tings That program brings him

face-to-face with the most redoubtable dragon

in the PentagonÕs cave: the military

pro-curement system The heart of that

sys-tem is the Ịmilspec.Ĩ

Numerous commissions and reports

have stated the case for simplifying or

abolishing milspecs, the elaborately

de-tailed technical requirements that the

Pentagon habitually lays down for

pur-chases of everything from jet Þghters

to ashtrays Milspecs prevent the tagon from buying at civilian prices inthe civilian marketplace: they were re-sponsible for the celebrated $640 toiletseat and the $435 hammer Milspecsalso impede, Perry has said, the diÝu-sion of technologies resulting from mil-itary research into the private sector

Pen-In 1992 Perry chaired a task force ofthe Carnegie Commission on Science,Technology and Government, whose re-port makes his views clear The reportobserves that in 1991, 40 percent of themilitary acquisition budget was spent

on management and control personnel

In civilian commerce the equivalentÞgure is between 5 and 15 percent Thesolution that the task force advocated

is as simple as it is radical: ỊThe reform

of the defense acquisition system musthave as its principal thrust the integra-tion of the countryÕs defense industryand commercial industry to create asingle industrial base The critical ingre-dient of adaptation to commercial prac-tice is conversion from a regulation-based system to a market-based sys-tem.Ĩ Now Perry should be in a betterposition to achieve that conversion

Simplifying milspecs Ịis extremely

wiseĨ because such burdensome quirements often have the perverse ef-fect, according to Westwood, of delay-ing technological improvements West-wood was previously a vice presidentfor research and technology at MartinMarietta Aerospace, where he frequent-

re-ly encountered the problems milspecscreate Milspecs ỊdonÕt allow you to say

if thereÕs a better materialĐthey cutyou oÝ from real improvements,Ĩ West-wood complains

Moreover, PerryÕs credo of dual-usetechnology has become a buzzword indefense circles A trickle of defensecontractors starting to work on civilianprojects has become a ßood in the pastcouple of years, encouraged by defensedepartment programs that support suchshifts ỊWhat we need is a healthy man-ufacturing infrastructure that is convert-ible,Ĩ argues John Cassidy, vice presidentfor research at United Technologies.Few in Congress would disagree YetÞghts over which weapons systems tocancel and which industries to supportwill be bloody ỊPerry is going to be in

a very dynamic position to recraft themilitary of the future,Ĩ reßects one high-ranking congressional aide ỊItÕs going

to be a hot job.Ĩ ĐTim Beardsley

More than a decade ago a small group of physicists,

among them Richard P Feynman, began wondering

whether it would be possible to harness quantum effects

for computation Until recently, such investigations have

been highly abstract and mathematical Now Seth Lloyd, a

researcher at Los Alamos National Laboratory, has

pro-posed in Science how a so-called quantum computer

might actually be built

Lloyd points out that in one sense “everything,

includ-ing conventional computers, and you and me, is quantum

mechanical,” since all matter obeys the laws of physics

One feature distinguishing quantum computers from

con-ventional ones, Lloyd explains, is the way they store

in-formation Conventional computers use electrical charge

or its absence to represent 0’s or 1’s used in the binary

language of data storage

In a quantum machine, information would be

represent-ed by the energy levels of individual particles or clusters

of particles, which according to quantum mechanics

oc-cupy discrete states; the ground, or “down,” state could

signify a 0 and the excited, “up” state a 1 Lloyd says such

computers could be made out of materials with identical,

repeating units that behave quantum mechanically,

in-cluding long organic molecules, or polymers; arrays of

quantum dots, which are clusters of atoms with precisely

controllable electronic properties; and crystals

“Some-thing as simple as a salt crystal might do,” he states

Input is supplied by pulses of light or radio waves,

which would nudge the atoms, molecules or quantum

dots into energy levels representing, say, a particular

number More pulses of light would cause the system tocarry out a computation and disgorge an answer Becausequantum systems are notoriously susceptible to disrup-tion from external effects, an error-correction programwould monitor the progress of a computation and put itback on track when it goes awry

Such a computer would be much smaller and fasterthan any current model, Lloyd contends It could also per-form certain tasks beyond the range of any classical de-vice by exploiting a bizarre quantum effect known as su-perposition Under certain precisely controlled conditions,

a particle can briefly inhabit a “superposed” energy statethat is, in a sense, both down and up It has a 50–50 prob-ability of “collapsing” into one state or the other

Computers that can store information in a superposedform, Lloyd suggests, could generate truly random num-bers, a task that has proved fiendishly difficult for classi-cal computers They could thus solve certain problemswith a probabilistic element—such as those involvingquantum mechanics—more accurately than can conven-tional machines

Rolf Landauer of the IBM Thomas J Watson ResearchCenter, an authority on the limits of computing, has “anumber of reservations” regarding Lloyd’s scheme Lan-dauer argues, for example, that Lloyd’s error-correctionmethod will destroy the very superposition that he seeks(for reasons related to the fact that mere observation of aquantum system alters it) Yet Lloyd’s work is still “a stepforward,” Landauer says “He’s given us something toevaluate in more detail.” —John Horgan

Quantum Computing Creeps Closer to Reality

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20 SCIENTIFIC AMERICAN April 1994

Super Sonic

A gene named for a video

game guides development

The shape of a hand is as

comfort-ingly familiar as, well, the back of

oneÕs hand But to

developmen-tal biologists, it is also an enigma What

biochemical sculptor molds the delicate

embryonic tissues into limbs and

func-tioning organs during the Þrst weeks of

life? Researchers think they have

Þnal-ly found a famiÞnal-ly of genes that nudge

embryonic cells toward their proper

destiny One of these genes is a real

overachiever : in vertebrate organisms,

it organizes the central nervous system,

deÞnes the orientation of limbs and

speciÞes where Þngers and toes should

grow Its discoverers have

whimsical-lyÑand appropriatelyÑdubbed this

gene Sonic hedgehog, after the

hyper-active hero of a popular video game

CliÝ Tabin of Harvard Medical School,

Andrew P McMahon of Harvard

Univer-sity and Philip W Ingham of the

Impe-rial Cancer Research Fund in Oxford,

England, lead the three laboratories that

recently brought Sonic into the spotlight

through a set of papers in Cell Their

demonstration that Sonic induces

dra-matic changes in embryos, Tabin

ex-plains, Òopens the door ItÕs a great start

for looking at signaling events early in

embryogenesis.Ó

Before the advent of molecular

biolo-gy, embryologists usually resorted to

the Frankenstein-like measure of ting small bits of tissue out of embryosand grafting them into new positions

cut-to see what the results might be Crudethough those experiments might seemtoday, they yielded important clues

Workers found that during critical ods in development, some blocks ofcells organize extensive changes in theirneighbors For example, cells in thezone of polarizing activity ( ZPA ) alongthe posterior edge of a limb bud some-how dictate how the limb should be ori-ented and where digits should form

peri-Removing the ZPA prevents the limbfrom forming; moving the ZPA canchange the limbÕs orientation Embry-onic structures called the notochordand the neural ßoor plate were found

to serve a similar patterning function

in the development of the spine andcentral nervous system

Embryologists theorized that cells inthe ZPA and other patterning centersrelease a morphogen, or signaling mol-ecule Nearby cells presumably inter-preted the gradient of morphogen aspositional information and diÝerenti-ated accordingly For the past 20 years,much of developmental biology hasbeen a largely frustrating quest forthose morphogens ÒIn the whole ofvertebrate embryology, there isnÕt yet asingle unequivocally identiÞed morpho-gen,Ó notes Lewis Wolpert, a pioneer inthe study of limb development

Two years ago the cloning of a gene

called hedgehog in fruit ßies presented

a new opportunity Hedgehog takes its

name from the appearance of the tant ßies that lack it: they become short-lived embryos whose bottom surfacesare covered with spiky hairs Tabin, Mc-Mahon and Ingham decided indepen-dently to look for a similar gene in ver-tebrates but soon began collaborating.Using copies of the insect gene asprobes, the investigators found four re-

mu-lated hedgehog genes in vertebrates.

These genes appear to make a family ofstructurally unique signaling proteins.The researchers named three of thesegenes after species of living hedgehogs:

Desert, Indian and Moonrat.

But it is the fourth hedgehog gene,

Sonic, that has so far proved most

daz-zling In mice, chicks and zebraÞsh,cells in the ZPA, ßoor plate and noto-

chord activate Sonic at precisely the

times when they are shaping nearbystructures Moreover, when the research-ers inserted genetically engineered cells

that expressed Sonic into embryos, those

cells served as new patterning centers

As such, they could change the tion of limbs or create odd Òmirror im-ageÓ deformities ÒGenerally, you donÕtexpect to Þnd any single factor that me-diates several diÝerent important sig-naling interactions,Ó McMahon observes.ÒSo it was a big surprise.Ó

orienta-Tabin emphasizes that although

Son-ic protein is a primary developmentalsignal, it may not be a morphogen Òinthe classical sense.Ó No one yet knowswhether Sonic tells the limb bud how

to grow by diÝusing out of the ZPAand forming a concentration gradient.ÒIt could just as easily be somethingthat signals the adjacent set of cellsand starts a cascade of other informa-tion signals from them,Ó he explains.Tabin, McMahon and Ingham arenow looking for the receptor molecules

to which Sonic binds: the locations willclarify which cells are the direct targets

of the protein The workers are also interested in determining which Òup-

streamÓ signals tell cells to express

Son-ic And then there are the other hog genes to decipher : Desert seems

hedge-to limit its activity hedge-to the reproductivesystem, whereas early tests suggest

that Indian guides the diÝerentiation

of structures later in development.ÒExcitement!Ó is WolpertÕs reaction to

the hedgehog revelations More

thought-fully, he adds, ÒMy joke is that weshould enjoy it while we can We wentthrough a similar excitement for retino-

ic acid The history of these things isthat they turn out to be more compli-cated than one thinks.Ó So the current

success of Sonic hedgehog just kicks

the developmental problem up to anew level of diÛculty Game over? Not

by a long shot ÑJohn Rennie

MIRROR-IMAGE DEFORMITY involving the duplication of digits occurs in

embry-onic limbs that contain both a normal zone of polarizing activity ( ZPA ) and an

im-plant of cells expressing the patterning gene Sonic hedgehog

ALTERED CHICK WING

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Bang! YouÕre Alive

An unusual trio wins support

for ỊnonlethalĨ weapons

In weapons laboratories, the

Penta-gon and even the justice

depart-ment, a new buzzword is breeding :

nonlethality The basic idea is that

sol-diers and police, if only to maintain

good public relations, often want not

to kill their opponents but merely to

disable them or their weapons Bosnia,

Somalia and Waco come to mind

Of course, nonlethal weapons,

rang-ing from radar jammers to rubber

bul-lets, have long been in use Federal

re-searchers are now investigating a

broad-er array of devices These include lasbroad-er

rißes that temporarily blind the enemy

or his optical-sensing gear;

low-frequen-cy ỊinfrasoundĨ generators powerful

enough to trigger nausea or diarrhea;

explosives that emit

electronics-disrupt-ing pulses of electromagnetic radiation;

ỊstickumsĨ and Ịslickums,Ĩ chemicals

that make roads or runways

impass-ably gluey or slippery; and biological

agents that can chew up crops or other

strategic resources

Steven Aftergood of the Federation

of American Scientists, who has beentracking the nonlethal defense program,calls some of its components, and pro-ponents, Ịweird.Ĩ He notes that the pro-gram has been linked to nuclear wea-pons, which are hardly nonlethal, and

to Ịmind controlĨ devices; moreover,three of the most prominent advocates

of nonlethality share an interest in chic phenomena

psy-ỊEverything everyone says has to betreated with skepticism,Ĩ Aftergoodwarns But he adds, ỊThis is a real pro-gram Lots of money is being invested,mostly on a classiÞed basisĨ by the de-partments of energy and defense and,

to a lesser extent, the justice ment Aftergood has called for opening

depart-up the program to more public scrutiny

At a conference on nonlethality held

in Laurel, Md., last November, one ofthe few unclassiÞed talks was given byEdward Teller of Lawrence LivermoreNational Laboratory, who is known asthe father of the hydrogen bomb Tel-ler revealed that Livermore researcherswere studying the feasibility of a minia-ture rocket Ịguided so accurately that

it will ßy down the muzzle of a gun,make a little pop, destroy the gun, not

the gunner.ĨTeller urged that the non-lethality concept be stretched

a bit to accommodate Ịsmallnuclear explosivesĨ withyields equivalent to 100 tons

of conventional high sives, or roughly 1 percentthat of the bomb that de-stroyed Hiroshima With theseexplosives placed on ỊsmartĨrockets, the U.S could force,say, North Korea to shutdown its military facilities,Teller said ỊWe shall tell theenemy, the North Koreans,that if we Þnd that peoplecontinue to go into theseplaces, then at an unan-nounced moment they will

explo-be bomexplo-bed.Ĩ As long as theKoreans obey the U.S., in oth-

er words, the nuclear pons remain nonlethal

wea-The chairman of the ference was John B Alexan-der, who heads the nonle-thal defense program at Los

con-Alamos National Laboratory and hasbeen called (albeit by a publicist at LosAlamos) Ịthe father of nonlethal de-fense.Ĩ For these eÝorts, Alexanderwas recently honored as an ỊAerospace

LaureateĨ by the respected journal

Avi-ation Week & Space Technology The

citation did not mention that last yearAlexander organized a meeting onỊTreatment and Research of Experi-enced Anomalous Trauma,Ĩ at whichattendees discussed alien abductions,ritual abuse and near-death experiences.Alexander is a former U.S Army col-onel and self-described Ịhard-core mer-cenaryĨ with a doctorate in thanatolo-

gy, the study of death In 1980 he wrote

an article for a defense journal on sible military applications of psychicpowers He emphasizes that he does notthink paranormal techniques should bepart of the nonlethal program, becausesuch an association might be looked onaskance by funding agencies

pos-Two other advocates of nonlethality,Janet E Morris and her husband, Chris-topher C Morris, are science-Þctionwriters and self-educated national se-curity experts associated with the U.S.Global Strategy Council and the better-known Center for Strategic and Inter-national Studies, think tanks in Wash-ington, D.C Like Alexander, they haveshown an interest in paranormal phe-nomena, including remote viewing ( inwhich one supposedly ỊseesĨ distantscenes) and what they call Ịthe eÝect

of mind on probability.ĨThe Morrises have been involved inpromoting a Ịpsycho-correctionĨ tech-nology, developed by a Russian scien-tist, that is intended to inßuence sub-jects by means of subliminal messagesembedded in sound or in visual im-ages The Morrises say their intention

is not to make the device part of thenonlethal arsenal but to make the U.S.aware of its dangers so that counter-measures can be developed

Last year the Morrises organizedmeetings in which the technology wasdemonstrated for U.S scientists andoÛcials by its Russian inventor Ahealth oÛcial who observed the dem-onstration and requested anonymitydescribed the demonstration as Ịhocus-pocus,Ĩ adding that previous studieshave shown subliminal-suggestion tech-niques to be ineÝective Nevertheless,the Federal Bureau of Investigation re-portedly considered using the tech-nique to convince cult leader David Ko-resh to surrender before he and his fol-lowers were immolated last year

In the late 1980s Janet Morris was troduced to Alexander by a mutual ac-quaintance, Richard Groller, a formerintelligence oÛcer Morris, Alexander

in-STICKY FOAM engulfs a nequin in a test at Sandia National Laboratories Sticky- foam guns are among the nonlethal weapons being considered by the Department of Justice and other agencies.

Trang 11

10 percent of women in their ing yearsĐabout 5.5 million people inthe U.S and CanadaĐare being unrav-eled A report has linked the illness todioxin exposure; other research sug-gests that immune dysfunction plays arole ỊThis is a pivotal time for thestudy of endometriosis,Ĩ says Sherry E.Rier, an immunologist at the Universi-

childbear-ty of South Florida who led the teamthat conducted the work on dioxin.The discoveries coincide with the rec-ognition that the prevalence of endo-metriosis may be rising and becomingmore common in young women ỊThepublic health impact of this disease isenormous,Ĩ says JeÝ Boyd, a moleculargeneticist at the National Institute ofEnvironmental Health Sciences ỊIt af-fects millions and millions of people,but it does not garner the resources that

and Groller then teamed up to write

The WarriorÕs Edge: Front-Line gies for Victory on the Corporate Battle- Þeld Published in 1990, the book tells

Strate-corporate climbers how psychic powerscan help them rise to the top

Since then, the Morrises and der have had a falling-out, with eachside accusing the other of hogging cred-

Alexan-it for the concept of nonlethalAlexan-ity ander was ripping oÝ our ideas andsending them up the chain of com-mand,Ĩ Janet Morris says The Morrisesalso charge Alexander and other mili-tary oÛcials with trying to keep thenonlethal program under wraps byclassifying it

ỊAlex-Alexander acknowledges that manyaspects of nonlethal research are indeedclassiÞedĐincluding the budget of theprogram he oversees at Los Alamos (alaboratory spokesperson would say onlythat the Þgure is Ịin the millionsĨ) But

he contends that although he is in favor

of relaxing restrictions, the decision isnot his to make He also denies coopt-ing ideas from the Morrises He assertsthat he wrote a paper on nonlethalityÞve years ago and that the basic con-cept had been discussed by defense an-alysts since at least 1972 ỊClaiming tohave invented this concept is analo-gous to claiming to have developed civ-

il rights,Ĩ he declares ĐJohn Horgan

KUWAIT PRIZE 1994 Invitation to Nominations

The Kuwait Prize was institutionalized to recognize distinguished

accomplishments in the arts, humanities and sciences.

The Prizes are awarded annually in the following categories:

A Basic Sciences

B Applied Sciences

C Economics and Social Sciences

D Arts and Letters

E Arabic and Islamic Scientific Heritage

The Prizes for 1994 will be awarded in the following fields:

A Basic Sciences: Molecular Biology

B Applied Sciences: Nutrition and Related Diseases

C Economics and Social Sciences: Development of Arab Human Resources

D Arts and Letters: Comparative Literature

E Arabic and Islamic Scientific Heritage: Mining and Metallurgy

Foreground and Conditions of the Prize:

1 Two prizes are awarded in each category:

*A Prize to recognize the distinguished scientific research of a Kuwaiti,

and,

*A Prize to recognize the distinguished scientific research of an Arab

citizen

2 The candidate should not have been awarded a Prize for the submitted

work by any other institution

3 Nominations for these Prizes are accepted from individuals, academic

and scientific centres, learned societies, past recipients of the Prize,

and peers of the nominees No nominations are accepted from political

entities

4 The scientific research submitted must have been published during

the last ten years

5 Each Prize consists of a cash sum of K.D 30,000/-(U.S

$100,000/-approx.), a Gold medal, a KFAS Shield and a Certificate of Recognition

6 Nominators must clearly indicate the distinguished work that qualifies

their candidate for consideration

7 The results of KFAS decisions regarding selection of winners are final

8 The papers submitted for nominations will not be returned regardless

of the outcome of the decision

9 Each winner is expected to deliver a lecture concerning the contribution

for which he was awarded the Prize

Inquiries concerning the Kuwait Prize and nominations including complete

curriculum vitae and updated lists of publications by the candidate with

four copies of each of the published papers should be received before

31/10/1994 and addressed to:

The Director General The Kuwait Foundation for the Advancement of Sciences

P.O Box: 25263, Safat-13113, Kuwait Tel: +965 2429780 Fax : +965 2415365

Look for the Reader Service Directory

(page 105) for additional information

from the advertisers in this issue.

Trang 12

more lethal diseases do, even though

they aÝect a lot fewer people.Ó

Endometriosis is a disease of

rene-gade cells Tissue from the uterine

lin-ing proliferates in other areas of the

body, such as the bladder, intestine or,

in rare cases, the lung How these cells

reach the distant organs remains

un-known One theory holds that rather

than draining out of the body,

menstru-al blood ßows backward into the fmenstru-allo-

fallo-pian tubes and moves on from there

Regardless of where they end up,

endo-metrial cells continue to respond to the

hormonal pulses of the menstrual

cy-cle When estrogen levels increase, the

cells act as the uterine lining does, by

building up; when progesterone rises,

they slough oÝ, causing internal

bleed-ing This shedding can cause great pain

The discomfort caused by

endome-triosis has often been considered an

unfortunate but untreatable aspect of

womenÕs biology: excruciating

menstru-al periods are just some womenÕs lot

For that reason, physicians frequently

did not recognize the disease until it

was severe, often requiring the removal

of uterus and ovaries The

Endometrio-sis Association, a Milwaukee-based

or-ganization, reports that 70 percent of

women diagnosed with endometriosis

were initially told by their doctors that

there was no physical reason for theirpain Black women were told a slightlydiÝerent story : 40 percent of those suf-fering intense pelvic pain that proved

to be endometriosis were told they had

a sexually transmitted disease

Identifying endometriosis has come easier in the past decade because

it is more widely recognized and cause laparoscopyÑthe insertion of atiny viewing tube into the abdomenÑfacilitates seeing the growths But untilrecently, the enigma of its etiologyseemed impenetrable The disease wasassociated with many variables, includ-ing immune disorders such as lupus,with cancer, with the use of intrauter-ine devices ( IUDs) and, most consis-tently, with infertility

be-Between 30 and 40 percent of

wom-en who are treated for infertility haveendometriosis, although it is not clearwhich condition, if either, causes theother For many years, womenÕs careerswere deemed responsible Researchersannounced that delaying childbirth wasthe problem: the more periods a wom-

an has in her life, the more susceptibleshe is But Òit is very easy to demolishthat argument,Ó comments Mary LouBallweg, president and executive direc-tor of the Endometriosis Association

Ballweg says many women experience

their Þrst symptoms in their teens: 41percent of women diagnosed with en-dometriosis had symptoms before theage of 20 ÒI donÕt think we are going

to want to tell 13-year-olds to go outand get pregnant as a form of preven-tion,Ó she adds

Today Òendometriosis appears to bemore of an immunologic than a repro-ductive disorder,Ó Ballweg explains.ÒAnd when you look at the dioxin liter-ature, everything starts falling intoplace.Ó Dioxins are pollutants created

in certain industrial processes; themost potent of the 75 kinds is 2,3,7,8-

tetrachlorodibenzo-p-dioxin, or TCDD.

The link between TCDD and triosis was made last November, when

endome-Rier reported in Fundamental and

Ap-plied Toxicology that 79 percent of the

females in a rhesus monkey colony posed to dioxin developed endometri-osis The monkeys were exposed 15years ago and subsequently monitored.After three of the monkeys werefound to have widespread endometri-osis, the rest of the colony was exam-ined The prevalence and severity ofthe disease correlated with exposure:

ex-43 percent of the animals who receivedÞve parts per trillion (ppt) of dioxin de-veloped moderate to severe endometri-osis, as did 71 percent of those exposed

Trang 13

to 25 ppt (An average person has about

seven ppt of TCDD; the people most

contaminated in the 1976 industrial

ac-cident in Seveso, Italy, had 56,000 ppt

in their blood.)

Other Þndings support the dioxin

connection In 1992 German

research-ers announced that women with high

blood levels of polychlorinated

biphe-nyls ( PCBs), compounds related to

di-oxins, have a greater than normal

inci-dence of endometriosis Scientists at

the Department of Health and Welfare

in Canada have also found that many

female rhesus monkeys exposed to

PCBs developed endometriosis These

data have not yet been published

After RierÕs Þndings, Boyd and his

colleagues began evaluating blood

lev-els of dioxins and 200 related

com-pounds in women with endometriosis

Brenda Eskenazi of the University of

California at Berkeley and Paolo

Moca-relli of the University of Milan will

study dioxin-exposed women in

Seve-so ÒThere have been a lot of studies of

occupationally exposed males, and we

really need some on women,Ó notes

Linda Birnbaum, a toxicologist at the

Environmental Protection Agency, who

studies rodent models of the disease

The dioxin Þndings are intriguing

be-cause researchers are increasingly

con-vinced that the pollutant acts like a mone, often mimicking estrogen, anddisturbs the immune system Scientistshave observed immunologic dysfunc-tion in animals exposed to the contam-inant At least one researcher has re-ported similar disturbances in childrenborn to dioxin-exposed mothers, al-though these data have not yet beenpeer-reviewed The mechanisms of suchinteractions remain hidden for now,but it is evident that Òthese systems donot function alone,Ó Rier says ÒChang-

hor-es in the endocrine system cause

chang-es in the immune system.Ó

In addition to Þnding a correlationbetween dioxin and endometriosis, Rierfound immunologic changes in themonkeys that reßect those seen in peo-ple Women with endometriosis oftenhave very aggressive macrophages, atype of immune system cell, in the peri-toneum These macrophages secretecytokines and growth factors that canirritate endometrial cells Rier cautionsthat the monkey data are preliminaryand that no one knows if changes inthe immune system result from dioxin

or from endometriosis Nevertheless,the research creates excitement ÒThewhole issue of the immune system isfascinating; it is the right track,Ó con-curs David L Olive, a reproductive en-

docrinologist at the Yale UniversitySchool of Medicine

Another interesting aspect of the mune system work may clarify the re-lation between endometriosis and in-fertility Bruce A Lessey, a reproductiveendocrinologist at the University ofNorth Carolina at Chapel Hill, has iden-tiÞed a receptor, called beta-3, for acell-adhesion molecule absent in wom-

im-en with im-endometriosis These moleculeshave many functions, including a role

in immune response Lessey also foundbeta-3 to be missing in some infertilewomen Beyond potentially serving as ameans of identifying and treating en-dometriosis and infertility, informationabout beta-3 Òcould be used to make acontraceptive,Ó Lessey exclaims.Taken together, the dioxin and im-munologic research indicates that a ful-ler understanding of endometriosis maynot be far-oÝ In this context, the sug-gested rise in incidence could be omi-nous Environmental distribution of di-oxin and its cousins has been spread-ing Given Òthat dioxin is an endocrinedisrupter and that there is a tight link-age between the immune system andendometriosis, it is not inconceivablethat incidence is increasing and thatthe age of onset is decreasing,Ó Birn-baum notes ÑMarguerite Holloway

SCIENTIFIC AMERICAN April 1994 27

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Silly Season

A brace of nutty events: read

only if suÝering cabin fever

The observation that things are

not always what they seem may

be particularly true in the realm

of scientiÞc inquiry History, or at least

its Þrst draft in print, often needs to be

corrected Consider the case of Fannia

scalaris For 30 years, experts believed

this species of ßy had long gone

un-changed One specimen, preserved in

amber from the Baltic region some 38

million years ago, gave F scalaris its

reputation Entomologist Willi Hennig

Þrst examined the fossil in 1966

As-tonishingly, he reported that the

pre-historic houseßy was identical in every

way to common latrine ßies of the 19th

century Such an evolutionary feat was

widely celebrated and hardly

ques-tionedÑuntil last fall, that is

While poring over the collection of

12,500 fossil insects at the Natural

His-tory Museum in London, Andrew Ross,

a scholar of ancient bugs, noticed

some-thing peculiar about the prized piece of

amber ÒA crack appeared around the

ßy,Ó Ross says ÒI realized something

was very wrong.Ó Indeed, the specimen

showed the handiwork of an unknown,ßy-by-night forger

On further inspection, Ross ered that the genuine Baltic amber hadbeen split, carved, adorned with a pass-ing pest, Þlled with an amber resin andglued back together to form a nearlyßawless fake ÒThe entomologists arepleased because you shouldnÕt Þnd such

discov-an advdiscov-anced ßy living that long ago,ÓRoss says about reactions to his revela-tion ÒI donÕt think anyone had reallylooked at the specimen after Hennig,Ó

he adds A simple case of mistakenidentity

But some matters are less ent than ancient amber Reports widelycirculated in the popular press havesuggested that anyone can increase his

transpar-or her I.Q by listening to Mozart Thissupposed quick Þx is false The confu-sion began after Frances H Rauscher

of the University of California at Irvine

wrote a letter to Nature last fall In her

correspondence, Rauscher discussed acorrelation she had observed betweenenhancement of spatial reasoning abili-ties and the act of listening to music

She tested 36 volunteers in the lowing manner : Each participant lis-tened to 10 minutes of MozartÕs Sonatafor Two Pianos in D Major and then an-swered questions taken from the Stan-

fol-ford-Binet intelligence test that gaugespatial reasoning abilities The exercisewas repeated two more times, using dif-ferent listening conditionsÑa spokenvoice and silenceÑand diÝerent ques-tions RauscherÕs data showed that I.Q.scores based on spatial abilities alonewere on average eight to nine pointshigher for those tests the subjects tookafter listening to Mozart

Rauscher explains that her work isbased on the premise that listening tomusic and performing a spatial taskprime the same neural Þring patterns.But thatÕs just a guess ÒWeÕve heard alot of skepticism, including from our-selves,Ó she says ÒItÕs disturbing thatthere have been so many misinterpre-tations claiming things we never said.ÓNevertheless, some inaccuracies willstay on the books Take, for example,the big bang, a name given to the theo-

ry that suggests that our universe gan in a great explosion Astronomywriter Timothy Ferris argued in an es-

be-say in Sky & Telescope magazine last

August that the term was misleading

He noted that whatever happened backthen, before time and space, truly wasnot big and probably did not go bang.Moreover, about 40 years ago, FredHoyle, who tenaciously supports asteady state theory of the universe, in-

Trang 15

Super Progress

Defects pin intrusive magnetic Þelds in superconductors

Researchers trying to make

use-ful products from ture superconductors are hin-dered by the materialsÕ reluctance tocarry a current without resistance instrong magnetic Þelds These Þelds,produced externally or by the resis-tanceless ßow itself, appear in such en-visioned uses as motors and genera-tors Recently workers have achievedsigniÞcant breakthroughs in tamingthe disruptive eÝects

high-tempera-Magnetic Þelds hamper current ßow

by penetrating into a superconductor

as discrete bundles of ßux called tices When these vortices move about,they disperse energy and impede theßow Keeping the current moving with-out dissipation means anchoring theßux lines One approach creates traps,usually by bombarding samples withheavy ions If the ionsĐatoms stripped

vor-of their electronsĐare suÛciently sive, they leave columnar tracks thathold the ßux lines in place

mas-Unfortunately, these ions travel onlyabout 20 to 50 microns through the

substance They have diÛculty passingthrough the silver cladding that envel-ops commercially made superconduct-ing wire tapes ỊThe heavy ions are out

of juice by the time they reach the perconductor, so they cannot maketracks,Ĩ says Lia Krusin-Elbaum of theIBM Thomas J Watson Research Center

su-To sidestep that problem, baum and her collaborators from sixinstitutions accelerated much less mas-sive particles: protons High energy ismore easily imparted to protons, whichpenetrate farther into a sample than doions Although protons are too light tocreate pinning defects, the researcherspostulated that they might induce Þs-sion in the material The process wouldsend out as by-products heavy ionsthat would create pinning sites.The experiment bore out the predic-tions Using equipment at Los AlamosNational Laboratory, the workers accel-erated protons to 800 million electronvolts and directed them at a bismuth-based superconducting tape At suchenergies, the protons could whiskthrough more than half a meter of ma-terial Electron micrographs indicatedthat the protons caused some of thebismuth to Þssion into heavy ions ofxenon and krypton Speeding out of thematerial, the heavy elements left co-

Krusin-El-SCIENTIFIC AMERICAN April 1994 29

vented the term to mock the whole idea

Following FerrisÕs lead, Sky &

Tele-scope sponsored a contest challenging

anyone to come up with a more

accu-rate catchphrase to describe the event

At the January meeting of the

Ameri-can Astronomical Society, the editors

announced that there were no winners

Although they had received 13,099

en-tries, not one could match the wit and

fame of the big bang name

The three judgesĐFerris, Carl Sagan

of Cornell University and ABCÕs Hugh

DownsĐtossed out What Happens If I

Press This Button?, Jurassic Quark and

YouÕre Never Going to Get It All Back in

There Again They discarded acronyms

such as NICK ( NatureÕs Initial Cosmic

Kickstart) of Time, SAGAN (ScientiÞc

Ap-prehension of GodÕs Awesome Nature)

and Big TOE ( Theory of Everything).

Downs and Ferris each picked a few

favorites, but their semiÞnalists did

not match Sagan did not like any of

the proposals ỊThe idea of space-time

and matter expanding together and not

ƠintoÕ anything may be permanently

be-yond reach in the universe of short and

lucid phrases,Ĩ Sagan said last summer

So even if F scalaris is a fraud and

Mozart wonÕt make you smart, in the

end, it will still be the big bang in the

beginning ĐKristin Leutwyler

Trang 16

lumnar defects in the superconductor.

As a result, the superconductor couldcarry at 30 kelvins up to 1,000 timesmore current than before

Fission produces tracks called splayedcolumnar defects Such defects are aparticularly eÝective means of pinningßux They induce the magnetic vortices

to become intertwined with one

anoth-er ÒBecause everything is crossed andtangled up by the splay, the moststrongly pinned ßux lines will hold themore weakly held ones,Ó explains Da-vid R Nelson, one of the architects ofthe idea of splayed defects The experi-ment with proton irradiation suggeststhat substances riddled with splayedcolumnar defects are three times aseÝective in holding ßux lines than areparallel columns

Pinning with protons may not requirethe use of a big accelerator Conceiv-ably, much less energetic protonsÑandhence much smaller devicesÑmay beable to induce Þssion ÒThirty millionelectron volts should be more thanenough to make the proton penetratethe charge barrier of the nucleus,Ó Nel-son observes

Findings from Carlos A Duran, Peter

L Gammel and David J Bishop of AT&T

Bell Laboratories suggest that ßux ners may have another tool to explorebesides Þssion By using polarized lightand a special kind of magnetic coatinglaid on top of a superconductor, Bish-opÕs group has produced novel opticalimages of a magnetic Þeld intrudinginto a superconductor

pin-The images revealed a surprise

Rath-er than entRath-ering as a uniÞed front, aweak magnetic Þeld branches in, muchthe way a river running down a moun-tain produces rivulets Each branchpoint appears to mark an area resistant

to the intrusion ÒThe images show that

we donÕt understand in detail ßux etration,Ó Bishop says ÒThe patternswould suggest new strategies for pin-ning the ßux.Ó Making superconductingwires in layers, for instance, could help.Like ripstop fabric, the layers would ar-rest the branching and limit the pene-tration of the magnetic Þeld into thesuperconductor

pen-Of course, widespread applications

of the high-temperature materials willdepend as much on durability and han-dling as they do on resisting magneticÞelds But in terms of holding the lines,investigators seem closer than ever to

DENDRITES OF MAGNETIC FIELD 120 gauss strong penetrate from the side of a niobium superconducting thin Þlm The Þngers average about 60 microns long.

Trang 17

IÕve gone from politically very

incor-rect in the Õ70s to politically very

correct in the Õ90s,Ĩ muses Edward

O Wilson ỊAnd I have to add that I

wanted neither distinction, because I

donÕt even think in terms of whatÕs

cor-rect or incorcor-rect.Ĩ Wilson, or at least

his public persona, has undergone a

re-markable transformation over the past

two decades Today he is widely known

and admired for his

pas-sionate defense of the biota,

most recently in his 1992

best seller The Diversity of

Life In the late 1970s,

how-ever, Wilson was reviled by

some scientists and political

activists for his espousal of

sociobiology, whose premise

is that just as the social

be-havior of ants can be

under-stood by examining their

ge-netic underpinnings, so can

that of humans

When I Þrst meet Wilson

in his oÛce at Harvard

Uni-versityÕs Museum of

Com-parative Zoology, I have a

hard time imagining him at

the center of any

controver-sy The 64-year-old Baird

Professor of Science seems

too gracious, even eager to

please, and he keeps talking

about antsĐnot

surprising-ly, since he is the worldÕs

leading authority on them

This is a man who once

wrote that Ịants gave me

ev-erything, and to them I will

always return, like a shaman

reconsecrating the tribal

totem.Ĩ

When I ask if science has

anything more to learn about

the tiny creatures, Wilson

cries, ỊWeÕre only just beginning!Ĩ He is

now embarked on a survey of Pheidole,

a genus thought to include more than

2,000 species of ants, most of which

have never been described or even

named ỊI guess with that same urge

that makes men in their middle age

de-cide that at last they are going to row

across the Atlantic in a rowboat or join

a group to climb K2, I decided that I

would take on Pheidole.Ĩ

WilsonÕs Ịgrand goalĨ is to make

Pheidole a benchmark of sorts for

biol-ogists seeking to monitor biodiversity

Drawing on HarvardÕs vast collection ofants, he has been generating descrip-tions and painstaking pencil drawings

of each species of Pheidole ỊIt probably

looks crushingly dull to you,Ĩ Wilsonapologizes as we ßip through his draw-ings He confesses that when he peersthrough his microscope at a previously

unknown species, he has Ịthe sensation

of maybe looking uponĐI donÕt want

to get too poeticĐof looking upon theface of creation.Ĩ

I Þrst detect a martial spirit glintingthrough this boyish charm when heshows me the leafcutter ant farmsprawling across a counter in his oÛce

The scrawny little specimens scurryingacross the surface of the spongelikenest are the workers; the soldiers lurkwithin Wilson pulls a plug from the

top of the nest and blows into the hole

An instant later several bulked-up hemoths boil to the surface, BB-sizeheads tossing, mandibles agape ỊTheycan cut through shoe leather,Ĩ he says,

be-a bit too be-admiringly ỊIf you tried to diginto a leafcutter nest, they would grad-ually dispatch you, like a Chinese tor-ture, by a thousand cuts.Ĩ He chuckles Later, Wilson emphasizes that al-though he has not written much aboutsociobiology per se lately, its preceptsinform all his work, on biodiversity as

well as on ants Moreover, hestill harbors vast ambitionsfor human sociobiology Hethinks it has the potential toỊsubsume most of the socialsciences and a great deal ofphilosophyĨ and bring aboutprofound changes in politicsand religion He scoldsAmericans for their contin-ued reluctance to confrontthe role played by genes inshaping human behavior.ỊThis country is so seized

by our civic religion, tarianism, that it just avertsits gaze from anything thatwould seem to detract fromthat central ethic we havethat everybody is equal, thatperfect societies can be builtwith the goodwill of people.Ĩ

egali-As he delivers this sermon,WilsonÕs long-boned face,usually so genial, is as stony

as a Puritan preacherÕs.Ever the biologist, Wilsonhas described his own career

as a series of adaptations toenvironmental stresses Hisfather was a federal workerwho kept moving from town

to town in the Deep South.ỊBecause of the difficulty insocial adjustment that re-sulted from being a perpetu-

al newcomer,Ĩ Wilson has said, ỊI took

to the woods and Þelds.Ĩ At seven helost most of the vision in his right eyeafter accidentally stabbing it with the

Þn of a Þsh he had yanked from apond With acute though myopic vision

in his left eye, Wilson focused on mals he could scrutinize from shortrange, namely, ants

ani-Wilson pursued his studies at theuniversities of Alabama and Tennesseeand, from 1951 on, at Harvard He be-

PROFILE : EDWARD O WILSON

LORD OF THE ANTS: they Ịgave me everything,Ĩ says Wilson, shown here with a giant carpenter ant of Borneo.

Revisiting Old BattleÞelds

Trang 18

gan doing Þeldwork in such exotic cales as New Guinea, Fiji and Sri Lanka,discovering ant species that exhibited

lo-a flo-antlo-astic lo-arrlo-ay of socilo-al structures

Working in the laboratory, Wilson alsohelped to show that ants and other so-cial insects exchange information bymeans of a host of chemical messen-gers, named pheromones

WilsonÕs foray into sociobiology wasspurred at least in part by a threat tohis scientiÞc tribe In the late 1950s mo-lecular biologists, exhilarated by theirability to decipher the genetic code, be-gan questioning the value of taxonomyand other whole-animal approaches tobiology Wilson has alleged that James

D Watson, the co-discoverer of DNA,who was then at Harvard, Òopenly ex-pressed contempt for evolutionary bi-ology, which he saw as a dying vestigethat had hung on too long at Harvard.ÓThe memory still rankles, especiallysince taxonomyÕs status relative to mo-lecular biology may have fallen evenfurther Wilson deplores that situation

ÒI think a world biological survey would

do more for humanity during the next

20 years than the genome mappingproject,Ó he declares

Wilson responded to the challengefrom molecular biologists by broaden-ing his outlook, seeking the rules of be-havior governing not only ants but allsocial animals That eÝort culminated

in Sociobiology Published in 1975, it

was a magisterial survey of social mals, from termites to baboons Draw-ing on the vast knowledge he had accu-mulated in disciplines such as ethologyand population genetics, Wilson showedhow mating behavior, division of laborand other social phenomena were adap-tive responses to evolutionary pressure

ani-Only in the last chapter did Wilsonshift his sights to humans He arguedthat warfare, xenophobia, the domi-nance of males and even our occasion-

al spurts of altruism all spring at least

in part from our primordial compulsion

to propagate our genes Wilson has mitted that his style was Òdeliberatelyprovocative,Ó but he insists that he wasnot seeking or expecting trouble ÒIstumbled into a mineÞeld.Ó

ad-The book was for the most part vorably reviewed Yet a group of scien-tistsÑnotably Stephen J Gould andRichard C Lewontin, also biologists atHarvardÑattacked Wilson for promot-ing an updated version of social Dar-winism and providing a scientiÞc justi-Þcation for racism, sexism and nation-alistic aggression The criticism peaked

fa-at a scientiÞc conference in 1978, when

a radical activist dumped a pitcher ofwater on WilsonÕs head while shouting,ÒYouÕre all wet!Ó

While granting that support for hisproposals Òwas very slimÓ in the 1970s,Wilson asserts that Òa lot more evidenceexists todayÓ that human traits canhave a genetic basis To be sure, manyscientists, particularly in the U.S., shunthe term ÒsociobiologyÓ because it isstill Òfreighted with political baggage.ÓNevertheless, disciplines with such Òcir-cumlocutoryÓ names as Òbioculturalstudies,Ó ÒDarwinian psychologyÓ andÒevolutionary biological studies of hu-man behaviorÓ are all actually ÒsprigsÓgrowing from the trunk of sociobiolo-

gy, according to Wilson

Ironically, Wilson himself, at the very

end of Sociobiology, revealed some

trep-idation about the fruit that the Þeldmight bear ÒWhen we have progressedenough to explain ourselves in thesemechanistic terms,Ó he wrote, Òand thesocial sciences come to full ßower, theresult might be hard to accept.Ó Wilsonacknowledges that he Þnished the bookÒin a slight depressionÓ caused by hisfear that a complete sociobiological the-ory would destroy our illusions and end,

in a sense, our capacity for intellectualand spiritual growth

He worked his way out of that passe by determining that at least twoenterprises represented Òunending fron-tiers.Ó One was the human mind, whichhas been and is still being shaped bythe complex interaction between cultureand genes ÒI saw that here was an im-mense unmapped area of science andhuman history that we would take for-ever to explore,Ó he says ÒThat made

im-me feel much more cheerful.Ó He wrotetwo books on the topic with Charles J.Lumsden of the University of Toronto:

Genes, Mind and Culture in 1981 and Promethean Fire in 1983.

The other endeavor that Wilson ized could engage humanity forever wasthe study of biodiversity ÒWith millions

real-of species, each one with an almost imaginably complex history and genet-

un-ic makeup, we would have a source ofintellectual and aesthetic enjoyment forgenerations to come.Ó Wilson thinks thisquest may be propelled by Òbiophilia,Ó

a genetically based concern that mans have for other organisms

hu-He explored this theory in his 1984

book Biophilia While compiling

statis-tics on the abundance of species for thebook, however, he fell into another de-pression Species, he found, were van-ishing at an alarming rate; the diversity

he so cherished was in mortal danger.That realization catapulted him intohis role as a champion of biodiversity.WilsonÕs writings on biodiversityhave been praised even by some of his

former critics Gould, in a review in

Na-ture, lauded The Diversity of Life as Òa

Trang 19

thoroughly successful mixture of

infor-mation and prophecy.Ó Yet this embrace

was not complete; Gould derided the

biophilia theory, arguing that humans

show as great a propensity for

destruc-tion of life as for preservadestruc-tion of it

ÒThat has been due more to

igno-rance in humanityÕs history than desire

to wipe other forms of life oÝ the earth,Ó

Wilson retorts Gould, with whom

Wil-son is Òquite friendly,Ó is Òallergic to

any idea that human nature has a

bio-logical basis, and I must say I believe he

is nearly alone in that perception now.Ó

Wilson intends to take up the banner

of sociobiology again in two upcoming

books ( A self-confessed Òworkaholic,Ó

Wilson has already written or edited 18

books and more than 300 scientific

and popular articles.) One is a full-scale

autobiography he has nearly

complet-ed and hopes will be publishcomplet-ed by the

end of this year ÒI am revisiting all the

old battlefields,Ó he remarks

WilsonÕs next book will address

Ònat-ural philosophy,Ó a hoary term he has

revived to refer to Òthe still uncharted

and relatively vaguely defined region

between biology, the social sciences,

moral reasoning and the environment.Ó

Perhaps the bookÕs most radical theme

will be that findings from evolutionary

biology can guide us in resolving moral

disputes over topics as diverse as the

preservation of species or birth control

Most philosophers and even scientists

believe evolutionary biology Òcannot be

prescriptive,Ó Wilson states ÒThat is

true to a certain extent,Ó he adds, Òbut

my position is that where we can agree

on moral precepts is governed very

much by our evolutionary history.Ó

Far from promoting fatalism,

knowl-edge of our evolutionary roots should

help liberate us from dangerous

pat-terns of behavior, according to Wilson

A society based on sociobiological

pre-cepts would allow us to develop a

more rational political system, one that

encourages the Òmaximum personal

growthÓ of humans while preserving

the environment

He points out, for example, that

evo-lutionary biology has shown that

sexu-al intercourse promotes parentsexu-al

bond-ing and so the stability of the entire

family These findings might persuade

the Catholic Church, which believes

that the primary purpose of sex is

pro-creation, to drop its prohibition against

birth control, thereby aiding eÝorts to

curb population growth Wilson seeks

to Òbuild bridgesÓ rather than to initiate

yet another controversy with such

ar-guments ÒI donÕt know exactly where

IÕm going to end up,Ó he says, Òbut I

hope itÕs not in the midst of another

Trang 20

The real wage of the average

Amer-ican worker more than doubled

between the end of World War II

and 1973 Since then, however, those

wages have risen only 6 percent

Fur-thermore, only highly educated

work-ers have seen their compensation rise;

the real earnings of blue-collar workers

have fallen in most years since 1973

Why have wages stagnated? A

con-sensus among business and political

leaders attributes the problem in large

part to the failure of the U.S to compete

eÝectively in an increasingly integrated

world economy This conventional

wis-dom holds that foreign competition has

eroded the U.S manufacturing base,

washing out the high-paying jobs that a

strong manufacturing sector provides

More broadly, the argument goes, the

nationÕs real income has lagged as a

re-sult of the inability of many U.S Þrms

to sell in world markets And because

imports increasingly come from Third

PAUL R KRUGMAN and ROBERT Z

LAWRENCE teach economics at the

Mas-sachusetts Institute of Technology and

at Harvard University, respectively

Krug-man works primarily on international

trade and Þnance; he is a leading

pronent of the view that historical and

po-litical factors play at least as strong a

role in trade as do underlying national

economic characteristics In 1991 he was

awarded the John Bates Clark Medal by

the American Economics Association

LawrenceÕs investigations focus on

inter-national trade, with particular attention

to its eÝects on the labor market He is

also a nonresident senior fellow at the

Brookings Institution

Trade, Jobs and Wages

Blaming foreign competition for U.S

economic ills is ine›ective

The real problems lie at home

by Paul R Krugman and Robert Z Lawrence

Trang 21

World countries with their huge

re-serves of unskilled labor, the heaviest

burden of this foreign competition has

ostensibly fallen on less educated

Amer-ican workers

Many people Þnd such a story

ex-tremely persuasive It links AmericaÕs

undeniable economic diÛculties to the

obvious fact of global competition In

eÝect, the U.S is ( in the words of

Presi-dent Bill Clinton) Ịlike a big corporation

in the world economyĨĐand, like many

big corporations, it has stumbled in the

face of new competitive challenges

Persuasive though it may be,

howev-er, that story is untrue A growing body

of evidence contradicts the popular

view that international competition is

central to U.S economic problems In

fact, international factors have played a

surprisingly small role in the countryÕs

economic diÛculties The

manufactur-ing sector has become a smaller part of

the economy, but international trade isnot the main cause of that shrinkage

The growth of real income has slowedalmost entirely for domestic reasons

AndĐcontrary to what even mosteconomists have believedĐrecent anal-yses indicate that growing internation-

al trade does not bear signiÞcant sponsibility even for the declining realwages of less educated U.S workers

re-The fraction of U.S workers

em-ployed in manufacturing has beendeclining steadily since 1950 Sohas the share of U.S output accountedfor by value added in manufacturing

(Measurements of Ịvalue addedĨ deductfrom total sales the cost of raw materi-als and other inputs that a companybuys from other Þrms.) In 1950 valueadded in the manufacturing sector ac-counted for 29.6 percent of gross do-mestic product ( GDP ) and 34.2 percent

of employment; in 1970 the shares were25.0 and 27.3 percent, respectively; by

1990 manufacturing had fallen to 18.4percent of GDP and 17.4 percent ofemployment

Before 1970 those who worried aboutthis trend generally blamed it on auto-mationĐthat is, on rapid growth of pro-ductivity in manufacturing Since then,

it has become more common to blamedeindustrialization on rising imports;indeed, from 1970 to 1990, importsrose from 11.4 to 38.2 percent of themanufacturing contribution to GDP.Yet the fact that imports grew whileindustry shrank does not in itself dem-onstrate that international competitionwas responsible During the same 20years, manufacturing exports also rosedramatically, from 12.6 to 31.0 percent

of value added Many manufacturingÞrms may have laid oÝ workers in theface of competition from abroad, butothers have added workers to producefor expanding export markets

To assess the overall impact of ing international trade on the size ofthe manufacturing sector, we need toestimate the net eÝect of this simulta-neous growth of exports and imports

grow-A dollar of exports adds a dollar to thesales of domestic manufacturers; a dol-lar of imports, to a Þrst approximation,displaces a dollar of domestic sales.The net impact of trade on domesticmanufacturing sales can therefore bemeasured simply by the manufacturingtrade balanceĐthe diÝerence betweenthe total amount of manufacturedgoods that the U.S exports and theamount that it imports ( In practice, adollar of imports may displace slightlyless than a dollar of domestic sales be-cause the extra spending may come atthe expense of services or other non-manufacturing sales The trade balancesets an upper bound on the net eÝect

of trade on manufacturing.)Undoubtedly, the emergence of per-sistent trade deÞcits in manufacturedgoods has contributed to the decliningshare of manufacturing in the U.S econ-omy The question is how large thatcontribution has been In 1970 manu-factured exports exceeded imports by0.2 percent of GDP Since then, therehave been persistent deÞcits, reaching

a maximum of 3.1 percent of GDP in

ATTACKS on imported products, such

as this Honda-bashing in Latrobe, Pa.,are often motivated by the perceptionthat foreign competition threatens jobs

in the U.S The authors argue that suchhostility is misguided because interna-tional trade exerts only minor effects

on the U.S labor market

Trang 22

1986 By 1990, however, the

manufac-turing deÞcit had fallen again, to only

1.3 percent of GDP The decline in the

U.S manufacturing trade position over

those two decades was only 1.5 percent

of GDP, less than a quarter of the 6.6

percentage point decline in the share

of manufacturing in GDP

Moreover, the raw value of the trade

deÞcit overstates its actual eÝect on the

manufacturing sector Trade Þgures

measure sales, but the contribution of

manufacturing to GDP is deÞned by

value added in the sectorÑthat is, by

sales minus purchases from other

sec-tors When imports displace a dollar of

domestic manufacturing sales, a

sub-stantial fraction of that dollar would

have been spent on inputs from the

service sector, which are not part of

manufacturingÕs contribution to GDP

To estimate the true impact of the

trade balance on manufacturing, one

must correct for this ÒleakageÓ to the

service sector Our analysis of data from

the U.S Department of Commerce puts

the Þgure at 40 percent In other words,

each dollar of trade deÞcit reduces the

manufacturing sectorÕs contribution to

GDP by only 60 cents This adjustment

strengthens our conclusion: if trade in

manufactured goods had been balanced

from 1970 to 1990, the downward trend

in the size of the manufacturing sector

would not have been as steep as it

ac-tually was, but most of the

deindustri-alization would still have taken place

Between 1970 and 1990 manufacturingdeclined from 25.0 to 18.4 percent ofGDP; with balanced trade, the declinewould have been from 24.9 to 19.2,about 86 percent as large

International trade explains only asmall part of the decline in the relativeimportance of manufacturing to theeconomy Why, then, has the share ofmanufacturing declined? The immedi-ate reason is that the composition ofdomestic spending has shifted awayfrom manufactured goods In 1970 U.S

residents spent 46 percent of their lays on goods (manufactured, grown ormined ) and 54 percent on services andconstruction By 1991 the shares were40.7 and 59.3 percent, respectively, aspeople began buying comparativelymore health care, travel, entertainment,legal services, fast food and so on It ishardly surprising, given this shift, thatmanufacturing has become a less im-portant part of the economy

out-In particular, U.S residents are ing a smaller fraction of their incomes

spend-on goods than they did 20 years ago for

a simple reason: goods have becomerelatively cheaper Between 1970 and

1990 the price of goods relative to vices fell 22.9 percent The physical ra-tio of goods to services purchased re-mained almost constant during thatperiod Goods have become cheaperprimarily because productivity in man-ufacturing has grown much faster than

ser-in services This growth has beenpassed on in lower consumer prices.Ironically, the conventional wisdomhere has things almost exactly back-ward Policymakers often ascribe thedeclining share of industrial employ-ment to a lack of manufacturing com-petitiveness brought on by inadequateproductivity growth In fact, the shrink-age is largely the result of high produc-tivity growth, at least as compared withthe service sector The concern, widely

INCREASING AUTOMATION has

permit-ted U.S factories to reduce employment

while maintaining output, as visible in

these photographs of mid-century and

modern automobile plants Evidence

suggests that earlier fears that machines

would replace people may be closer to

the mark than current worries about

foreign competition

MANUFACTURING SHARE of gross domestic product has

de-clined during the postwar era The sectorÕs share of domestic

employment has decreased even more rapidly (left ) Even if

the U.S were not importing more manufactured goods than itexports, however, correcting for trade balance shows that

most of the decline would still have taken place (right )

EMPLOYMENT

1970 1975 1980 1985 1990 YEAR

30

510

25

1520

0

HYPOTHETICAL

ACTUAL

Trang 23

voiced during the 1950s and 1960s, that

industrial workers would lose their jobs

because of automation is closer to the

truth than the current preoccupation

with a presumed loss of manufacturing

jobs because of foreign competition

Because competition from abroad

has played a minor role in the

contraction of U.S

manufactur-ing, loss of jobs in this sector because

of foreign competition can bear only a

tiny fraction of the blame for the

stag-nating earnings of U.S workers Our

data illuminate just how small that

fraction is In 1990, for example, the

trade deÞcit in manufacturing was $73

billion This deÞcit reduced

manufac-turing value added by approximately

$42 billion (the other $31 billion

repre-sents leakageÑgoods and services that

manufacturers would have purchased

from other sectors) Given an average

of about $60,000 value added per

man-ufacturing employee, this Þgure

corre-sponded to approximately 700,000 jobs

that would have been held by U.S

work-ers In that year, the average

manufac-turing worker earned about $5,000

more than the average

nonmanufactur-ing worker Assumnonmanufactur-ing that any loss of

manufacturing jobs was made up by a

gain of nonmanufacturing jobsÑan

as-sumption borne out by the absence of

any long-term upward trend in the U.S

unemployment rateÑthe loss of Ògood

jobsÓ in manufacturing as a result of

in-ternational competition corresponded

to a loss of $3.5 billion in wages U.S

national income in 1990 was $5.5

tril-lion; consequently, the wage loss from

deindustrialization in the face of

for-eign competition was less than 0.07

percent of national income

Many observers have expressed cern not just about wages lost because

con-of a shrinking manufacturing sector butalso about a broader erosion of U.S realincome caused by inability to competeeÝectively in world markets But theyoften fail to make the distinction be-tween the adverse consequences of hav-ing slow productivity growthÑwhichwould be bad even for an economy thatdid not have any international tradeÑand additional adverse eÝects thatmight result from productivity growththat lags behind that of other countries

To see why that distinction is tant, consider a world in which produc-tivity (output per worker-hour ) increas-

impor-es by the same amount in every nationaround the worldÑsay, 3 percent a year

Under these conditions, all other thingsremaining equal, workersÕ real earnings

in all countries would tend to rise by 3percent annually as well Similarly, ifproductivity grew at 1 percent a year, sowould earnings ( The relation betweenproductivity growth and earningsgrowth holds regardless of the absolutelevel of productivity in each nation;

only the rate of increase is signiÞcant.)Concerns about international com-petitiveness, as opposed to low produc-tivity growth, correspond to a situation

in which productivity growth in the U.S

falls to 1 percent annually while where it continues to grow at 3 percent

else-If real earnings in the U.S then grow at

1 percent a year, the U.S does not haveanything we could reasonably call acompetitive problem, even though itwould lag other nations The rate ofearnings growth is exactly the same as

it would be if other countries were ing as badly as we are

The fact that other countries are

do-ing better may hurt U.S pride, but itdoes not by itself aÝect domestic stan-dards It makes sense to talk of a com-petitive problem only to the extent thatearnings growth falls by more than thedecline in productivity growth.Foreign competition can reduce do-mestic income by a well-understoodmechanism called the terms of tradeeÝect In export markets, foreign com-petition can force a decline in the prices

of U.S products relative to those of

oth-er nations That decline typically occursthrough a devaluation of the dollar,thereby boosting the price of imports.The net result is a reduction in realearnings because the U.S must sell itsgoods more cheaply and pay more forwhat it buys

During the past 20 years, the U.S hasindeed experienced a deterioration inits terms of trade The ratio of U.S ex-port prices to import prices fell morethan 20 percent between 1970 and1990; in other words, the U.S had to ex-port 20 percent more to pay for a givenquantity of imports in 1990 than it did

in 1970 Because the U.S importedgoods whose value was 11.3 percent ofits GDP in 1990, these worsened terms

of trade reduced national income byabout 2 percent

Real earnings grew by about 6 cent during the 1970s and 1980s Ourcalculation suggests that avoiding thedecline in the terms of trade would haveincreased that growth to only about 8percent Although the eÝect of foreigncompetition is measurable, it can by nomeans account for the stagnation ofU.S earnings

per-A more direct way of calculating theimpact of the terms of trade on real in-come is to use a measure known as

Trang 24

command GNP ( gross national

prod-uct) Real GNP, the conventional

stan-dard of economic performance,

mea-sures what the output of the economy

would be if all prices remained

con-stant Command GNP is a similar

mea-sure in which the value of exports is

deßated by the import price index It

measures the quantity of goods and

services that the U.S economy can

af-ford to buy in the world market, as

op-posed to the volume of goods and

ser-vices it produces If the prices of

im-ports rise faster than export prices (as

will happen, for example, if the dollar

falls precipitously), growth in command

GNP will fall behind that of real GNP

Between 1959 and 1973, when U.S

wages were rising steadily, command

GNP per worker-hour did grow slightly

faster than real GNP per hourÑ1.87

percent per year versus 1.85 Between

1973 and 1990, as real wages

stagnat-ed, command GNP grew more slowlythan output, 0.65 percent versus 0.73

Both these diÝerences, however, aresmall The great bulk of the slowdown

in command GNP was caused by theslower growth of real GNP per work-erÑby the purely domestic impact ofthe decline in productivity growth

If foreign competition is neither the

main villain in the decline of ufacturing nor the root cause ofstagnating wages, has it not at leastworsened the lot of unskilled labor?

man-Economists have generally been quitesympathetic to the argument that in-creased integration of global marketshas pushed down the real wages of lesseducated U.S workers

Their opinion stems from a familiarconcept in the theory of internationaltrade: factor price equalization When arich country, where skilled labor isabundant (and where the premium forskill is therefore small ), trades with apoor country, where skilled workers arescarce and unskilled workers abundant,the wage rates tend to converge Thepay of skilled workers rises in the richcountry and falls in the poor one; that

of unskilled workers falls in the richcountry and rises in the poor nation

Given the rapid growth of exportsfrom nations such as China and Indo-nesia, it seems reasonable to supposethat factor price equalization has been

a major reason for the growing gap inearnings between skilled and unskilledworkers in the U.S Surprisingly, howev-

er, this does not seem to be the case

We have found that increased wage equality, like the decline of manufac-turing and the slowdown in real in-come growth, is overwhelmingly theconsequence of domestic causes.That conclusion is based on an ex-amination of the evidence in terms ofthe underlying logic of factor priceequalization, Þrst explained in a classic

in-1941 paper by Wolfgang F Stolper andPaul A Samuelson The principle ofcomparative advantage suggests that arich country trading with a poor one willexport skill-intensive goods (because ithas a comparative abundance of skilledworkers) and import labor-intensiveproducts As a result of this trade, pro-duction in the rich country will shift to-ward skill-intensive sectors and awayfrom labor-intensive ones That shift,however, raises the demand for skilledworkers and reduces that for unskilledworkers If wages are free to rise andfall with changes in the demand fordifferent kinds of labor (as they do forthe most part in the U.S.), the real wages

of skilled workers will rise, and those

of unskilled workers will decline In apoor country, the opposite will occur.All other things being equal, the ris-ing wage diÝerential will lead Þrms inthe rich country to cut back on the pro-portion of skilled workers that they em-ploy and to increase that of unskilledones That decision, in turn, mitigatesthe increased demand for skilled work-ers When the dust settles, the wage dif-ferential has risen just enough to oÝsetthe eÝects of the change in the indus-try mix on overall demand for labor.Total employment of both types of la-bor remains unchanged

According to Stolper and SamuelsonÕsanalysis, a rising relative wage forskilled workers leads all industries toemploy a lower ratio of skilled to un-skilled workers Indeed, this reduction

is the only way the economy can shiftproduction toward skill-intensive sec-tors while keeping the overall mix ofworkers constant

This analysis carries two clear ical implications First, if growing inter-national trade is the main force drivingincreased wage inequality, the ratio ofskilled to unskilled employment shoulddecline in most U.S industries Second,employment should increase more rap-idly in skill-intensive industries than inthose that employ more unskilled labor

empir-SHARE OF U.S DOMESTIC SPENDINGgoing to manufactured goods has de-clined substantially since 1960, althoughthe volume of goods purchased has not

(left ) Instead goods have simply

be-come cheaper relative to services ductivity growth in the manufacturingsector has far outpaced such growth inservice industries, especially during the

Pro-past 10 years (bottom ).

Trang 25

Recent U.S economic

his-tory confounds these

pre-dictions Between 1979 and

1989 the real compensation

of white-collar workers rose,

whereas that of blue-collar

workers fell Nevertheless,

nearly all industries employed

an increasing proportion of

white-collar workers

More-over, skill-intensive industries

showed at best a slight

ten-dency to grow faster than

those in which blue-collar

employment was high (

Al-though economists use many

diÝerent methods to

esti-mate the average skill level in

a given industrial sector, the

percentage of blue-collar

workers is highly correlated

with other measures and

easy to estimate.)

Thus, the evidence suggests

that factor price equalization

was not the driving force

be-hind the growing wage gap

The rise in demand for skilled

workers was overwhelmingly

caused by changes in demand

within each industrial sector,

not by a shift of the U.S.Õs

in-dustrial mix in response to

trade No one can say with

certainty what has reduced

the relative demand for less

skilled workers throughout

the economy Technological change,

es-pecially the increased use of

comput-ers, is a likely candidate; in any case,

globalization cannot have played the

dominant role

It may seem diÛcult to reconcile the

evidence that international competition

bears little responsibility for falling

wages among unskilled workers with

the dramatic rise in manufactured

ex-ports from Third World countries In

truth, however, there is little need to

do so Although the surging exports of

some developing countries have

attract-ed a great deal of attention, the U.S

continues to buy the bulk of its imports

from other advanced countries, whose

workers have similar skills and wages

In 1990 the average wages of

manufac-turing workers among U.S trading

part-ners (weighted by total bilateral trade)

were 88 percent of the U.S level

Im-ports (other than oil ) from low-wage

countriesÑthose where workers earn

less than half the U.S levelÑwere a

mere 2.8 percent of GDP

Finally, increasing low-wage

competi-tion from trade with developing nacompeti-tions

has been oÝset by the rise in wages

and skill levels among traditional U.S

trading partners Indeed, imports from

low-wage countries were almost aslarge in 1960 as in 1990Ñ2.2 percent

of GDPÑbecause three decades ago pan and most of Europe fell into thatcategory In 1960 imports from Japanexerted competitive pressure on labor-intensive industries such as textiles

Ja-Today Japan is a high-wage country,and the burden of its competition fallsmostly on skill-intensive sectors such

as the semiconductor industry

We have examined the case for

the havoc supposedly wrought

by foreign competition andfound it wanting Imports are not re-sponsible for the stagnation of U.S in-comes since 1973, nor for deindustrial-ization, nor for the plight of low-wageworkers That does not mean, however,

we believe all is well

Some of those who have raised thealarm about U.S competitiveness seem

to believe only two positions are ble: either the U.S has a competitiveproblem, or else the nationÕs economy

possi-is performing acceptably We agreethat the U.S economy is doing badly,but we Þnd that international competi-tion explains very little of that poorperformance

The sources of U.S ties are overwhelmingly do-mestic, and the nationÕsplight would be much thesame even if world marketshad not become more inte-grated The share of manu-facturing in GDP is decliningbecause people are buyingrelatively fewer goods; manu-facturing employment is fall-ing because companies arereplacing workers with ma-chines and making more eÛ-cient use of those they retain.Wages have stagnated be-cause the rate of productivitygrowth in the economy as awhole has slowed, and lessskilled workers in particularare suÝering because a high-technology economy has lessand less demand for their ser-vices Our trade with the rest

diÛcul-of the world plays at best asmall role in each case.The data underlying ourconclusions are neither sub-tle nor diÛcult to interpret.The evidence that interna-tional trade has had little netimpact on the size of themanufacturing sector, in par-ticular, is blatant The prev-alence of contrary viewsamong opinion leaders whobelieve themselves well in-formed says something disturbingabout the quality of economic discus-sion in this country

It is important to get these thingsright Improving American economicperformance is an arduous task It will

be an impossible one if we start fromthe misconceived notion that our prob-lem is essentially one of internationalcompetitiveness

INFORMATION AND SERVICE industries are taking on therole that manufacturing once held in the U.S economy

FURTHER READING

PROTECTION AND REAL WAGES W F

Stolper and P A Samuelson in Review

of Economic Studies, Vol 9, pages

58Ð73; November 1941

MYTHS AND REALITIES OF U.S

COMPETI-TIVENESS P R Krugman in Science, Vol.

254, pages 811Ð815; November 8, 1991.UNDERSTANDING RECENT CHANGES IN

THE WAGE STRUCTURE L Katz in NBER Reporter, pages 10Ð15; Winter 1992/93.

TRADE AND AMERICAN WAGES IN THE1980s: GIANT SUCKING SOUND OR SMALL

HICCUP? R Z Lawrence and M J

Slaugh-ter in Brookings Papers on Economic tivity: Microeconomics, Vol 2, 1993.

Ac-PEDDLING PROSPERITY: ECONOMIC SENSEAND NONSENSE IN THE AGE OF DIMIN-ISHED EXPECTATIONS P R Krugman

W W Norton Company, 1994

Trang 26

On a hot July afternoon the Mall

in Washington, D.C., is

over-run with sightseers They move

earnestly in zigzag patterns carrying

their coolers, bouncing from museum

to monument to cafeteria Most of the

streets bordering the lawns are ßat, and

as many tourists stroll in one direction

as in the other Suddenly a drumroll is

heard : a marching band is assembling

On the roads, displacing the confused

crowd, are gathering serried ranks of

uniformed high school students Soon

the band is mustered in neat rows,

hardly disturbed even by a child trying

to hide between the trumpetersÕ legs

from a pursuing parent As the

tour-ists watch, the band starts to play and

then marches forward with a clash of

cymbals

The wanderers on the Mall imitate

rather closely the behavior of electrons

in common metals On cooling to

tem-peratures close to absolute zero, most

metals remain in this state; that is, the

electrons continue to wander But in

some metals the electrons organize

themselves into regular patterns like

the ranks of a marching band

Such ordered ranks of electrons,

oth-erwise known as charge-density waves,

or CDWs for short, were envisaged by

the theoretical physicist Rudolf E

Peierls in the early 1930s and ered in the 1970s A related phenome-non, spin-density waves, or SDWs, werepredicted by Albert W Overhauser in

discov-1960, while at Ford Motor Company;

the waves were also Þrst seen in the1970s At one time, CDWs were suggest-

ed as being the agent of tivity Today we know that supercon-ductivity has a diÝerent origin, one inwhich the students dance in pairs rath-

superconduc-er than march; yet the many oddities ofthe marching bands themselves havekept researchers intrigued for decades

Charge-density waves may even Þndapplications one day as tunable capaci-tors in electronic circuits and as ex-tremely sensitive detectors of electro-magnetic radiation

Hook up a battery to the ends of asolid in which a CDW exists and apply

a voltage across it If the voltage issmall enough, nothing happens: theshoes of the marchers are stuck to theroad with chewing gum ( The sticking

is weak, so charge-density waves have

a Òdielectric constantÓ several milliontimes that of semiconductors, which al-lows them to store enormous amounts

of chargeÑhence their potential use ascapacitors.) But if you increase the volt-age beyond a certain threshold, theshoes suddenly break free, and theband begins to marchÑthere is a largecurrent The current is not proportion-

al to the voltage, as in ordinary metalsobeying OhmÕs law; instead it increasesvastly with small increases in voltage

Further, a small part of the total rent oscillates in time, even if only aconstant DC voltage is applied

cur-And charge-density waves exhibit aÒself-organizedÓ response to externallyapplied forces In fact, the concept ofself-organized criticality grew out of ini-tial work on CDWs This Þeld attempts

to understand the motions of complex

systems such as sandpiles or quake fault networks LetÕs say we drib-ble sand onto a surface It piles up into

earth-a conicearth-al shearth-ape; the cone is so steep thearth-atoften adding a single grain will cause anavalanche Likewise, tectonic plates per-petually poise themselves on the brink

of an earthquake In some

circumstanc-es, charge-density waves so conÞgurethemselves that any slight change in anexternally applied electric Þeld leads to

a drastic change CDWs are thus a top system in which we can test theo-ries of self-organization

table-Why do density waves form?

The underlying cause is the teraction between the elec-trons in a metal Normally the electro-static repulsion between the negativelycharged electrons is canceled out by thepresence of positive ions (atoms thathave lost one or more electrons and aretherefore positively charged ), whichform the body of the metal Then theelectrons hardly notice one another Insuch a situation, if we picture the elec-trons as the strolling crowd describedearlier, the probability of Þnding a per-sonÑor electronÑat any one spot is thesame as at any other So the electronsÕcharge density is uniform in space Nowsuppose the electrons do interactÑsay

in-by aÝecting the lattice in which the itive ions are arranged The lattice can

pos-in turn pos-inßuence the position of a ond electron, eÝectively giving rise to

sec-an interaction between the electrons

Charge and Spin Density Waves

Electrons in some metals arrange into crystalline patterns that move in concert, respond peculiarly

to applied voltages and show self-organization

by Stuart Brown and George GrŸner

STUART BROWN and GEORGE GR†NER

share an interest in the dynamics of

driven systems such as charge-density

waves and earthquakes GrŸner received

his Ph.D in Budapest in 1971 and worked

as a postdoctoral associate at Imperial

College, London He has been professor

of physics at the University of California,

Los Angeles, since 1981 Brown earned

his Ph.D in 1988 from U.C.L.A and did

postdoctoral research at Los Alamos

Na-tional Laboratory and the University of

Florida In 1991 he returned to U.C.L.A

as a member of the faculty

REGULAR PATTERN of charge-densitywaves in the material tantalum disul-Þde is revealed by a scanning tunnelingmicroscope Peaks of high charge den-

sity (white ) are spaced 12 angstroms

apart in a hexagonal array Robert V.Coleman and C Gray Slough of the Uni-versity of Virginia provided the scan

Trang 27

Trang 28

The interactions often cause the

elec-trons to become paired up; the pairs

subsequently repel one another Then

each pair stays as far away as possible

from all other pairs, and an ordered

structure like that of the marching band

is formed; the charge density becomes

bumpy If we take into account the wave

nature of the electrons, a smooth

varia-tion of the charge density emerges This

smooth spatial variation of the charge

is called a charge-density wave

In addition to charge, electrons

car-ry around with them something called

spin A spin is a magnetic moment

as-sociated with each electron; the

mo-ments can assume one of two states,

labeled ÒupÓ and Òdown.Ó If electrons

with the same spin orientation repel

one another, then each up spin wants

to have a down spin as a neighbor The

result is a spin-density wave, or SDW

An SDW can be thought of as two

CDWs, one for each spin state,

super-posed, with their peaks in alternate

po-sitions Note that for a charge-density

wave the charge varies in space, but

not for a spin-density wave

In general, how the electrons

inter-actÑand what kind of

quantum-me-chanical state is formedÑdepends onhow the electronsÕ motion is conÞned

In three dimensions, electrons have theability to avoid one another by simplymoving out of the way But if they arelimited to traveling along a chain ofatoms, the electrons cannot avoid oneanother and tend to interact morestrongly CDWs and SDWs occur mostly

in such materials, in which the atomsare lined up in chains ( Many of thesematerials were Þrst synthesized in theearly 1970s.) In some circumstances,the electron pairs attract rather thanrepel one another, forming a supercon-ducting state

Chemists often design materials with

a chainlike structure; however, they donot have much control over the nature

of the electronic interactions So

wheth-er the synthesized substance develops

a CDW or an SDW or becomes conducting cannot be predicted

super-Electrons tend to pair at low

tem-peratures At absolute zero, eachelectron has its Òmate,Ó and thestructure is fully ordered As we warm

up the material, some of the pairs come separated; they then induce oth-

be-er pairs to separate With highbe-er andhigher temperatures, more and morepairs are divorced, until the last pairbreaks up; above this critical tempera-ture the material has only free elec-trons and is back to a metal This pro-cess is known as a phase transition, as

in the melting of an ice cube If we verse the process, cooling the materialdown from high temperatures, a CDWforms when we cross the phase-transi-tion temperature The electrons thenget stuck Because small electric Þeldscan no longer dislodge them, and nocurrent ßows, the metal changes abrupt-

re-ly to an insulator This sudden change

in electric conductivity in fact signalsthe formation of a CDW

Far more direct observations of CDWshave been made using scanning tunnel-ing microscopes, which show the charge

density even on atomic scale [see

illus-tration on preceding page ] Further, a

CDW is accompanied by distortions inthe lattice The distortion pattern, called

a superlattice, can be seen by x-ray fraction: the ions scatter x-rays ontophotographic Þlm, displaying a charac-teristic pattern that reveals their spac-ing For example, if the superlatticewavelength is twice that of the latticewavelength, the x-ray diÝraction pat-tern will show additional spots halfwaybetween the main spots coming fromthe lattice (The intensity of the halfwayspots relates to the size of the latticedeformation.) The Þrst experiments ofthis type were performed by RobertComes and his associates in Paris inthe 1970s

dif-Since a spin-density wave leads ther to a charge ßuctuation nor to a lat-tice distortion, detecting it is muchharder In principle, it could possibly

nei-be seen through the magnetic force croscope, an instrument that responds

mi-to variations of the spin, but the

devic-es are not yet sensitive enough The Þrstdemonstration of spin-density waveswas made by scattering neutrons oÝchromium ( Neutrons, having spin and

no charge, are useful for studying dered spin structures.) In addition, in-direct probes of the magnetic Þeld,such as magnetic resonanceÑthe sametechnique used in hospitals as a diag-nostic toolÑare now the only means ofsensing the presence of SDWs

or-The eÝects of CDWs and SDWs mayalso be observed via the motions theyperform as a body These motions can

be rather diÝerent depending on howthe wavelength of the density wave re-lates to the underlying lattice spacing.The CDW wavelength changes with thenumber of electrons in the solid : ifthere are more electrons, the wave-length becomes smaller and, in particu-

Pairing States

Charge-density waves (top ) can be thought of as electron-hole pairs as

well as electron-electron pairs ( A hole is a vacant quantum-mechanical

state; it acts much like a particle.) Looking at the array, we can think of an

electron as being paired either with a hole to its right or left or with the

elec-tron opposite (Superconductivity comes from yet another kind of elecelec-tron-

electron-electron pairing.) In spin-density waves (bottom ), the opposing electron-electron is

shifted, so that the total charge density is constant but the spin density goes

up and down along the array

Which of the various pairing states occurs in a given material depends on

the strength of the various interactions between the electrons For instance,

if direct electrostatic repulsion between electrons dominates, either a

spin-density wave or a spin-parallel (or “triplet” ) superconducting state is favored

Electrons can also interact by distorting the lattice The mediation of the

lat-tice leads to attraction between electrons, and either a charge-density wave

or a spin-antiparallel (or “singlet” ) superconducting state results

ELECTRON

Trang 29

lar, may not match the original lattice

spacing of the ions in any neat way

Then the charge-density wave is said to

be ÒincommensurateÓ with the original

lattice spacing; it ßoats around

unaf-fected by the lattice until pinned down

by a defect ( A defect acts like a

pot-holeÑor chewing gumÑin the electric

potential surface, in which the CDW

gets stuck.) But if the charge-density

wave and the original lattice spacing

are ÒcommensurateÓ and Þt neatly,

then, for example, every other student

stands in a depression in the road, and

it is very hard to get the band moving

For this reason, incommensurate waves

are much more intriguing in the

varie-ties of behavior that they display

Com-mensurate wavesÑthe ones originally

envisioned by PeierlsÑare of largely

historical interest

There are two basic motions that

charge-density waves can indulge in as

a body, called collective modes

Quan-tum mechanics allows us to think of

these modes as particles, which are then

named by the suÛx Òon.Ó The ßoating

of the crests back and forth and their

occasional bunching are a kind of

col-lective mode known as a phason ( it

in-volves changing the ÒphaseÓ of the

den-sity wave) For waves that do not Þt

well with the underlying lattice

struc-ture, the ßoating takes no energy at all

(unless a defect pins the wave down),

but the bunching takes some The other

way in which CDWs can change is thatthe crests can get higher This motion,called an amplitudon, requires a lot ofenergy The position and height of thecrests may both vary, with variationsover shorter distances having higherenergies The energies of these motionswere Þrst calculated by Patrick A Lee,

T Morris Rice and Philip W Anderson,then at AT&T Bell Laboratories TheSDWs share these collective motionswith the CDWs and in addition have apurely magnetic mode that is related tochanges in spin orientation These exci-tations are called magnons

The truly dramatic motions occurwhen we apply an electric Þeld to a sol-

id containing a charge-density wave Acurrent-voltage relation very diÝerentfrom OhmÕs lawÑin which conductivi-

ty is constantÑwas found in 1986 ( inthe material niobium triselenide) byNai-Phuan Ong, Pierre Monceau andAlan M Portis of the University of Cali-fornia at Berkeley Since then, someCDW materials have displayed conduc-tivities that vary by several orders ofmagnitude when very modest electricÞelds (of less than one volt per centi-meter ) are applied We now know thatthis change in conductivity comes fromthe depinning and sudden motion ofthe entire density wave Even more un-usual is the variation of the current astime passes, even when only a constant(DC) voltage is applied This was Þrst

observed by Robert M Fleming andCharles C Grimes of AT&T Our recentmeasurements, and those of Denis JŽ-rome, Silvia Tomic and others at theUniversity of Paris South and TakashiSambongiÕs group at Hokkaido Uni-versity, have shown that spin-densitywaves behave much like charge-densitywaves in the presence of electric Þelds

The simplest model that describes

the behavior of density waves iscalled the classical particle mod-

el It was proposed by one of us ( ner ) with Alfred Zawadowski and Paul

GrŸ-M Chaikin, then at the University ofCalifornia at Los Angeles The charge-density wave is represented by a singlemassive particle positioned at its cen-ter of mass The behavior of this parti-cle reßects that of the entire array.When there are no external electricÞelds, the particle sits on a ribbed sur-face, like a marble in a cup of an eggtray This conÞguration corresponds tothe crest of a CDW being stuck at a de-fect If we move the CDW, the marbleclimbs over the edge of the eggcup andfalls into the next one, which meansthat the next crest of the CDW getsstuck at the same defect

This model allows us to understandmuch of the versatile behavior of CDWs.The marble is free to move around thebottom of the eggcup and can thereforereadjust its position sensitively in re-

CHARGE AND SPIN DENSITIES of electrons are shown in

nor-mal metals, charge-density waves and spin-density waves

The spin-up (orange ) and spin-down (purple ) electron

den-sities vary with position within the crystal They can be

summed to yield the total charge density (blue ); their ence yields the spin density (green ).

Trang 30

sponse to applied electric Þelds

Be-cause the marbleÑthat is, the

charge-density waveÑcarries charge, its

posi-tion affects the electric Þeld within the

medium The marble usually adjusts its

position so as to reduce the electric

Þeld acting on it Thus, materials with

charge-density waves have a large

Òdi-electric constant,Ó so large that they

could be called superdielectrics Our

measurements on both charge- and

spin-density waves give values for the

dielectric constant more than one

mil-lion times larger than that of ordinary

semiconductors

What happens if we apply a DC

volt-age? The egg tray on which the marble

lies will tilt If the tiltÑthat is, the

volt-ageÑis great enough, the marble can

roll out of the eggcup and down the egg

tray The marble slows down when itclimbs up an edge and speeds up when

it falls down one Consequently, itsspeed, and the electric current, goes upand down with time These current os-cillations, which we have mentionedearlier, are widely observed The aver-age current is higher if the tilt in the eggtrayÑthat is, the DC voltageÑis higher

Now suppose that instead of a DCvoltage, an AC voltage is applied, inwhich case the egg tray is rocked backand forth like a seesaw The marble os-cillates back and forth in its cup Thissloshing of the entire density wavescatters light of certain colors, allowingits detection in optical experiments atmicron and millimeter wavelengths, asconducted at U.C.L.A ( Conversely, theCDW can sensitively detect electromag-

netic radiation.) If we apply both a DCÞeld and an AC Þeld, the former makesthe egg tray tilt to one side, whereas thelatter makes it jiggle from side to side.Suppose the marble is rolling down theegg tray If the time the marble takes to

go from one eggcup to the next is

near-ly the same as the time for which theegg tray is tilted ÒupÓ by the AC voltage,

it will hop between eggcups once eachcycle of the AC Þeld When the marble

is hopping down the egg tray with thehelp of the AC Þeld, augmenting the av-erage tilt of the egg tray by increasingthe DC voltage does not change the av-erage current So if we plot the currentversus the DC voltage ( in the presence

of an AC voltage), we will see the rent generally increasing with DC volt-age except for certain plateaus where

so that the electric tivity might be from 10 to1,000 times greater in thechain direction than across

conduc-A typical linear-chain pound of the inorganic va-riety, K2Pt(CN)4Br0.33H2O,

com-or KCP fcom-or shcom-ort, is shown

at the left The verticallobes (purple ) show elec-

tron orbitals overlappingalong the chain Some oth-

er linear-chain compoundshaving so-called incom-mensurate charge-densitywaves are NbSe3, ( TaSe4)2Iand K0.3MoO3

The other types of CDWmaterials are grown fromflat organic molecules such

as the synthetic one, methyltetraselenafulva-lene, or TMTSF Several ofthese molecules are stacked on one another to form a crystal

tetra-together with embedded PF6ions, as shown at the right

Electrons are free to move up and down the stack but not

from one stack to the next; thus, the conductivity is again

highly anisotropic

These organic materials are of particular importance in

studying electrons in solids because their properties can be

fine-tuned For example, an entire family of TMTSF-based

salts can be created by replacing the PF6anion with ReO4, Br,

SCN or AsF6, among others Each new salt has slightly

differ-ent interaction strengths between the electrons; these

varia-tions can have profound effects The crystal ( TMTSF)2ClO4,

if cooled slowly down to one kelvin, becomes a

supercon-ductor, whereas rapid cooling gives a spin-density wave

CN

Pt

CH3

Trang 31

we have a Òmode lockingÓ [see bottom

illustration on this page].

The model we have described, and

the equations it implies for the marbleÕs

motion, turns out to be applicable in

quite diverse situations For example, it

describes a Josephson junction (that

between two superconductors), the

mo-tion of ions in solids, a pendulum in a

gravitational Þeld and certain

electron-ic circuits Although the equations look

simple, they display a variety of

solu-tions, including chaotic behavior

Other behaviors are not so simple to

understand By cooling materials that

contain spin-density waves down to

al-most absolute zero, we Þnd a peculiar

phenomenon that has been interpreted

as the marbleÕs tunneling through to the

next eggcup instead of climbing over

its edge This purely

quantum-mechan-ical eÝect has since been conÞrmed by

other groups Tunneling has been

pre-dicted by Kazumi Maki of the

Universi-ty of Southern California and by the late

John Bardeen of the University of

Illi-nois, but it is too early to tell whether

their model applies to our

low-tempera-ture experimental Þndings about SDWs

Perhaps the most bizarre behavior

of all is that of self-organization

[see ÒSelf-Organized Criticality,Ó

by Per Bak and Kan Chen; SCIENTIFIC

AMERICAN, January 1991] Susan N

Coppersmith and Peter B Littlewood of

AT&T and Kurt A Wiesenfeld and Per

Bak of Brookhaven National Laboratory

were the Þrst to deduce this

phenome-non, from experiments on CDWs

per-formed by researchers at AT&T and by

us at U.C.L.A Self-organization is a

phe-nomenon that charge-density waves

have in common with earthquakes Just

as two tectonic plates rubbing on each

other get stuck at ragged edges and

then suddenly unstick (with

catastroph-ic consequences), charge-density waves,

in the presence of some electric Þelds,

get stuck on defects and suddenly

un-stick But the analogy goes deeper

Earthquakes and charge-density waves

tend to settle into conÞgurations in

which a small disturbance will cause a

violent change: they organize

them-selves into a critical state The marble

balances itself exactly on the thin edge

between two eggcups

To study the self-organizing

behav-ior, we have to reÞne our model

slight-ly Self-organization comes from

self-interactions, so our model has to

in-clude the push-and-pull between the

diÝerent regions of the CDW One

mar-ble at the center of mass is no longer

enough; we now need a series of

mar-bles attached to their neighbors by

springs This arrangement represents

the elasticity of the density wave pose we repeatedly turn on a DC elec-tric Þeld for some time and then turn it

Sup-oÝ The marbles move some distanceduring the ÒonÓ time and roll to the bot-toms of eggcups when the Þeld isturned oÝ We would expect them tomove farther if the ÒonÓ time is longer

But what happens is actually quite ferent, as was found in simulations by

dif-Coppersmith Just before the Þeld isturned on, the marbles are positioned

in neighboring eggcups When the Þeld

is turned oÝ, each is found to be

exact-ly balanced on an edge between twoeggcupsÑno matter how long the Þeld

is kept on [see illustration on next

page] (After the Þeld is turned oÝ, the

marbles roll into eggcups, sometimes

to their right and sometimes to their

CHARGED-PARTICLE MODEL shows how current ßow in charge-density waves

diÝers from that in normal metals In a metal (left ) the particle rests on a ßat

(elec-trical potential ) surface If we apply a voltage, the surface tilts, and the particle

starts to move: there is a current For a charge-density wave (right ), the surface is

ribbed If the applied voltage is lowÑthat is, the tilt is smallÑthe particle changesposition only slightly, and there is no current If the tilt is large enough to get theparticle over the barrier, the particle runs down the ribbed surface Then the cur-rent goes up and down in time as the particle climbs over each barrier

CURRENT VERSUS VOLTAGE is plotted for metals and charge-density waves In a

metal (blue) the current increases linearly with voltage For a charge-density wave,

there is no current until the voltage increases to a critical value; only then does the

current start to ßow (red ) If in addition to a direct voltage we apply an alternating one, the curve shows plateaus (purple) The plateaus correspond to a Òmode lock-

ingÓ when the ßow of the charge-density wave matches the alternating frequency

HIGHVOLTAGE

LOWVOLTAGE

NOVOLTAGE

DIRECT VOLTAGE

0.01.02.03.0

CDW

CDW WITH ALTERNATINGVOLTAGEMETAL

Trang 32

left.) This bizarre self-regulatory havior is easier to study in charge-den-sity waves than in earthquakes It hasgiven the former a particular use intesting complex dynamical theories.

be-In fact, the density-wave states areprobably just the simplest periodic con-Þgurations of electrons we can hope toÞnd Several theories suggest a hierar-chy of more complex arrangements.One suggestion came from theoreticalphysicist Eugene Wigner in 1939 Wig-ner showed that if the density of elec-trons is low enoughÑsay in a collec-tion of electrons moving freely in twodimensionsÑthey would settle into acrystalline pattern Since then, manyresearchers have searched for ÒWignercrystals.Ó In the early 1980s Grimes andGregory Adams, also at AT&T, showedthat electrons deposited on the surface

of liquid helium form just such a tal Evidence of their presence in solid-state systems has come from groups atSaclay, France, AT&T and elsewhere.The various properties of density-wave materials have yet to be appliedtoward enhancing our comfort Still,plans abound The dielectric constants

crys-of CDW materials, besides being mous, also change with the electricÞeld; they could be implemented in cir-cuits as tunable capacitors The strongresponse of charge-density waves toelectromagnetic radiation could makethem useful as light detectors; at lowtemperatures, this sensitivity would ul-timately be limited by quantum me-chanics Bardeen, better known for thetheory of superconductivity and the in-vention of the solid-state transistor,worked out the theory of the quantumtransport of density waves Whetherquantum detectors such as he envis-aged can be built and put to practicaluse remains to be seen Right now, weare happy enough just to learn moreabout the idiosyncracies of charge- andspin-density waves

enor-FURTHER READINGTHE DIFFERENCE BETWEEN ONE-DIMEN-SIONAL AND THREE-DIMENSIONAL SEMI-CONDUCTORS Esther M Conwell in

Physics Today, Vol 38, No 6, pages 46Ð

CHARGE DENSITY WAVES IN SOLIDS

Edit-ed by L P GorÕkov and G GrŸner vier, 1990

Else-EVIDENCE ACCUMULATES, AT LAST, FORTHE WIGNER CRYSTAL Anil Khurana in

Physics Today, Vol 43, No 12, pages

17Ð20; December 1990

SELF-ORGANIZED BEHAVIOR is compared for models of charge-density waves and

earthquake faults The particles attached by springs represent the position and

elasticity of the charge-density wave (a) The particles rest on a ribbed surface If

one turns an electric Þeld on and oÝ repeatedly, the marbles are found to sit in the

most unstable position possible: each on top of a hill In the earthquake model (b)

the blocks are attached to a surface moving sideways with respect to the lower

surface The lower surface has metal strips that drag on the blocks; the blocks are

also connected by springs After some arbitrary (unpredictable) time, the

accumu-lated strain makes the blocks rearrange their positions catastrophically But the

new positions are again unstable The photograph shows the San Andreas fault in

Carrizo Plain, east of San Luis Obispo, Calif

CHARGE-DENSITY WAVE MODEL

EARTHQUAKE MODEL

a

b

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What causes the pity we might

feel for the melancholy Dane

in Hamlet or the chill during a

perusal of the Raven? Our brains have

absorbed from our senses a printed

se-quence of letters and then converted

them into vivid mental experiences and

potent emotions The Òblack boxÓ

de-scription of the brain, however, fails to

pinpoint the speciÞc neural processes

responsible for such mental actions

While philosophers have for centuries

pondered this relation between mind

and brain, investigators have only

re-cently been able to explore the

connec-tion analyticallyÑto peer inside the

black box The ability stems from

de-velopments in imaging technology thatthe past few years have seen, most no-tably positron-emission tomographyand magnetic resonance imaging Cou-pled with powerful computers, thesetechniques can now capture in real timeimages of the physiology associatedwith thought processes They show howspeciÞc regions of the brain Òlight upÓwhen activities such as reading are per-formed and how neurons and their elab-orate cast of supporting cells organizeand coordinate their tasks The map-ping of thought can also act as a tool forneurosurgery and elucidate the neuraldiÝerences of people crippled by dev-astating mental illnesses, including de-

pression and schizophrenia

I hasten to point out thatthe underlying assumptions

of current brain mapping aredistinct from those held byearly phrenologists They pos-ited that single areas of thebrain, often identiÞed bybumps on the skull, uniquelyrepresented speciÞc thoughtprocesses and emotions Incontrast, modern thinking

posits that networks of neurons ing in strictly localized areas performthought processes So just as speciÞcmembers of a large orchestra performtogether in a precise fashion to pro-duce a symphony, a group of localizedbrain areas performing elementary op-erations work together to exhibit anobservable human behavior The foun-dation for such analyses is that com-plex behaviors can be broken down into

resid-a set of constituent mentresid-al operresid-ations

In order to read, for example, one mustrecognize that a string of letters is aword; then recognize the meaning ofwords, phrases or sentences; and Þnal-

ly create mental images

The challenge, of course, is to mine those parts of the brain that areactive and those that are dormant dur-ing the performance of tasks In thepast, cognitive neuroscientists have re-lied on studies of laboratory animalsand patients with localized brain in-juries to gain insight into the brainÕsfunctions Imaging techniques, howev-

deter-er, permit us to visualize safely theanatomy and the function of the nor-mal human brain

Visualizing the Mind

Strategies of cognitive science and techniques

of modern brain imaging open a window

to the neural systems responsible for thought

by Marcus E Raichle

ACTIVE NEURAL AREAS from a subject remembering a sequence of ters are mapped by magnetic resonance imaging The images below rep-resent six slices through the frontal cortex The slices are identiÞed bynumbers in the corners that correspond to those in the scan at the left.Red, orange and yellow represent areas of increasing activity Jonathan

let-D Cohen and his colleagues at the University of Pittsburgh and negie Mellon University formed the images

Car-6 5 4 3 2 1

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The modern era of medical imaging

began in the early 1970s, when the

world was introduced to a remarkable

technique called x-ray computed

tomog-raphy, now known as x-ray CT, or just

CT South African physicist Allan M

Cor-mack and British engineer Sir Godfrey

HounsÞeld independently developed

its principles HounsÞeld constructed

the Þrst CT instrument in England Both

investigators received the Nobel Prize

in 1979 for their contributions

Computed tomography takes

advan-tage of the fact that diÝerent tissues

absorb varying amounts of x-ray

ener-gy The denser the tissue, the more it

absorbs A highly focused beam of

x-rays traversing through the body will

exit at a reduced level depending on

the tissues and organs through which

it passed A beam of x-rays passed

through the body at many diÝerent

an-gles through a plane collects suÛcient

information to reconstruct a picture of

the body section Crucial in the

devel-opment of x-ray CT was the emergence

of clever computing and mathematical

techniques to process the vast amount

of information necessary to create

im-ages themselves Without the

availabil-ity of sophisticated computers, the

task would have been impossible to

accomplish

X-ray CT had two consequences

First, it changed forever the practice of

medicine because it was much superior

to standard x-rays For the Þrst time,

investigators could safely and

eÝective-ly view living human tissue such as the

brain with no discomfort to the patient

Standard x-rays revealed only bone and

some surrounding soft tissue Second,

it immediately stimulated scientists and

engineers to consider alternative ways

of creating images of the bodyÕs interior

using similar mathematical and

comput-er strategies for image reconstruction

One of the Þrst such groups to be

in-trigued by the possibilities opened by

computed tomography consisted of

ex-perts in tissue autoradiography, a

meth-od used for many years in animal

stud-ies to investigate organ metabolism and

blood ßow In tissue autoradiography,

a radioactively labeled compound is jected into a vein After the compoundhas accumulated in the organ (such asthe brain) under interest, the animal issacriÞced and the organ removed forstudy The organ is carefully sectioned,and the individual slices are laid on apiece of Þlm sensitive to radioactivity

in-Much as the Þlm in a camera records ascene as you originally viewed it, this x-ray Þlm records the distribution of ra-dioactively labeled compound in eachslice of tissue

Once the x-ray Þlm is developed, entists have a picture of the distribu-tion of radioactivity within the organand hence can deduce the organÕs spe-ciÞc functions The type of information

sci-is determined by the radioactive pound injected A radioactively labeledform of glucose, for example, measuresbrain metabolism because glucose is theprimary source of energy for neurons

com-Louis SokoloÝ of the National Institute

of Mental Health introduced this nowwidely used autoradiographic method

real-ly administered radioisotope One hadsimply to measure the emission of ra-dioactivity from the body section Withthis realization was born the idea of au-toradiography of living human subjects

A crucial element in the evolution ofhuman autoradiography was the choice

of radioisotope Workers in the Þeld

se-lected a class of radioisotopes that emitpositrons, which resemble electrons ex-cept that they carry a positive charge

A positron would almost immediatelycombine with a nearby electron Theywould annihilate each other, emittingtwo gamma rays in the process Becauseeach gamma ray travels in nearly oppo-site directions, devices around the sam-ple would detect the gamma rays andlocate their origin The crucial role ofpositrons in human autoradiographygave rise to the name positron-emis-sion tomography, or PET [see ÒPositron-Emission Tomography,Ó by Michel M.Ter-Pogossian, Marcus E Raichle andBurton E Sobel; SCIENTIFIC AMERICAN,October 1980]

Throughout the late 1970s and

early 1980s, researchers rapidlydeveloped PET to measure vari-ous activities in the brain, such as glu-cose metabolism, oxygen consumption,blood ßow and interactions with drugs

Of these variables, blood ßow hasproved the most reliable indicator ofmoment-to-moment brain function.The idea that local blood ßow is inti-mately related to brain function is a sur-prisingly old one English physiologistsCharles S Roy and Charles S Sherring-ton formally presented the idea in apublication in 1890 They suggestedthat an Òautomatic mechanismÓ regu-lated the blood supply to the brain Theamount of blood depended on local var-iations in activity Although subsequentexperiments have amply conÞrmed theexistence of such an automatic mecha-nism, no one as yet is entirely certainabout its exact nature It obviously re-mains a challenging area for research

MARCUS E RAICHLE is professor of neurology, radiology and neurobiology as well as

a senior fellow of the McDonnell Center for Studies of Higher Brain Function at theWashington University School of Medicine in St Louis He received his B.S and M.D de-grees from the University of Washington in Seattle He began researching brainmetabolism and circulation when he was a neurology resident at the New York Hospi-talÐCornell Medical Center His current focus is the use of positron-emission tomogra-phy and magnetic resonance imaging to study human cognition and emotion

Trang 35

PET measures blood ßow in the

nor-mal human brain by adapting an

auto-radiographic technique for laboratory

animals developed in the late 1940s by

Seymour S Kety of the National

Insti-tute of Mental Health and his colleagues

PET relies on radioactively labeled

wa-terĐspeciÞcally, hydrogen combined

with oxygen 15, a radioactive isotope ofoxygen The labeled water emits copi-ous numbers of positrons as it decays(hydrogen isotopes cannot be used, be-cause none emit positrons) The labeledwater is administered into a vein in the

arm In just over a minute the tive water accumulates in the brain,forming an image of blood ßow.The radioactivity of the water pro-duces no deleterious eÝects Oxygen 15has a half-life of only two minutes; an

radioac-60 SCIENTIFIC AMERICAN April 1994

BRAIN SECTION (a ) is compared with

corresponding images of the slice taken

by x-ray computed tomography ( CT )

(b ), positron-emission tomography

( PET ) (c ) and magnetic resonance

imag-ing ( MRI ) (d ) CT depicts the features of

the brain section, whereas PET shows

the amount of neuronal work (the

dark-er the area, the greatdark-er the activity)

Properly set up, MRI can do both tasks

Here it images structure

PET SCANS show active neural areas In the far left column

the left side of the brain is presented; the next columns show

Þve horizontal layers (the right side faces to the right, with

the front to the top) Each row corresponds to the diÝerence

between a speciÞc task and the control state of gazing at a

dot on a television monitor When subjects passively view

nouns (a ), the primary visual cortex lights up When nouns are heard (b ), the temporal lobes take command Spoken nouns minus viewed or heard nouns (c ) reveal motor areas used for speech Generating verbs (d ) requires additional

neural zones, including those in the left frontal and temporallobes corresponding roughly to BrocaÕs and WernickeÕs areas

Trang 36

entire sample decays almost

complete-ly in about 10 minutes (Þve half-lives)

into a nonradioactive form The rapid

decay substantially reduces the

expo-sure of subjects to the potentially

harm-ful eÝects of radiation Moreover, only

low doses of the radioactive label are

necessary

The fast decay and small amounts

permit many measurements of blood

ßow to be made in a single experiment

In this way, PET can take multiple

pic-tures of the brain at work Each picture

serves as a snapshot capturing the

mo-mentary activity within the brain

Typi-cal PET systems can locate changes

in activity with an accuracy of a few

millimeters

A distinct strategy for the functional

mapping of neuronal activity by PET has

emerged during the past 10 years This

approach extends an idea Þrst

intro-duced to psychology in 1868 by Dutch

physiologist Franciscus C Donders

Donders proposed a general method to

measure thought processes based on a

simple logic He subtracted the time

needed to respond to a light (with, say,

the press of a key) from the time

need-ed to respond to a particular color of

light He found that discriminating color

required about 50 milliseconds In this

way, Donders isolated and measured a

mental process for the Þrst time

The current PET strategy is designed

to accomplish a similar subtraction but

in terms of the brain areas

implement-ing the mental process In particular,

im-ages of blood ßow taken before a task

is begun are compared with those

ob-tained when the brain is engaged in that

task Investigators refer to these two

pe-riods as the control state and the task

state Workers carefully choose each

state so as to isolate as best as possible

a limited number of mental operations

Subtracting blood-ßow measurements

made in the control state from each

task state indicates those parts of the

brain active during a particular task

To achieve reliable data, workers take

the average of responses across many

individual subjects or of many

experi-mental trials in the same person aging enables researchers to detectchanges in blood ßow associated withmental activity that would otherwise beeasily confused with spurious shifts re-sulting from noise

lan-in the human bralan-in has been the subject

of intense investigation for more than

a century Work began in earnest in

1861, when French physician Pierre PaulBroca described a patient whose dam-aged left frontal lobe destroyed the abil-ity to speak ( To this day, patients whohave frontal lobe damage and have trou-ble speaking are often referred to ashaving BrocaÕs aphasia.) BrocaÕs studies

of language localization were mented by Carl Wernicke, a Germanneurologist In 1874 Wernicke told ofpeople who had diÛculty comprehend-ing language They harbored damage tothe left temporal lobe, a region now usu-ally referred to as WernickeÕs area Fromthese beginnings has emerged a con-cept of language organization in thehuman brain: information ßows fromvisual and auditory reception to areas

comple-in the left temporal lobe for hension and then on to frontal areasfor speech production [see ỊSpecializa-tions of the Human Brain,Ĩ by NormanGeschwind; SCIENTIFIC AMERICAN, Sep-tember 1979 ]

compre-All this information was gleaned frombrain-damaged patients Can investiga-tors derive insight about language orga-nization from a healthy brain? In 1988

my colleagues Steven E Petersen, chael I Posner, Peter T Fox and Mark

Mi-A Mintun and I at the Washington versity Medical Center began a series ofstudies to answer just this question Theinitial study was based on a PET analy-sis of a seemingly simple job: speaking

Uni-an appropriate verb when presentedwith a common English noun For ex-ample, a subject might see or hear the

word Ịhammer,Ĩ to which an ate response might be Ịhit.Ĩ

appropri-We chose this assignment because itcould be broken down into many com-ponents Each component could sepa-rately be analyzed through a careful se-lection of tasks The most readily appar-ent elements include visual and auditoryword perception, the organization andexecution of word output (speech), andthe processes by which the brain re-trieves the meanings of words ( Ofcourse, each of these operations can bedivided further into several additionalsubcomponents.)

To identify the areas of the brain used

in a particular operation, we composedfour levels of information processing.Such a hierarchy has become standardamong laboratories doing this type of

research [see bottom illustration on

op-posite page] In the Þrst level, subjects

were asked to Þx their gaze on a pair

of small crosshairsĐthe arrangementlooks like a small plus signĐin themiddle of a television monitor At thesame time, a PET scan measured bloodßow in the brain, providing a snapshot

of mental activity

In the second level, subjects ued to maintain their gaze on the cross-hairs as blood ßow was measured, butduring this scan they were exposed tocommon English nouns The nouns ei-ther appeared below the crosshairs onthe television monitor or were spokenthrough earphones (separate scans wereperformed for visual and auditory pre-sentations) In the third level, subjectswere asked to recite the word theyviewed or heard Finally, in the fourthlevel, the subjects said out loud a verbappropriate for the noun

contin-Subtracting the Þrst level from thesecond isolated those brain areas con-cerned with visual and auditory wordperception Deducting the second levelfrom the third pinpointed those parts

of the brain concerned with speech duction Subtracting level three fromlevel four located those regions con-cerned with selecting the appropriateverb to a presented noun

pro-The Þnal subtraction (speaking nounsminus generating verbs) was of partic-ular interest, because it provided a por-trait of pure mental activity (perceptionand speechĐor input and outputĐhav-ing been subtracted away) This imagepermitted us to view what occurs in ourbrains as we interpret the meaning ofwords and, in turn, express meaningthrough their use It renders visible con-scious function because much of ourthinking is carried out by concepts andideas represented by words

The results of this study clearly onstrate how brain imaging can relate

Trang 37

dem-mental operations of a behavioral task

to speciÞc networks of brain areas

or-chestrated to perform each operation

As anticipated by cognitive scientists

and neuroscientists, the apparently

sim-ple task of generating a verb for a

pre-sented noun is not accomplished by a

single part of the brain but rather by

many areas organized into networks

Perception of visually presented wordsoccurs in a network of areas in the back

of the brain, where many components

of the brainÕs visual system reside ception of aurally presented words oc-curs in an entirely separate network ofareasĐin our temporal lobes

Per-Speech production (that is, simply peating out loud the presented nouns)

re-predictably involves motor areas of thebrain Regions thought to be BrocaÕs andWernickeÕs areas do not appear to beengaged routinely in this type of speechproduction, an activity that would beviewed by many as quite automatic formost ßuent speakers in their nativelanguage This Þnding suggests what

we might have suspected : we ally speak without consciously thinkingabout the consequences

occasion-Regions of the left frontal and poral lobes (those corresponding in gen-eral to the respective locations of Bro-caÕs and WernickeÕs areas) only becomeactive when two tasks are added : con-sciously assessing word meaning andchoosing an appropriate response.Moreover, two other areas come intoplay under these circumstances, form-ing a network of four brain regions In-terestingly, two areas used in the rou-tine repetition of words were turned

tem-oÝ This shutdown suggests that thedemands of generating a verb to a pre-sented noun does not simply build onthe task of just saying the noun Ratherthe act of speaking a verb to a present-

ed noun diÝers from speaking thenoun, as far as the brain is concerned.This Þnding caused us to pause andconsider what would happen if we al-lowed subjects a few minutes of prac-tice on their task of generating verbs.Although subjects initially discover thatforming verbs rapidly is diÛcult (nounsare presented every 1.5 seconds), theybecome relaxed and proÞcient after 15minutes of practice An examination

of the brain after training reveals thatpractice completely changes the neural

circuits recruited [ see top illustration on

this page ] The circuits responsible for

noun repetition now generate theverbs Thus, practice not only makesperfect (something we have alwaysknown) but also changes the way ourbrain organizes itself (something wemay not have fully appreciated )

As cognitive neuroscientists

dem-onstrated the utility of PET nology, a newer method swiftlyemerged that could compete with PETÕsabilities Magnetic resonance imaging,

tech-or MRI, has now become a fairly mon tool for diagnosing tissue damage.Recent developments have vastly in-creased the speed with which MRI canform images, thus making it suitablefor research in cognitive neuroscience.MRI derives from a potent laboratorytechnique known as nuclear magneticresonance ( NMR ), which was designed

com-to explore detailed chemical features ofmolecules It garnered a Nobel Prize forits developers, Felix Bloch of StanfordUniversity and Edward M Purcell of

LEARNING-INDUCED CHANGES in neural activity are revealed by PET imaging The

top row shows the brain of a subject who must quickly generate verbs appropriate

to visually presented nouns The bottom row shows the result of 15 minutes of

prac-tice; the regions activated are similar to those used in simply reading out loud

IMAGE SUBTRACTION AND AVERAGING serve as the foundation of functional

brain imaging Researchers subtract the PET blood-ßow pattern of a control state

from that of a task state to produce a diÝerence image (top row ) Data from

diÝer-ent subjects are averaged (bottom two rows ) to eliminate statistical ßuctuations.

TASK STATE CONTROL STATE

INDIVIDUAL DIFFERENCE IMAGES

MEAN DIFFERENCE IMAGE

Trang 38

Harvard University, in 1952 The method

depends on the fact that many atoms

behave as little compass needles in the

presence of a magnetic Þeld By

skillful-ly manipulating the magnetic Þeld,

sci-entists can align the atoms Applying

radio-wave pulses to the sample under

these conditions perturbs the atoms in

a precise manner As a result, they emit

detectable radio signals unique to the

number and state of the particular

atoms in the sample Careful

adjust-ments of the magnetic Þeld and the

ra-dio-wave pulses yield particular

infor-mation about the sample under study

NMR moved from the laboratory to

the clinic when Paul C Lauterbur of the

University of Illinois found that NMR

can form images by detecting protons

Protons are useful because they are

abundant in the human body and, by

acting as little compass needles,

re-spond sensitively to magnetic Þelds

Their application resulted in excellent

images of the anatomy of organs that

far surpassed in detail those produced

by x-ray CT [see ÒNMR Imaging in

Medicine,Ó by Ian L Pykett; SCIENTIFIC

AMERICAN, May 1982] Because the term

ÒnuclearÓ made the procedure sound

dangerous, NMR soon became known

as magnetic resonance imaging

The current excitement over MRI for

brain imaging stems from the

tech-niqueÕs ability to detect a signal

inacces-sible to PET scans SpeciÞcally, it can

detect an increase in oxygen that

oc-curs in an area of heightened

neuro-nal activity The basis for this capacity

comes from the way neurons make use

of oxygen PET scans had revealed that

functionally induced increases in blood

ßow accompanied alterations in the

amount of glucose the brain consumed

but not in the amount of oxygen it used

In eÝect, the normal human brain

dur-ing spurts of neuronal activity resorts

to anaerobic metabolism Few had

sus-pected that the brain might rely on

tac-tics similar to those used by sprinterÕs

muscles In fact, this form of

metabo-lism occurs despite the presence of

abundant oxygen in the normal brain

Why the brain acts this way is a mystery

worthy of intense scientiÞc scrutiny

Additional blood to the brain without

a concomitant increase in oxygen

sumption leads to a heightened

con-centration of oxygen in the small veins

draining the active neural centers The

reason is that supply has increased, but

the demand has not Therefore, the

ex-tra oxygen delivered to the active part

of brain simply returns to the general

circulation by way of the draining veins

Why does oxygen play a crucial role

in MRI studies of the brain? The answer

lies in a discovery made by Nobel

laure-ate Linus C Pauling in 1935 He foundthat the amount of oxygen carried byhemoglobin (the molecule that trans-ports oxygen and gives blood its redcolor ) aÝects the magnetic properties

of the hemoglobin In 1990 Seiji Ogawaand his colleagues at AT&T Bell Labora-tories demonstrated that MRI could de-tect these small magnetic ßuctuations

Several research groups immediatelyrealized the importance of this obser-vation By the middle of 1991 investi-gators showed that MRI can detect thefunctionally induced changes in bloodoxygenation in the human brain Theability of MRI machines to detect func-tionally induced changes in blood oxy-genation leads many to refer to thetechnique as functional MRI, or fMRI

Functional MRI has several tages over x-ray CT and other imagingtechniques First, the signal comes di-rectly from functionally induced chang-

advan-es in the brain tissue (that is, the change

in venous oxygen concentration) ing, radioactive or otherwise, needs to

Noth-be injected to obtain a signal Second,MRI provides both anatomical and func-tional information in each subject, hence

permitting an accurate structural tiÞcation of the active regions Third,the spatial resolution is quite good, dis-tinguishing parts as small as one to twomillimeters (better than PETÕs resolu-tion) Fourth, when properly equipped(that is, given so-called echoplanar ca-pability), MRI can monitor the rate ofchange in the blood-ßow-induced oxy-

iden-gen signal in real time [see illustration

below ].

Finally, MRI has little, if any, knownbiological risk Some workers haveraised concerns about the intensity ofthe magnetic Þeld to which the tissuesare exposed So far most studies havefound the eÝects to be benign Thelargest drawback is the claustrophobiasome subjects may suÝer In most in-strument designs the entire body must

be inserted into a relatively narrow tube.Several intriguing results with func-tional MRI were reported this past year.Robert G Shulman and his colleagues

at Yale University have conÞrmed PETÞndings about language organization

in the brain Using conventional, tal-based MRI, Walter Schneider andJonathan D Cohen and their colleagues

hospi-BLOOD FLOW to the brain provides the signals detected by functional MRI and

PET When resting neurons (top ) become active (bottom ), blood ßow to them creases MRI (left ) detects changes in oxygen levels, which rise in the nearby blood

in-vessels because active neurons consume no more oxygen than when they are at

rest PET (right ) relies on the increased delivery of injected radioactive water,

which diÝuses out of the vessels to reach all parts of the brain

RADIOACTIVEWATER

Trang 39

at the University of Pittsburgh have

cor-roborated work in monkeys that

indi-cated the primate visual cortex is

orga-nized into topographic maps that

re-ßect the spatial organization of the

world as we see it Other groups are

ac-tively trying to visualize other forms of

mental activity, such as the way we

cre-ate mental images and memories

The ability of MRI systems to

mon-itor the oxygen signal in real time

has suggested to some the

possi-bility of measuring the time it takes for

diÝerent brain areas to exchange

infor-mation Conceptually, one might think

of a network of brain areas as a group

of individuals in the midst of a

confer-ence call The temporal information

sought would be equivalent to knowing

who was speaking when and, possibly,

who was in charge Such information

would be critical in understanding how

speciÞc brain areas coordinate as a

net-work to produce behavior

The stumbling block, however, is the

speed of neuronal activity compared

with the rate of change of oxygenation

levels Signals from one part of the brain

can travel to another in 0.01 second or

less Unfortunately, changes in blood

ßow and blood oxygenation are much

slower, occurring hundreds of

millisec-onds to several secmillisec-onds later MRI

would not be able to keep up with the

ÒconversationsÓ between brain areas

The only methods that respond quickly

enough are electrical recording

tech-niques Such approaches include

elec-troencephalography ( EEG ), which

de-tects brain electrical activity from the

scalp, and magnetoencephalography( MEG ), which measures the magneticÞelds generated by electrical activitywithin the brain

Why donÕt researchers just use EEG

or MEG for the whole job of mappingbrain function? The limitations arespatial resolution and sensitivity Eventhough great strides in resolution have

been made, especially with MEG [see

il-lustration above ], accurate localization

of the source of brain activity remainsdiÛcult with electrical recording de-vices Furthermore, the resolution be-comes poorer the deeper into the brain

we attempt to image

Neither MRI nor PET suÝers fromthis diÛculty They both can sample allparts of the brain with equal spatialresolution and sensitivity As a result, acollaboration seems to be in the mak-ing between PET and MRI and electricalrecording PET and MRI, working in acombination yet to be determined, candeÞne the anatomy of the circuits un-derlying a behavior of interest; electri-cal recording techniques can reveal thecourse of temporal events in these spa-tially deÞned circuits

Regardless of the particular mix oftechnologies that will ultimately be used

to image human brain function, theÞeld demands extraordinary resources

Expensive equipment dominates thiswork MRI, PET and MEG equipmentcosts from $2 million to $4 million and

is expensive to maintain Furthermore,success requires close collaborationwithin multidisciplinary teams of sci-entists and engineers working dailywith these tools Institutions fortunate

enough to have the necessary technicaland human resources need to makethem available to scientists at institu-tions less fortunate Although some ra-diology departments have such equip-ment, the devices are usually commit-ted mostly for patient care

In addition to the images of brain tivity, the experiments provide a vastamount of information Such an accu-mulation not only yields answers to thequestions posed at the time of the ex-periment but also provides invaluableinformation for future research, asthose of us in the Þeld have repeatedlydiscovered to our amazement and de-light Recent eÝorts to create neuro-science databases could organize andquickly disseminate such a repository

ac-of information

Wise use of these powerful new toolsand the data they produce can aid ourunderstanding and care of people whohave problems ranging from develop-mental learning disorders to languagedisabilities arising from, say, stroke Re-searchers have begun to use functionalbrain imaging to learn about the mooddisturbances that aÜict patients withsuch mental illnesses as depression.The technology could guide neurosur-geons in the excision of brain tumors,enabling them to judge how the remov-

al of tissue will hamper the patient.Centers across the world are investigat-ing such other mental activities as at-tention, memory, perception, motorcontrol and emotion Clearly, we areheaded toward a much richer grasp ofthe relation between the human mindand the brain

FURTHER READINGINTRINSIC SIGNAL CHANGES ACCOMPANY-ING SENSORY STIMULATION: FUNCTION-

AL BRAIN MAPPING WITH MAGNETIC ONANCE IMAGING S Ogawa, D W Tank,

RES-R Menon, J M Ellermann, S.-G Kim,

H Merkle and K Ugurbil in Proceedings

of the National Academy of Sciences,

Vol 89, No 13, pages 5951Ð5955; July

1, 1992

SOMATOSENSORY CORTICAL PLASTICITY

IN ADULT HUMANS REVEALED BY NETOENCEPHALOGRAPHY A Mogilner et

MAG-al in Proceedings of the National Academy of Sciences, Vol 90, No 8,

pages 3593Ð3597; April 15, 1993

IMAGES OF MIND M I Posner and M E.Raichle W H Freeman and Company,1994

PRACTICE-RELATED CHANGES IN HUMAN

FUNCTIONAL ANATOMY DURING MOTOR LEARNING M E Raichle, J A.Fiez, T O Videen, A.-M K MacLeod,

NON-J V Pardo, P T Fox and S E Petersen

in Cerebral Cortex, Vol 4, No 1, pages

8Ð26; January/February 1994

MAGNETOENCEPHALOGRAPHY, or MEG,

cap-tures neural activity too brief to be detected by

PET or MRI Above, MEG has located the areas

in the normal adult somatosensory cortex

as-sociated with the digits of the right hand

(col-ored symbols ) The symbols on the MRI image

of the brain correspond to those on the Þngers

Trang 40

Interest in the application of science

to the art of cookery is growing

Cooks once regarded the

introduc-tion of scientiÞc reasoning, let alone

laboratory techniques, into their

kitch-ens with suspicion, even with hostility

That time seems to be past

Neverthe-less, both in restaurants and in

domes-tic kitchens, many cooks tend to

re-main faithful to the grand culinary

tra-ditions and practices they were taught,

without knowing why (or really even

whether ) those practices guarantee the

best results Thus, cooks add pinches

of ßour when heating custards to

pre-vent them from curdling; they rigidly

follow certain protocols in making

soufflŽs; they generally do not vary the

proportions of ingredients in their

recipes, and so on Perhaps for that

reason, culinary superstitions and old

wivesÕ tales continue to ßourish

The mistrust of scientiÞc explanations

for culinary mysteries is all the moresurprising given that music, painting,sculpture and the performing arts haveprospered with experimental scrutinyand discovery Science has improvedthe technologies for preserving, repro-ducing and disseminating works of art,which has led to a greater appreciation

of those works by a wider audience

There is no proof that science and nology have compromised creativity inany way; they may even have helped it

tech-We believe it is the duty of scientists

to acquaint culinary artists with ples and techniques that may stimulatetheir imagination, just as they have pre-viously done for painters, composersand musicians The time seems ripe forsuch an approach Physics is beginning

princi-to explore the state of emulsions, pensions, solid dispersions and foamsĐỊsoft matter,Ĩ as physics Nobelist Pierre-Gilles de Gennes has called themĐthatoften occur in cooking Advanced struc-tural chemistry can now elucidate thebehavior of large molecules such ascomplex carbohydrates and proteins

sus-New chromatographic methods make

it possible to isolate the components offoods that give rise to tastes and smells

ScientiÞc explanations are already pearing for many old and seemingly ob-scure culinary tricks

ap-In eÝect, a new discipline is beingborn: molecular and physical gastrono-

my, the science of food and its ment We would like to oÝer a smallfeast of discoveries from this ÞeldĐconcerning appetizers, main courses,desserts and beveragesĐthat may be

enjoy-of practical value and interest to cooks

Several of our examples are drawn fromdiscussions at the First InternationalWorkshop on Molecular and PhysicalGastronomy, which we organized inAugust 1992 in Erice, Sicily

A popular Þrst course, oeuf dur

may-onnaise (hard-boiled egg with

mayon-naise), gives us the opportunity to amine the molecular and physicalproperties of emulsions Mayonnaise,cream, butter and bŽarnaise sauce areall emulsions, in which droplets of oneliquid are suspended in another withwhich it is immiscible

ex-Mayonnaise consists of

vegeta-ble oil, vinegar or lemon juice,and egg yolk Because half theyolk is water, mayonnaise is actually anemulsion of oil in water Ordinarily, nomatter how thoroughly you whisk amixture of water and oil, the two com-ponents separate into distinct layers.Mayonnaise is stable because the eggyolk contains so-called surface-activemolecules such as lecithins The twoends of these rod-shaped moleculeshave different properties: one is hydro-philic ( it has an aÛnity for water ), andthe other is hydrophobic ( it shuns wa-ter ) Each oil globule in the mayonnaise

Chemistry and Physics

in the Kitchen

Bon appŽtit! Scientists are beginning to understand how chefs accomplish their culinary masterpieces—

and are making modest recipe suggestions of their own

by Nicholas Kurti and HervŽ This-Benckhard

NICHOLAS KURTI and HERVƒ

THIS-BENCKHARD have collaborated in the

new field of molecular and physical

gas-tronomy since 1989 Kurti, emeritus

pro-fessor of physics at the University of

Ox-ford and a former vice president of the

Royal Society, was born in 1908 and

ed-ucated at the University of Paris and the

University of Berlin During his long

ca-reer, he has achieved many honors,

in-cluding election as an honorary member

of the American Academy of Arts and

Sciences His many papers and books

cover topics in cryophysics, magnetism,

energy and, more recently, culinary

phys-ics This-Benckhard is the co-editor of

Pour la Science, the French edition of

Sci-entific American He has written

exten-sively about chemistry, mathematics and

culinary science He holds a degree in

physical chemistry from the ƒcole

SupŽ-rieure de Physique et de Chimie

Indus-trielles de Paris and has studied modern

literature at the University of Paris

INSTANT ICE CREAM, produced by thevaporization of liquid nitrogen, is one

of the culinary delights being created

by a hitherto unused technique Thejoint eÝorts of scientists and cooks areexplaining why certain cooking practic-

es work and, in some cases, how theycan be improved

Tiêu đề	The Dilemmas of Prostate Cancer
Tác giả	Marc B. Garnick
Chuyên ngành	Medicine / Oncology
Thể loại	article
Năm xuất bản	1994
Thành phố	New York

Định dạng
Số trang	93
Dung lượng	7,13 MB