8/8/2019 HIV Attacks Gut First

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30ASTRONOMY—Sightings of 

shifting sand dunes,rolling boulders, and adwindling polar ice capin the past year demon-strate that the RedPlanet is a far more dy-namic world than sci-entists suspected.

NASA’s orbiting MarsGlobal Surveyor revealedfresh gullies as long asthree football fields on adune west ofthe HellasBasin. The same slopewas smooth and un-blemished in 2002. Sci-entists suspect thatcarbon dioxide trappedbeneath the surface dur-

ing winter vaporizedwhen temperatures rose,releasing gas and causingsand to pour down thedune’s face. The probealso photographeddozens ofboulders thathad tumbled down a five-mile-wide crater, goug-

ing shallow troughs not

seen a year before.Possi-ble causes include windand seismic activity, al-though Mars’s atmos-phere is justone-hundredth as denseas Earth’s,and researchershave not yet found reli-able evidence of Marsquakes.Meanwhile,carbon dioxide depositsat the south pole havedwindled for three con-secutive summers, sug-gesting long-term climatechange is under way.

None of these sight-ings would be possible if not for the extraordinary 

durabi li ty of M arsGlobal Surveyor, whichhas been orbiting theplanet since 1997.Mean-while,the Opportunity and Spirit rovers,whichlanded in January 2004,have kept rolling longpast their predicted shelf 

life of90 days.In Sep-

tember Spirit completeda 14-month climb upHusband Hill in Gusev Crater and sent back apanorama of weatheredrocks containing detailsof past Mars environ-ments. “Everyone isamazed at the longevity,excited about the results,and perhaps a littletired,” says MichaelMeyer, chiefscientist of NASA’s Mars Explo-ration Program.

Next up:the Mars Re-connaissance Orbiter,launched last August 12,enters Mars orbit in

March. Its radar sounderwill seek buried water,while its camera willmap features as small asa coffee table,aiding thesearch for potential habi-tats of past or presentlife.“Stay tuned,” saysMeyer. — Jack Kelley 

Mars Looks Lively

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2D I S COV E R J A NUA RY 2006

PSYCHOLOGY—Patientswho have suffered strokeor head injuries oftenlose the ability to makegood decisions.For in-stance, they will make re-peated bets on aparticular outcome,evenwhen the odds of win-ning are obviously very low.In July Michael Sad-doris,a psychology grad-uate student at JohnsHopkins University,helped pinpoint why.

Previous studies sug-gested that the abnor-

malities occurred in abrain area known as theorbital frontal cortex.

To test how this partof the brain functionsduring decisionmaking,Saddoris and his collab-orators presented a taskto a group of normal rats

and a group with dam-age in this region:Bothgroups had to figure outwhich oftwo differentodors led to a sugary treat and which to a bit-ter one.“It’s like if yousaw a soda machine withforeign writing on it,”Saddoris explains.“Youmight push one buttonand get something really odd,so you wouldn’t try that again.But if youcame back the next day and got something youreally liked,you’d push

that button again andagain.”In the same way,the animals had to learnto use the smell cue topredict a particular out-come.

The next step was toreverse the cues for thesweet and salty sub-

stances,then see howlong it took for the ratsto catch on.Those withdefective brain circuitry had much more diffi-culty figuring it out.Datafrom electrodes im-planted into their brainsoffered a clue: Neuronsin the impaired rats firedless in the presence of odors.They weren’t ableto monitor the new cir-cumstances and formnew associations.

Understanding howthe orbital frontal cor-

tex influences judgmentmay lead to therapies.“We’re not at the level of using neuroprostheticsor implants to affect de-cision making yet,but itmight be possible to getthere,”Sadd oris says.

—Elizabeth Svoboda 

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1 D I S COV E R J A NUA RY 2005

driving simulator to mea-sure reaction times,psy-chologist David Strayerfound teenagers have thegreatest trouble combin-ing driving and talking,but the problem affects

all generations.“We seethat accident rates, if  you’re using a cell phone,are about four timesgreater than if you’re notusing a cell phone,” hesays.“Cell phones seemto be a distraction acrossthe age range.”

—Kurt Repanshek 

TECHNOLOGY—High-techgadgets make it possiblefor people to travelthrough time .. .well,sortof.To leap forward 40 to50 years,merely talk ona cell phone while cruis-

ing down the road.Re-search at the University of Utah shows that whendrivers between 18 and25 chat on a cell phone,their reactions to a brak-ing car resemble those of a 65- to 74-year-old mo-torist with no such dis-tractions.Employing a

86Cell Phones Simulate Premature Aging

Why StrokeVictims Can’t Make

Good Decisions54

MEDICINE—For more than a

decade,scienti sts have tracked

the insidious progression of HIV

by measuring the amount of virus

in a patient’s blood.Over a pe-riod of years,the replication of

the virus gradually and steadily

destroys the immune system’s

defenses—or so it was thought.

In April two studies of simian im-

munodeficiency virus, a kin of

HIV that infects monkeys, re-

ported that the virus swiftly in-

fects and decimates key immune

cells in the gut within days,not

years,of infection.“This basically

changes our whole view of the

pathogenesis of HIV infection,”

says Daniel Douek,chief of the

Human Immunology Section at

the National Institutes of Health’s

 Vaccine Research Center.

 Virologists have long known

that HIV infects and kills CD4+T cells,which mediate the body’s

immune response to viruses.

What has emerged over the past

few years is that the virus thrives

not only in the blood and the

lymph system but also in mu-

cosal tissues, which are rich in

immune cells.The mucosae line

parts of the body,such as themouth,nose, and rectum,that

are exposed to the environment.

The gut,the largest of the mu-

cosal tissues,harbors most of

the body’s CD4+ T cells.

“What we now know is that

within the first few weeks of in-

fection,probably two to three

weeks,the majority of those cells

are depleted by HIV infection,”

says Douek.About half the T cells

were wiped out over just four

days within the first two weeks

of infection..

The findings have profound

implications for the control of HIV

infection.These results under-

score the importance of starting

antiretroviral therapy very earlyin the infection. And they high-

light the importance of a vac-

cine that can protect mucosal

surfaces.— Apoorva Mandavilli 

HIV AttacksGut First

HIV-positive gut (top) lacks immune cells seen in HIV-free gut.

Tests on simulators show that the likelihood of accidents increases if a driver is multitasking.Fresh gullies have appeared in dunes inside this Martian crater within the past three years.

PLEASE FILLOUT CAPTION.

Which tie will it be today? Ask your orbital frontal cortex.

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