2
3 0 ASTRONOMY—Sightings of shifting sand dunes, rolling boulders, and a dwindling polar ice cap in the past year demon- strate that the Red Planet is a far more dy- namic world than sci- entists suspected. NASA’s orbiting Mars Global Surveyor revealed fresh gullies as long as three football fields on a dune west ofthe Hellas Basin. The same slope was smooth and un- blemished in 2 002. Sci- entists suspect that carbon dioxide trapped beneath the surface dur- ing winter vaporized when temperatures rose, releasing gas and causing sand to pour down the dune’s face. The probe also photographed dozens ofboulders that had tumbled down a five- mile-wide crater, goug- ing shallow troughs not seen a year before.Possi- ble causes include wind and seismic activity, al- though Mars’s atmos- phere is just one-hundredth as dense as Earth’s,and researchers have not yet found reli- able evidence of Marsquakes.Meanwhile, carbon dioxide deposits at the south pole have dwindled for three con- secutive summers, sug- gesting long-term climate change is under way. None of these sight- ings would be possible if not for the extraordinary durability of Mars Global Surveyor, which has been orbiting the planet since 1997.Mean- while,the Opportuni ty and Spirit rovers,which landed in January 2004, have kept rolling long past their predicted shelf life of90 days.In Sep- tember Spirit completed a 14-month climb up Husband Hill in Gusev Crater and sent back a panorama of weathered rocks containing details of past Mars envir on- ment s. “Ev eryone is amazed at the longevity, excited about the results, and perhaps a little tire d, says Michael Meyer , 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 sounder will seek buried water, while its camera will map features as small as a coffee table,aiding the search for potential habi- tats of past or present life.“Stay tuned, says Meyer.  Jack Kelley Mars Looks Lively 4 6 M C K Y 2 DISCOVER JANUARY 2006 PSYCHOLOGY—Patients who have suffered stroke or head injuries often lose the ability to make good decisions.For in- stance, they will make re- peated bets on a particula r outcom e,even when the odds of win- ning are obviously very low.In July Michael Sad- doris,a psychology grad- uate student at Johns Hopkins University, helped pinpoint why. Previous studies sug- gested that the abnor- malities occurred in a brain area known as the orbital frontal cortex. To test how this part of the brain functi ons during decisionmaking, Saddoris and his collab- orators presented a task to a group of normal rats and a group with dam- age in this region:Both groups had to figure out which oftwo different odors led to a sugary treat and which to a bit- ter one.“It’s like if you saw a soda machine with foreign writing on it,” Saddoris explains.“You might push one button and get something really odd,so you wouldn’t try that ag ain.But if you came back the next day and got something you really liked,you’d push that button again and again.”In the same way, the animals had to learn to use the smell cue to predict a particular out- come. The next step was to reverse the cues for the sweet and salty sub- stances,then see how long it took for the rats to catch on.Those with defective brain circuitry had much more diffi- culty figuring it out.Data from electrodes im- planted into their brains offered a clue: Neuron s in the impaired rats fired less in the presence of odors.They weren’t able to monitor the new cir- cumstances and form new associations. Understanding how the orbital frontal cor- tex influences judgment may lead to therapies. “We’re not at the level of using neuroprosthetics or implants to affect de- cision making yet,but it might be possible to get there,”Sadd oris says. Elizabeth Svoboda M C K Y 1 DISCOVER JANUARY 2005 driving simulator to mea- sure reaction times,psy- chologist David Strayer found teenagers have the greatest trouble combin- ing driving and talking, but the problem affects all generations.“We see that accident rates, if  you’re using a cell phone, are about four times greater than if you’ re not using a cell phone, he says.“Cell phones seem to be a distraction across the age range.” Kurt Repanshek TECHNOLOGY—High-tech gadgets make it possible for people to travel thro ugh time .. .well,sort of.To leap forward 40 to 50 years,merely talk on a cell phone while cruis- ing down the road.Re- search at the University of Utah show s that when drivers between 18 and 25 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 8 6 Cell Phones Simulate Premature Aging Why Stroke Victims Can’t Make Good Decisions 5 4 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- munodeficienc y virus, a kin of HIV that infects mon keys, 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 the mouth,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 early in the infection. And they high- light the importance of a vac- cine that can protect mucosal surfac es.— Apoorva Mandavilli HIV Attacks Gut 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. PAGE PROOF Date ________ AS____ SR____ CSP____ Copy____ JT_ ___ DG____ SLP____ REVERSE AS____ SR____ AB____ JT _____ Copy____ MF_____ AUCX JK_____ AM_____ ES_____ KR_____

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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

46

MC K

Y

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 

M

C KY

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.

PAGE PROOF Date ________

AS____ SR____ CSP____ Copy____ JT_ ___ DG____ SLP____

REVERSE

AS____

SR____ AB____

JT _____ Copy____

MF_____AUCX

JK_____

AM_____

ES_____

KR_____