大学英语四级美文欣赏：饥饿让大脑偏向垃圾食品思维导图

Butwhilethedangeriswellknowntoshopperswhoventureoutonanemptystomach,howtheproblemarisesinthebrainhasremainedamystery.

Inanewstudyofhunger'seffectsonthemind,neuroscientistspiecedtogetherwhathappensinthebrainthatmakesusbuymorefoodwhenwearefamished.

Thefindingspointtowaysofovercomingthetemptationsofthefoodaislesandthrowfreshlightontheriseofobesityoverthepast30years.

Fromaseriesofbrainscansonvolunteers,theresearchersshowedthatahungerhormonetriggeredactivityinthebrainthatmadepeoplepaymoreforjunkfoodthanusual.Equippedwiththisknowledge,shoppersshouldbeabletooverridetheurgeandsticktomorehealthyshopping,thescientistssaid.

"Youshouldnevermakedecisionsaboutfoodwhenyouarestarving.Whenyougotothesupermarkethungry,thefoodyouaredrawntoishigh-caloriejunkfood,"saidDrAlainDagher,aneurologistattheMontrealNeurologicalInstitute."Youassignwaytoomuchvaluetocaloriesandsowaytoolittletohealthandotherthings."

DagherandhiscolleagueDebTangrecruited29volunteersforthestudyand,askedthemtoratehowmuchtheylikedvariousitemsoffood,fromchocolatecookiesandpotatocrispstoapplesandcarrots.

Thescientistsnextputthevolunteersinabrainscannerandhadthembiduptofivedollarsatimeforfoodandotherobjects,suchasbaseballcapsandT-shirts,thatflasheduponascreen.

Aftereachvolunteerhadbidfor300items,onebidwastakenandcomparedwithacounterbidgeneratedatrandombyacomputer.Ifthevolunteerbidthemost,theygottoeatthefoodorkeeptheitematstake.

Eachpersontookthetesttwiceovertwodaysandbeforehandreceivedeitheraninjectionofghrelin,ahungerhormonethatisreleasedbythestomach,orashotofsalineasacontrol.Theghrelinjabmadevolunteersravenousforonetotwohours.

Unsurprisingly,thehungryvolunteersbidconsistentlymoreforfoodandlessforinedibleitemsthanthevolunteerswhohadthesalinejab.Thehungrypeoplewerewillingtospendanaverageof$2.09forfoodand$1.32forotherobjects,butonsalinebidonly$1.82forfoodand$1.58fortheinedibleitems.

Thescientiststracedthebehaviourtoincreasedactivityinabrainregioncalledtheventromedialprefrontalcortex,whichisinvolvedinmotivationandreward.

"Ghrelinseemstoincreasetheamountyouarewillingtopayforfoodthroughthisareaofthebrain.Wethinkthisiswhyyouassigngreatervaluetothefoodwhenyouarehungry,"Daghersaid.TheresearchwaspresentedattheSocietyforNeurosciencemeetinginWashingtonDC.

Butthestudyfoundthatpeopledidnotsimplypaymoreforfoodstheyliked.Instead,thehigherbidswereforthehigh-caloriejunkfoods.

"Whenyouarehungryyouassignwaytoomuchvaluetocaloriesandsowaytoolittletohealthandotherthings,"Daghersaid.

Dagherbelievesthatsimplybeingawareofthewaythebrainworkscouldhelppeopleovercometheurgetobuyjunkfoodwhentheyarehungry."Wehavethisintrinsicvaluesystembutwecanoverrideitwithourminds,"hesaid.

Thefindingssupportevidencethatshowsskippingmealstoloseweightcanbecounterproductive."Ifyoumissmeals,youtendtogainweightbecauseyougethungrierandeatcaloricallydensefoods,"Daghersaid.

"Themainreasonfortheincreaseinobesityoverthepast30yearsisthecostoffood.Whenyoulookatanitemofhigh-caloriefood,itscostislow,soyou'remorelikelytobuyit.Andonceyouhaveboughtit,youaremorelikelytoconsumeit.

"Theproblemisthedecision-makingbeforeyouevensitdowntoyourmeal.That'swhereyouhavelostthebattle,"Daghersaid.

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