2024剑桥雅思讲义Yes_No_NG_Questions_Strategy_Practice.docx

Whatisdopamine-andisittoblameforouraddictions?Thekeydifferencebetweenhumanbrainsandthoseofotheranimalsisthesizeandcomplexityofourcerebralcortex,thebrain'souterlayerofneuraltissue.Wethereforetendtofocusourattentiononthisarea,believingthatouruniquementallifeisduetothismasterpieceofevolution.However,weoftenignorethebitsthatarenearlyidenticalbetweenhumansandanimals,suchasthetinygroupofbraincellsthatusethechemicaldopaminetocommunicatewithotherbraincells.Dopamineisoftendescribedasthebrain,s"pleasurechemica,butitisactuallyinvolvedinalargenumberofphysicalandmentalprocesses.Itisusedbyaclusterofneuronsinthemidbraintotransmitmessagestootherneurons.Thedopamineneuronsaresmallinnumber(0.0006%oftheneuronsinthehumanbrain)andtheyareobservedinallmammalsandevenusimple"animalssuchasturtles.Inthe1950s,researchersdiscoveredthatratsappearedtoenjoythestimulationofthenervebundlethatlinksthedopamineneuronswiththeirtargetsintheforebrain.Theratswouldlearntopressaleverforthiskindofstimulation,and,leftunchecked,woulddosothousandsoftimesinaday.Asimilar(andwhollyunethical)experimentwasperformedin1970onahumanpatient.Liketherats,thepatientlearnedtopressabuttontostimulatethedopaminenervebundle,pressingthebuttonupto1500timesoverthecourseofathree-hoursessionandreportingfeelingsofpleasureduringthestimulation.Sincethen,studieshaveshownthatthedopaminesystemcanbeactivatedbyawiderangeofpleasantexperiences,suchaseating,sexualintercourse,gettingrevenge,winningvideogames,listeningtomusic,earningmoneyandreadingfunnycartoons.Thedopaminesystemalsorespondsrobustlytoaddictivedrugs,includingopiates,alcoholandcocaine.Thesedrugscanevokestrongeractivationthannaturalrewardsand,unlikenaturalrewards,theydonotcausesatiety.Astraightforwardinterpretationofthesefactsisthatthedopaminesystemisapleasurepathwayinthebrain.Thispotentiallyexplainswhyanimalsandpeoplewouldbewillingtopressbuttonsorpushleverstoactivatethedopamineneurons.Itmightalsoexplainwhysomedrugsaresoaddictive.Thestrongandprolongedactivationinducedbydrugscanactasa“super-reward"，makingdrugsevenmoredesirable.However,manymentaleventsoccurnearthetimeofareward,includingchangesinmotivation,arousal,attention,emotion,andlearning.Forexample,imaginepassingbyavendingmachinethatofferssweets.Ifyouaremotivatedbyhunger,yourattentionwillbedrawntothemachineandyouwillbecomemorealertasyouapproachit.Onceyouhaveeatenthesweets,youexperiencepleasure,yourbrainlearnstoassociatethevendingmachinewithreward,andyourhungerdecreases.Itislikelythatthedopaminesystemisinvolvedinmanyoftheseprocessesratherthanjustpleasureperse.Oneofthemostimportantaspectsofdopaminefunctionislearning.Researchersbelievethatdopamineneuronschangetheiractivitywhenexpectationsaboutrewarddonotmatchthereality,signallinga,rewardpredictionerror*thatdriveslearning.Forinstance,dopamineneuronsareactivatedbyunanticipatedrewards,buttheyaresuppressedwhenexpectedrewardsfailtomaterialise.Eventsfollowedbyincreasesindopamineactivationbecomeassociatedwithreward,andthosethatarefollowedbydecreasesarelinkedwithdisappointment.Iftheenvironmentisunchanging,allourbrainsneedtodotoobtainrewardistoengageinactionsthatactivatethedopamineneuronsandavoidtheonesthatsuppressthem.Itishighlyunlikelythatwehavemuchawarenessofthelearningthatdopamineactivationinduces,suchasmakingusattachedtothingsweunknowinglyassociatewithdopamineactivation.Thislackofawarenessmightexplainwhypeopleoftenmakeseeminglyirrationalormaladaptivechoices.Imagineadrugaddicttakingcocaine.Becausethepleasurefromcocainedoesnotsatiatelikeanaturalreward,thedopamineactivation,andhencedrug-inducedlearning,occurswitheachpuffofthecrackpipe,makingtheactualpipeanobjectwhichtheaddictisdrawnto.Canbrainresearchbeusedtoovercometheeffectsofdopamineinaddiction?Neuroscientistsareactivelypursuingthecreationofdrugsthatblockthelearninginducedbydopamineinaddiction.However,theyhavehadlimitedsuccess,foritisdifficulttocreateadrugthatblocksthelearningwithoutalsoblockingotherfunctionsofdopamine,suchasfeelingalert,motivatedandhappy.Dopamine-inducedlearningiscertainlynotthewholestorybehindaddiction,butitdoessuggestthatweshouldconsiderwhetheraddictionissomethingthathumanreasoningonitsowncanovercome.Thesamemightverywellalsoapplytoothereverydayfailuresofwillpower,suchasovereating.Ourspecialcerebralcortexmaybeincontrolofouractions,butourprimitivedopaminesystemmayverywellserveasitsteacher.Source:http:Questions1-10Dothefollowingstatementsagreewiththeclaimsofthewriterinthepassage?YesifthestatementagreeswiththeclaimsofthewriterNoifthestatementcontradictstheclaimsofthewriterNotGivenifitisimpossibletosaywhatthewriterthinksaboutthis1. Therearemanywaysinwhichhumanbrainsdifferfromthebrainsofotheranimals.2. Thecellsinthebrainthatmakeuseofdopamineasameansofcommunicationareuniquetohumans.3. Dopaminecanbecharacterisedinotherwaysthanassimplyachemicalinvolvedinthesensationofpleasure.4. Theexperimentcarriedoutonahumansubjectin1970wasunethicalbecausei