2024剑桥雅思讲义Yes_No_NG_Questions_Strategy_Practice.docx
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1、Whatisdopamine-andisittoblameforouraddictions?Thekeydifferencebetweenhumanbrainsandthoseofotheranimalsisthesizeandcomplexityofourcerebralcortex,thebrainsouterlayerofneuraltissue.Wethereforetendtofocusourattentiononthisarea,believingthatouruniquementallifeisduetothismasterpieceofevolution.However,weo
2、ftenignorethebitsthatarenearlyidenticalbetweenhumansandanimals,suchasthetinygroupofbraincellsthatusethechemicaldopaminetocommunicatewithotherbraincells.Dopamineisoftendescribedasthebrain,spleasurechemica,butitisactuallyinvolvedinalargenumberofphysicalandmentalprocesses.Itisusedbyaclusterofneuronsint
3、hemidbraintotransmitmessagestootherneurons.Thedopamineneuronsaresmallinnumber(0.0006%oftheneuronsinthehumanbrain)andtheyareobservedinallmammalsandevenusimpleanimalssuchasturtles.Inthe1950s,researchersdiscoveredthatratsappearedtoenjoythestimulationofthenervebundlethatlinksthedopamineneuronswiththeirt
4、argetsintheforebrain.Theratswouldlearntopressaleverforthiskindofstimulation,and,leftunchecked,woulddosothousandsoftimesinaday.Asimilar(andwhollyunethical)experimentwasperformedin1970onahumanpatient.Liketherats,thepatientlearnedtopressabuttontostimulatethedopaminenervebundle,pressingthebuttonupto1500
5、timesoverthecourseofathree-hoursessionandreportingfeelingsofpleasureduringthestimulation.Sincethen,studieshaveshownthatthedopaminesystemcanbeactivatedbyawiderangeofpleasantexperiences,suchaseating,sexualintercourse,gettingrevenge,winningvideogames,listeningtomusic,earningmoneyandreadingfunnycartoons
6、.Thedopaminesystemalsorespondsrobustlytoaddictivedrugs,includingopiates,alcoholandcocaine.Thesedrugscanevokestrongeractivationthannaturalrewardsand,unlikenaturalrewards,theydonotcausesatiety.Astraightforwardinterpretationofthesefactsisthatthedopaminesystemisapleasurepathwayinthebrain.Thispotentially
7、explainswhyanimalsandpeoplewouldbewillingtopressbuttonsorpushleverstoactivatethedopamineneurons.Itmightalsoexplainwhysomedrugsaresoaddictive.Thestrongandprolongedactivationinducedbydrugscanactasa“super-reward,makingdrugsevenmoredesirable.However,manymentaleventsoccurnearthetimeofareward,includingcha
8、ngesinmotivation,arousal,attention,emotion,andlearning.Forexample,imaginepassingbyavendingmachinethatofferssweets.Ifyouaremotivatedbyhunger,yourattentionwillbedrawntothemachineandyouwillbecomemorealertasyouapproachit.Onceyouhaveeatenthesweets,youexperiencepleasure,yourbrainlearnstoassociatethevendin
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