科普

　　标题：Howthebraincontrolssleep
　　作者：MASSACHUSETTSINSTITUTEOFTECHNOLOGY
　　原文链接：http：www。eurekalert。orgpubreleases201510miothtb101315。php
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　　CAMBRIDGE，MASleepisusuallyconsideredanallornothingstate：Thebrainiseitherentirelyawakeorentirelyasleep。However，MITneuroscientistshavediscoveredabraincircuitthatcantriggersmallregionsofthebraintofallasleeporbecomelessalert，whiletherestofthebrainremainsawake。
　　Thiscircuitoriginatesinabrainstructureknownasthethalamicreticularnucleus（TRN），whichrelayssignalstothethalamusandthenthebrainscortex，inducingpocketsoftheslow，oscillatingbrainwavescharacteristicofdeepsleep。Slowoscillationsalsooccurduringcomaandgeneralanesthesia，andareassociatedwithdecreasedarousal。WithenoughTRNactivity，thesewavescantakeovertheentirebrain。
　　TheresearchersbelievetheTRNmayhelpthebrainconsolidatenewmemoriesbycoordinatingslowwavesbetweendifferentpartsofthebrain，allowingthemtoshareinformationmoreeasily。
　　Duringsleep，maybespecificbrainregionshaveslowwavesatthesametimebecausetheyneedtoexchangeinformationwitheachother，whereasotheronesdont，saysLauraLewis，aresearchaffiliateinMITsDepartmentofBrainandCognitiveSciencesandoneoftheleadauthorsofthenewstudy，whichappearstodayinthejournaleLife。
　　TheTRNmayalsoberesponsibleforwhathappensinthebrainwhensleepdeprivedpeopleexperiencebriefsensationsofzoningoutwhilestrugglingtostayawake，theresearcherssay。
　　ThepapersotherfirstauthorisJakobVoigts，anMITgraduatestudentinbrainandcognitivesciences。SeniorauthorsareEmeryBrown，theEdwardHoodTaplinProfessorofMedicalEngineeringandComputationalNeuroscienceatMITandananesthesiologistatMassachusettsGeneralHospital，andMichaelHalassa，anassistantprofessoratNewYorkUniversity。OtherauthorsareMITresearchaffiliateFranciscoFloresandMatthewWilson，theShermanFairchildProfessorinNeurobiologyandamemberofMITsPicowerInstituteforLearningandMemory。
　　Localcontrol
　　Untilnow，mostsleepresearchhasfocusedonglobalcontrolofsleep，whichoccurswhentheentirebrainisawashinslowwavesoscillationsofbrainactivitycreatedwhensetsofneuronsaresilencedforbriefperiods。
　　However，recentstudieshaveshownthatsleepdeprivedanimalscanexhibitslowwavesinpartsoftheirbrainwhiletheyarestillawake，suggestingthatthebraincanalsocontrolalertnessatalocallevel。
　　TheMITteambeganitsinvestigationoflocalcontrolofalertnessordrowsinesswiththeTRNbecauseitsphysicallocationmakesitperfectlypositionedtoplayaroleinsleep，Lewissays。TheTRNsurroundsthethalamuslikeashellandcanactasagatekeeperforsensoryinformationenteringthethalamus，whichthensendsinformationtothecortexforfurtherprocessing。
　　Usingoptogenetics，atechniquethatallowsscientiststostimulateorsilenceneuronswithlight，theresearchersfoundthatiftheyweaklystimulatedtheTRNinawakemice，slowwavesappearedinasmallpartofthecortex。Withmorestimulation，theentirecortexshowedslowwaves。
　　Wealsofoundthatwhenyouinducetheseslowwavesacrossthecortex，animalsstarttobehaviorallyactliketheyredrowsy。Theyllstopmovingaround，theirmuscletonewillgodown，Lewissays。
　　TheresearchersbelievetheTRNfinetunesthebrainscontroloverlocalbrainregions，enhancingorreducingslowwavesincertainregionssothoseareascancommunicatewitheachother，orinducingsomeareastobecomelessalertwhenthebrainisverydrowsy。Thismayexplainwhathappensinhumanswhentheyaresleepdeprivedandmomentarilyzoneoutwithoutreallyfallingasleep。
　　Iminclinedtothinkthathappensbecausethebrainbeginstotransitionintosleep，andsomelocalbrainregionsbecomedrowsyevenifyouforceyourselftostayawake，Lewissays。
　　Naturalsleepandgeneralanesthesia
　　Understandinghowthebraincontrolsarousalcouldhelpresearchersdesignnewsleepandanestheticdrugsthatcreateastatemoresimilartonaturalsleep。StimulatingtheTRNcaninducedeep，nonREMlikesleepstates，andpreviousresearchbyBrownandcolleaguesuncoveredacircuitthatturnsonREMsleep。
　　Brownadds，TheTRNisrichinsynapsesconnectionsinthebrainthatreleasetheinhibitoryneurotransmitterGABA。Therefore，theTRNisalmostcertainlyasiteofactionofmanyanestheticdrugs，giventhatalargeclassesofthemactatthesesynapsesandproduceslowwavesasoneoftheircharacteristicfeatures。
　　PreviousworkbyLewisandcolleagueshasshownthatunliketheslowwavesofsleep，theslowwavesundergeneralanesthesiaarenotcoordinated，suggestingamechanismforwhythesedrugsimpairinformationexchangeinthebrainandproduceunconsciousness。