译文why-we-sleep-a-biological-perspective

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Reading3WhyWeSleep:ABiologicalPerspective从生物学角度考察人类为什么要睡眠ByJeromeM.SiegelSection11Birdsdoit,beesdoit,andevenfruitfliesappeartodoit.Humanscertainlydoit.Thesubjectisnotlove,butsleep.Shakespeare'sMacbethsaidit“knitsuptheraveledsleeveofcare”andwasthe"balmofhurtminds,greatnature'ssecondcourse,chiefnourisherinlife'sfeast."Cervantes'sSanchoPanzasangitspraisesas"thefoodthatcuresallhunger,thewaterthatquenchesallthirst,thefirethatwarmsthecold,thecoldthatcoolstheheart...thebalancingweightthatlevelstheshepherdwiththeking,andthesimplewiththewise."鸟儿/蜜蜂儿/甚至是苍蝇儿都需要睡觉,人类当然也需要睡觉.本主题所谈论的非爱情,而是睡眠.莎士比亚说,那是”织补关照的袖口”和那是”心灵慰藉,自然的赋予,生命的滋养”科文特斯.伯查却赞歌”食足肚饿,水慰口渴,火暧冬寒,寒静热血......这均衡的赐予抚平了牧人与国王的差别,抚平了愚者与智者的差别.”2Thesimpleandthewisehavelongcontemplatedtworelatedquestions:Whatissleep,andwhydoweneedit?Anobviousanswertothelatteristhatadequatesleepisnecessarytostayalertandawake.Thatresponse,however,dodgestheissueandistheequivalentofsayingthatyoueattokeepfrombeinghungryorbreathetowardofffeelingsofsuffocation.Therealfunctionofeatingistosupplynutrients,andthefunctionofbreathingistotakeinoxygenandexpelcarbondioxide.Butwehavenocomparablystraightforwardexplanationforsleep.Thatsaid,sleepresearch---lessthanacenturyoldasafocusedfieldofscientificinquiry---hasgeneratedenoughinsightforinvestigatorstoatleastmakereasonableproposalsaboutthefunctionofthesomnolentstatethatconsumesonethirdofourlives.人们长期关注着两个相关的问题:什么是睡眠,为什么要睡眠?一个最新的答案是:睡眠是为了保持警觉和清醒的需要.然后,这个答案回避了问题本身,如同说吃饭是为了充饥,呼吸是为了免除窒息一样.其实,吃饭的作用是提供营养,呼吸的作用是吸入氧气和呼出二氧化碳.但我们没有同样地直接回答睡眠是为了什么.也就是说,人们对睡眠的研究,在不到一个世纪以来将之作为一个重要的研究领域已经进行了充分的探究,至少对于这一占去人生三分之一的睡眠的功能提出了合理的解释.Section2Whatissleep?3Despitethedifficultyinstrictlydefiningsleep,anobservercanusuallytellwhenasubjectissleeping:thesleeperordinarilyexhibitsrelativeinattentiontotheenvironmentandisusuallyimmobile.(Dolphinsandothermarinemammalsswimwhilesleeping,however,andsomebirdsmaysleepthroughlongmigrations.)尽管严格定义睡眠是困难的.但是观测者一般能看出什么时候是进入睡眠状态:睡眠者通常对环境失去注意,以及静止不动.4In1953sleepresearchpioneerNathanielKleitmanandhisstudentEugeneAserinskyoftheUniversityofChicagodecisivelyoverthrewthecommonlyheldbeliefthatsleepwassimplyacessationofmostbrainactivity.Theydiscoveredthatsleepwasmarkedbyperiodsofrapideyemovement,commonlynowknownasREMsleep.Anditsexistenceimpliedthatsomethingactiveoccurredduringsleep.AllterrestrialmammalshavebeenexaminedexhibitREMsleep,which9 alternateswithnon-REMsleep,alsocalledquietsleep,inaregularcycle.睡眠研究的先行者芝加哥大学的纳撒尼尔与他的学生尢金在1953年果断地推翻以往认为睡眠是大部分大脑活动的简单停止的观点.他们发现睡眠是以快速动眼期开始的活动,现在通常称作快速动眼期睡眠.这一时期的存在意味着,当睡眠发生时,某一活动开始出现.所有的陆生哺乳动物经检都呈现出这一时期,它与一种叫做静睡眠的非快速动眼期轮换出现,并有规律地循环.5Morerecently,thefieldhasmadeitsgreatestprogressincharacterizingthenatureofsleepatthelevelofnervecells(neurons)inthebrain.Inthepast20years,scientistshavemasteredtechniquesforguidingfinemicrowiresintovariousbrainregions.Suchwiresproducenopainonceimplantedandhavebeenusedinhumansaswellasinawiderangeoflaboratoryanimalswhiletheywentabouttheirnormalactivities,includingsleep.Thesestudiesshowed,asmightbeexpected,thatmostbrainneuronsareatorneartheirmaximumlevelsofactivitywhilethesubjectisawake.Butneuronaldoingsduringsleeparesurprisinglyvariable.DespitethesimilarpostureandinattentiontotheenvironmentthatasleepershowsduringbothREMandnon-REMsleep,thebrainbehavescompletelydifferentlyinthetwostates.最近更多在大脑神经细胞水平上描述睡眠特性的领域取得了巨大的进展.过去20年,科学家已经掌握了控制精细微电极导入脑部神经各区域的技术.这种电极植入是无痛的,它已经使用在人类上,也广泛地使用在实验动物上,并不影响他们包括睡眠在内的一切正常活动.这些研究结果正如我们所预料的那样,当研究对象清醒的时候,其大部分脑神经在或接近最大的活跃状态.但是当睡眠时神经元的表现却惊人地不同.尽管睡眠者在快速动眼期和非快速动眼期睡眠的姿势和不注意的条件相同,脑神经在两种睡眠状态中的活动却完全不同.6Duringnon-REMsleep,cellsindifferentbrainregionsdoverydifferentthings.Mostneuronsinthebrainstem,immediatelyabovethespinalcord,reduceorstopfiring,whereasmostneuronsinthecerebralcortexandadjacentforebrainregionsreducetheiractivitybyonlyasmallamount.Whatchangesmostdramaticallyistheiroverallpatternofactivity.Duringtheawakestate,aneuronmoreorlessgoesaboutitsownindividualbusiness.Duringnon-REMsleep,incontrast,adjacentcorticalneuronsfiresynchronously,witharelativelylowfrequencyrhythm.(Seeminglyparadoxically,thissynchronouselectricalactivitygenerateshigher-voltagebrainwavesthanwakingdoes.Yetjustasinanidlingautomobile,lessenergyisconsumedwhenthebrain"idles"inthisway.)Breathingandheartratetendtobequiteregularduringnon-REMsleep,andreportsofvividdreamsduringthisstatearerare.在非快速动眼期中,不同区域的脑神经细胞做不同的事情.在脊髓上面的大部分脑干细胞减少或停止活动,然而,大脑皮层和邻近的前脑区稍稍减少活动.最大的变化是整个大脑的活动形式.在清醒状态,每一个神经细胞或多或少地从事着自己的事情.在非快速动眼期却形成对比,邻近的皮层细胞以一种相对低频的节奏同步地活动.(看起来似乎自相矛盾,这种同步电活动产生比清醒时还要高压的脑电波.然而,正如空转的机器,用这种方式消耗很少的能量.)在非快速动眼期时,呼吸和心率趋于平静和有规律,此阶段,罕有梦境报道.7Averysmallgroupofbraincells(perhapstotalingjust100,000inhumans)atthebaseoftheforebrainismaximallyactiveonlyduringnon-REMsleep.Thesecellshavebeencalledsleep-onneuronsandappeartoberesponsibleforinducingsleep.Theprecisesignalsthatactivatethesleep-onneuronsarenotyetcompletelyunderstood,butincreasedbodyheatwhileanindividualisawakeclearlyactivatessomeofthesecells,whichmayexplainthedrowsinessthatsooftenaccompaniesahotbathorasummerdayatthebeach.在脑前区的基部有一小撮9 的脑细胞（大概总量为100000个）仅在非快速动眼期表现最活跃.这些细胞好像行使管理包括睡眠在内的职责,它们被称为睡眠性神经细胞.激发睡眠性神经细胞的精确信号目前仍然不完全了解,但是当个体清醒/体温升高时部分这些睡眠性神经细胞是明显地被激活,这种现象可以用来解释热水澡或夏日海滨浴后的睡意.8Ontheotherhand,brainactivityduringREMsleepresemblesthatduringwaking.Brainwavesremainatlowvoltage,becauseneuronsarebehavingindividually.Andmostbraincellsinboththeforebrainandbrainstemregionsarequiteactive,signalingothernervecellsatratesashighas---orhigherthan---ratesseeninthewakingstate.Thebrain'soverallconsumptionofenergyduringREMsleepisalsoashighaswhileawake.ThegreatestneuronalactivityaccompaniesthefamiliartwitchesandeyemotionthatgiveREMsleepitsname.Specializedcellslocatedinthebrainstem,calledREMsleeponcells,becomeespeciallyactiveduringREMsleepand,infactappeartoberesponsibleforgeneratingthisstate.另一方面,快速动眼期的脑活动与清醒时的脑活动相似.脑电波仍然处于低电压状态,脑细胞仍然在各司其职.同时,脑前区和脑干区大部分细胞仍然十分活跃,发出信号给其它神经细胞在比率上等于或高于清醒状态.在快速动眼期整个大脑的能量消耗也与清醒状态一样.在这个被称为快速动眼期的时段里,熟悉的抽搐和眼动伴随着最强烈的神经活动发生.9OurmostvividdreamsoccurduringREMsleep,anddreamingisaccompaniedbyfrequentactivationofthebrain'smotorsystems,whichotherwiseoperateonlyduringwakingmovement.Fortunately,mostmovementduringREMsleepisinhibitedbytwocomplementarybiochemicalactionsinvolvingneurotransmitters,thechemicalsthatphysicallycarrysignalsfromoneneurontoanotheratthesynapse(thecontactpointbetweentwoneurons).Thebrainstopsreleasingneurotransmittersthatwouldotherwiseactivatemotoneurons,anditdispatchesotherneurotransmittersthatactivelyshutdownthosemotoneurons.Thesemechanisms,however,donotaffectthemotoneuronsthatcontrolthemusclesthatmovetheeyes,allowingtherapideyemovementsthatgivetheREMsleepstageitsname.我们的梦境出现在快速动眼期,梦境是随着大脑动力系统的频繁激活而产生的,大脑动力系统除在快速动眼期运转外,仅见于清醒状态.幸运的是,在快速动眼期很多运动都被两种互补的生化活动抑制住,这生化活动涉及神经传导物质,也就是一种在物理上能将信息在神经突触(就是联系两个神经细胞之间的节点)之间进行运载的化学物质.大脑停止释放神经传导物质,否则将激活运动神经元,和分配其它的神经传导物质及时地阻断那些运动神经元.然而,这种机制并不影响控制眼动的运动神经元的活动.10REMsleepalsoprofoundlyaffectsbrainsystemsthatcontrolthebody'sinternalorgans.Forexample,heartrateandbreathingbecomeirregularduringREMsleep,justastheyareduringactivewaking.Also,bodytemperaturebecomeslessfinelyregulatedanddrifts,likethatofareptile,towardtheenvironmentaltemperature.快速动眼期也对大脑系统控制人体内脏器官产生深刻的影响.例如,在快速动眼期心率和呼吸如清醒时一样,变得不规律.体温也变得漂忽不稳定,像爬行动物一样趋向于环境的温度.11Thisbriefdescriptionofsleepattheneuronallevelsisbothaccurateandasunsatisfyingasbeingawakenedbeforethecompletionofagoodnight'sslumber.Thetantalizingquestionpersists:Whatissleepfor?以上从神经元的水平对睡眠所进行的简述是精确的,但却是无法令人满意的,不满意之处在于,它如同没有完全睡够就被叫醒的那种感觉.那个撩人的问题还在:为什么要睡眠?Section3TheFunctionofSleep9 12Atarecentsleepconference,anattendeecommentedthatthefunctionofsleepremainsamystery.Thechairofthesessionarguedvehementlyagainstthatposition---shedidnot,however,provideaconcretedescriptionofexactlywhysleep'sfunctionwasnolongermysterious.Butbasedonthecurrentlyavailableevidence,Icanputforthwhatmanyofusfeelaresomereasonablehypotheses.在最近的一个关于睡眠的研讨会上，一个参会者发表评论说睡眠的功能仍是个秘密。而这个会议的主席却持相反意见，并准确的提出了为什么睡眠的功能不再是秘密的描述。但是基于目前可靠的证据，我提出一些大多数人认为是合理的假设。13Oneapproachtoinvestigatingthefunctionofsleepistoseewhatphysiologicalandbehavioralchangesresultfromalackofit.Morethanadecadeagoitwasfoundthattotalsleepdeprivationinratsleadstodeath.Theseanimalsshowweightlossdespitegreatlyincreasedfoodconsumption,suggestingexcessiveheatloss.Theanimalsdie,forreasonsyettobeexplained,within10to20days,fasterthaniftheyweretotallydeprivedoffoodbutsleptnormally.一个研究睡眠功能的方法是，看不睡眠的情况下生理和行为有什么变化。十多年前实验发现，如果没有睡眠，小鼠会死亡。这些被实验的动物表现出即使增加食物，体重减轻，并提示，过量的热散失。不睡眠，在10-20天动物会死，比不给食物但可睡眠的情况下死得更快，这死因仍待解释。14Inhumans,averyraredegenerativebraindiseasecalledfatalfamilialInsomnialeadstodeathafterseveralmonths.Whetherthesleeplossitselfisfatalorotheraspectsofthebraindamagearetoblameisnotclear.Sleepdeprivationstudiesinhumanshavefoundthatsleepinessincreaseswithevensmallreductionsinnightlysleeptimes.Beingsleepywhiledrivingorduringotheractivitiesthatrequirecontinuousvigilanceisasdangerousasconsumingalcoholpriortothosetasks.Butexistingevidenceindicatesthat"helping"peopletoincreasesleeptimewithlong-termuseofsleepingpillsproducesnoclear-cuthealthbenefitandmayactuallyshortenlifespan.(Aboutsevenreportedhoursofsleepanightcorrelateswithlongerlifespansinhumans.)Soinexorableisthedrivetosleepthatachievingtotalsleepdeprivationrequiresrepeatedandintensestimulation.Researchersemployingsleepdeprivationtostudysleeparethereforequicklyconfrontedwiththedifficultyofdistinguishingtheeffectsofstressfromthoseofsleeploss.Researchersalsostudythenaturalsleephabitsofavarietyoforganisms.Animportantclueaboutthefunctionofsleepisthehugevariationintheamountthatdifferentspeciesneed.Forexample,theopossumsleepsfor18hoursaday,whereastheelephantgetsbywithonlythreeorfour.Closelyrelatedspeciesthathavegenetic,physiologicalandbehavioralsimilaritiesmightalsobeexpectedtohavesimilarsleephabits.Yetstudiesoflaboratory,zooandwildanimalshaverevealedthatsleeptimesareunrelatedtotheanimals'taxonomicclassification:therangeofsleeptimesofdifferentprimatesextensivelyoverlapsthatofrodents,whichoverlapsthatofcarnivores.andsoonacrossmanyordersofmammals.Ifevolutionaryrelatednessdoesnotdeterminesleeptime,thenwhatdoes?在人类中，极少有致命性家族性失眠症的脑疾病发生.睡眠缺失本身是否致命的或其他方面的脑损伤是罪魁祸首还不清楚。有关人类剥夺睡眠的研究发现,只需要减少很少的晚睡时间就可以使睡意增加.在困倦状态下驾车或做一些需要保持警醒的事情,那是如同酒后接受这些任务一样地危险.但现存的证据表明,用一些安眠的药物去帮助人们延长睡眠时间,没有明确的健康益处,事实上可能缩短寿命.(报道说,约每晚上7个小时的睡眠与长寿有关.)如此不可阻挡的睡眠内驱力使得取得实验所需的无眠总量需要反复地做和需要给予很强的激励.因而,研究者雇用无眠去研究睡眠很快就面临区分是压力效应还是睡眠缺失的困难.9 研究人员也研究各种生物体的自然睡眠习惯.关于睡眠功能的一个重要线索是不同生物种类需求不同,存在巨大的变数.例如，负鼠要睡每天18小时，而大象只需要3-4小时.近缘种的遗传、生理和行为相似性可能也会有类似的睡眠习惯.然而,实验室动物园野外的动物研究揭示了睡眠时间与动物的分类学分类无关.不同灵长目动物的睡眠时间幅度与啮齿目的大量重叠,啮齿目的睡眠时间又大量与肉食性动物等等,睡眠时间的重叠交错在哺乳动物中普通存在.15Theextraordinaryansweristhatsizeisthemajordeterminant:biggeranimalssimplyneedlesssleep.Elephants,giraffesandlargeprimates(suchashumans)requirerelativelylittlesleep;rats,cats,volesandothersmallanimalsspendmostoftheirtimesleeping.Thereasonisapparentlyrelatedtothefactthatsmallanimalshavehighermetabolicratesandhigherbrainandbodytemperaturesthanlargeanimalsdo,andmetabolismisamessybusinessthatgeneratesfreeradicals---extremelyreactivechemicalsthatdamageandevenkillcells.Highmetabolicratesthusleadtoincreasedinjurytocellsandthenucleicacids,proteinsandfatswithinthem.惊人的答案是,大小是睡眠长短主要的决定因素:大的动物仅需少许的睡眠,如大象长颈鹿大的灵长目动物(如人)需要相对少的睡眠;老鼠猫田鼠和其它小个体动物需要很多的睡眠时间.这原因显然与小个体动物比大个体动物有较高的代谢速率和较高的脑温及体温有关,新陈代谢是个复杂的机能,它能产生损害甚至杀死体内细胞,引起极端反应的化学物质—自由基.因此,高的代谢速率就会加大对体内细胞和核酸蛋白质脂肪的损害.16Free-radicaldamageinmanybodytissuescanbedealtwithbyreplacingcompromisedcellswithnewones,producedbycelldivision:however,mostbrainregionsdonotproducesignificantnumbersofnewbraincellsafterbirth.Thelowermetabolicrateandbraintemperatureoccurringduringnon-REMsleepseemtoprovideanopportunitytodealwiththedamagedoneduringwaking.Forexample,enzymesmaymoreefficientlyrepaircellsduringperiodsofinactivity.Oroldenzymes,themselvesalteredbyfreeradicals,maybereplacedbynewlysynthesizedonesthatarestructurallysound.自由基损害的身体组织可以通过产生新细胞的方式来补偿,新细胞的产生需要细胞分裂,然而,大脑大部分区域在出生后不能再产生有效数量的新脑细胞.低速率的代谢和低脑温在非快速动眼期出现看来是提供应对清醒状态下损害的一种条件.例如,酶在休眠状态可以高效修复受损细胞.或者老酶自己被自由基改变,被结构完整的新合成的酶取代.17LastyearmygroupattheUniversityofCaliforniaatLosAngelesobservedwhatwebelievetobethefirstevidenceforbraincelldamageinrats,occurringasadirectresultofsleepdeprivation.Thisfindingsupportstheideathatnon-REMsleepwardsoffmetabolicharm.去年我的研究小组在旧金山加利佛尼严大学首次在小鼠中观察到由睡眠缺失引起的大脑细胞受损的证据.这一发现支持了非快速动眼期是避开代射损害的观点.18REMsleep,however,istheproverbialriddlewrappedinamysteryinsideanenigma.Thecell-repairhypothesiscouldexplainnon-REMsleep,butitfailstoaccountforREMsleep.Afterall,downtimerepaircannotbetakingplaceinmostbraincellsduringREMsleep,whenthesecellsareatleastasactiveasduringwaking.ButaspecificgroupofbraincellsthatgoesagainstthistrendisofspecialinterestinthesearchforapurposeofREMsleep.众所周知,快速动眼期是一个被包裹在神秘秘团之中的秘语.细胞修复假说能对非快速动眼期进行解释,但却不能对快速动眼期进行解释.毕竟,当大脑大部分细胞处在相当于清醒时最低活跃程度的快速动眼期时,停机修复是不可能发生的.但是,一群与不同于这种趋势的特殊细胞成为研究快速动眼期功能的特别兴趣点.19RecallthatthereleaseofsomeneurotransmittersceasesduringREMsleep,therebydisablingbodymovementandreducingawarenessoftheenvironment.Thekeyneurotransmittersaffected9 aretermedmonoamines,becausetheyeachcontainachemicalentitycalledanaminegroup.Braincellsthatmakethesemonoaminesaremaximallyandcontinuouslyactiveinwaking.ButDennisMcGintyandRonaldHarperofD.C.L.A.discoveredin1973thatthesecellsstopdischargingcompletelyduringREMsleep.回想起在快速动眼期神经传导物质的释放终止,从而使身体运动和对周遭感觉失能.这关键起作用的神经传导物质叫做一元胺(因为它包含着一个叫做胺的化学基团).制造一元按的大脑细胞在清醒状态下是最大限度地和持续地活跃.可是,D.C.L.A的丹尼斯麦金蒂和罗纳德哈伯在1973年发现这些细胞在快速动眼期完全停止活动.20In1988MichaelRogawskioftheNationalInstitutesofHealthandIhypothesizedthatthecessationofneurotransmitterreleaseisvitalfortheproperfunctionoftheseneuronsandoftheirreceptors(themoleculesonrecipientcellsthatrelayneurotransmitters'signalsinthatcell).Variousstudiesindicatethatconstantreleaseofmonoaminescandesensitizetheneurotransmitters'receptors.TheinterruptionofmonoaminereleaseduringREMsleepthusmayallowthereceptorsystemsto"rest"andregainfullsensitivity.Andthisrestoredsensitivitymaybecrucialduringwakingformoodregulation,whichdependsontheefficientcollaborationofneurotransmittersandtheirreceptors.1988年国家卫生研究院的迈克尔.罗格斯奇和我假设,神经递质释放的终止是那些神经细胞及其受体(那些在受体细胞上传递神经递质信号的分子)极其重要的特有功能.多种研究表明,恒定地释放一元胺能使神经递质的受体失灵.在快速动眼期终止一元胺的释放因而可以允许受体系统”休息”,以致重获灵敏.恢复敏感性可能对清醒时的正常情绪是很重要的,它需要依靠神经递质及其受体的有效协调.Section4OtherPossibilities21WhatelsemightREMsleepdo?ResearcherssuchasFrederickSnyderandThomasWehroftheNationalInstitutesofHealthandRobertVertesofFloridaAtlanticuniversityhaveproposedthattheelevatedactivityduringREMsleepofbraincellsthatarenotinvolvedinmonoamineproductionenablesmammalstobemorepreparedthanreptilestocopewithdangeroussurroundings:Whenwakinginacoldenvironment,reptilesaresluggishandrequireanexternalheatsourcetobecomeactiveandresponsive.ButeventhoughmammalsdonotthermoregulateduringREMsleep,theintenseneuronalactivityduringthisphasecanraisebrainmetabolicrate,helpingmammalstomonitorandreactmorequicklytoagivensituationonwaking.TheobservationthathumansaremuchmorealertwhenawakenedduringREMsleepthanduringnon-REMperiodssupportsthisidea.快速动眼期还有别的功能？研究人员象弗雷德里格.斯尼特和国家卫生研究院的托马斯.威尔斯、佛罗里达大西洋大学的罗伯特.韦尔泰次曾提议大脑细胞在快速动眼期活力增强与一元胺物质无关,它是使哺乳动物较爬行动物能有更充分的准备去应付危险的环境:在寒冷的环境里,清醒着的爬行动物变得迟纯,需要外来的热源使自己变得活力和敏捷.即使哺乳动物在快速动眼期不调节体温,但在这一阶段紧张的神经活动能使大脑代谢率提高,以使哺乳动物在清醒时对既定的环境进行更快地监控和及时地反应.22Sleepdeprivationstudiesindicate,however,thatREMsleepmustdomorethanprimethebrainforwakingexperience.ThesestudiesshowthatanimalsmadetogowithoutREMsleepwillundergomorethantheusualamountwhentheyarefinallygiventheopportunity.Theyapparentlyseektomakeupthe"debt"---yetanothercluethatREMsleepisimportant.9 然而,剥夺睡眠的研究表明,快速动眼期所做事情一定比大脑基本清醒状态下所经历的事多.这些研究显示,动物如果没有快速动眼期那么将承受比最终获得睡眠时更多的付出.快速动眼期显然是为了寻求弥补”债务”,这一线索也是很重要的.23OldideasthatREMsleepdeprivationledtoinsanityhavebeenconvincinglydisproved(althoughstudiesshowthatdeprivingsomeoneofsleep,forexamplebyproddinghimorherawakerepeatedly,candefinitelycauseirritability).Infact,REMsleepdeprivationcanactuallyalleviateclinicaldepression.Themechanismforthisphenomenonisunclear.老的观点说在快速动眼期被剥夺时会导致神经错乱，这已经确证是错误的（尽管研究显示，剥夺了某人的睡眠，例如戳他或者反复叫醒他，这能肯定引起他的反感）.事实上,快速动眼期的剥夺实际上可以减轻临床忧郁症.这一现象的机制尚不清楚.24SomeresearchersarepursuingtheideathatREMsleepmighthavearoleinmemoryconsolidation,butasIexaminedindetailina2001articleinScience,theevidenceforthatfunctionisweakandcontradictory.ThefindingsthatargueagainstmemoryconsolidationincludethedemonstrationthatpeoplewhohavebraindamagethatpreventsREMsleep,orwhohaveadrug-inducedblockadeofREMsleep,havenormal--orevenimproved--memory.Andalthoughsleepdeprivationbeforeataskdisturbsconcentrationandperformance--sleepystudentsdonotlearnorthinkwell--REMdeprivationafteraperiodofalertlearningdoesnotappeartointerferewithretainingthenewinformation.Inaddition,dolphinsexperiencelittleornoREMsleepyetexhibitimpressivereasoningandlearningability.一些研究者认同这样一种观点:快速动眼期可能有巩固记忆的作用.但是,当我详细地查阅了2001年一篇在《科学》杂志上的文章后发现,提供论证这种功能的证据是微不足的和相矛盾的.这发现证明了阻止快速动眼期或因药物效应致快速动眼期缺失而损伤大脑的人,有正常甚至增强的记忆力,驳斥了巩固记忆的观点.尽管在给任务前的睡眠剥夺会打乱注意力和成效—-如昏昏欲睡的学生学习和思考都不好----但在一段警觉的学习之后再剥夺快速动眼期好像并不影响刚刚获得的信息的保持.此外,海豚很少甚至没有快速动眼期仍然展示令人钦佩的推理和学习能力.25Infact,learningabilityacrossspeciesdoesnotappeartoberelatedtototalREMsleepduration.HumansdonothaveparticularlylongREMsleeptimes--90to120minuteseachnight--comparedwithothermammals.(AndhumanswithhigherIQsorschoolperformancedonothavemore,orless,REMsleepthanthosewithlowerIQs.)TheamountoftimespentinREMdoeschangeoveranindividual'slife,however.Inallanimalsstudied,theportionofeachdaydevotedtoREMsleepishighestearlyinthesubject'slifeandfallsgraduallytoasteady,lowerlevelinadulthood,Anadditional,fascinatingfactemergesfromcomparingnumerousspecies:thebestpredictoroftheamountofREMsleeptimeforanadultinagivenspeciesishowimmaturetheoffspringofthatspeciesareatbirth.事实上,学习能力在物种间似乎与总的快速动眼期是无关的.与其它哺乳动物相比,人类没有特别长的快速动眼期,一般都是每晚上90-120分钟.(高IQ或高成绩的人比起IQ低的人来说,没有更多的甚至更少的快速动眼期.)然而,快速动眼期的时间花费量确能改变一个个体生活.在所在的研究动物中,早期对象其快速动眼期在一天的时间配额中是最高的,然后逐渐降低至保持平稳,低配额现象在成年期出现,另外,从大量的物种对比中产生了一个吸引人的事实:一个物种成体快速动眼期的时间量预测的最好预报器是该物种刚出生的后代.26In1999JackPettigrewandPaulMangeroftheUniversityofQueenslandinAustraliaandIwereabletostudyanunusualresearchsubject,theplatypus.ThisevolutionarilyearliestofextantmammalssurprisedusbyrevealingitselftobethechampionREMsleeper:abouteighthoursaday.Theplatypusisborncompletelydefenselessandblind,cannotthermoregulateorfindfoodon9 itsown,andstaysattachedtoitsmotherforweeksafterbirth.Attheotherextreme,thenewborndolphincanandmustthermoregulate,swim,followitsmotherandavoidpredators.Andadultdolphins,aspreviouslynoted,doalmostnoREMsleeping.1999年,我和澳大利亚昆特兰大学的杰特.贝蒂格鲁波尔.曼特有机会从事一项非寻常的项目研究:鸭嘴兽.进化上现存最古老的哺乳动物鸭嘴兽让我们惊奇于它是快速动眼期的冠军:大约8小时/天.鸭嘴兽的出生是随意的而且初生时是看不见的,不能自已调节体温,也不能自己找食物吃,粘附在母体身上达数周之久.在另一头,幼兽能且必须能调节体温/游泳/跟随母兽和避开敌害.成体兽,如前所述,几乎没有快速动眼期.27MichelJouvet,thepioneeringsleepresearcherwhodiscoveredfourdecadesagothatthebrainstemgeneratesREMsleep,hasaprovocativesuggestionforthelargeamountsofREMinimmatureanimals.REMsleep'sintenseneuronalactivityandenergyexpenditure,Jouvetbelieves,havearoleearlyinlifeinestablishingthegeneticallyprogrammedneuronalconnectionsthatmakeso-calledinstinctivebehaviorpossible.Beforebirth,orinanimalsthathavedelayedsensorydevelopment,REMsleepmayactasasubstitutefortheexternalstimulationthatpromptsneuronaldevelopmentincreaturesthatarematureatbirth.WorkbyHowardRoffwarg,directoroftheSleepDisordersCenterattheUniversityofMississippiMedicalCenter,andhiscolleaguessupportthisidea.RoffwargfoundthatpreventingREMsleepincatsduringthisearlyperiodcanleadtoabnormalitiesinthedevelopmentofthevisualsystem.四十年前发现脑干引发快速动眼期的睡眠研究先行者米切勒.纠威特,他对不成熟幼体动物花费大量时间于快速动眼期提出了一个大胆的建议.快速动眼期的强列的神经活动和能量消耗可能扮演着一个叫做先天性行为的角色,它在生命的早期建立起遗传神经连接的作用.在出生前,或动物的神经发育滞后,快速动眼期可以担当外部刺激的替代物,促进生物的神经发育,使之出生时是成熟的.在密西西比医学中心大学睡眠混乱中心工作的豪瓦尔德.罗弗瓦尔格主任和他的同事支持这一观点.罗弗瓦尔格发现在小鼠的早期发育中如果阻断它的快速动眼期,就会导致小鼠视觉神经系统发育畸形.28AnimalsthatengageinalotofREMsleepshortlyafterbirthcontinuetoexperiencerelativelylargeamountswhenmature.WhatisitaboutimmaturityatbirththatcausesREMsleepdurationtobehighlaterinlife?Insimpleevolutionaryterms,animalsthathavelowREMtimeshouldneedlessfuelandleavemoredescendantsthananimalsthatexperiencelongperiodsofhighenergyconsumption.Fromthatperspective,itismostlikelythatanimalsthatstillhavehighREMtimesmusthaveevolvedauseforREMsleepthatisnotfoundinprecocialanimals.Butthatfunctionremainstobeidentified.SleepresearchersareconfidentthatprogressinidentifyingthebrainregionsthatcontrolREMandnon-REMsleepwillsoonleadtoamorecomprehensiveandsatisfyingunderstandingofsleepanditsfunctions.Aswefurtherstudythemechanismsandevolutionofsleep,wewillprobablygaininsightsintoexactlywhatisrepairedandrested,whytheseprocessesarebestdoneinsleep,andwhyknittingupShakespeare'sraveledsleeveofcareultimatelyhelpsustostayawake.动物在出生后很快需要大量的快速动眼期,直到经历当个体成熟时相对较大量的过程.究竟是刚出生幼体的什么引起生命后期需要大量的快速动眼期?在简单的进化关系里,少量快速动眼期的动物比长期高能量消耗的动物需要较少的能量和生下更多的后代.从这一角度来看,那些还在大量快速动眼期的动物最有可能必须进化到没有快速动眼期作用的早熟性动物.但这种进化活动仍需有待确定.睡眠研究者确信,控制快速动眼期和非快速动眼期的大脑区域识别研究进展将很快引来对睡眠及其功能的全面和满意的认识.当我们深入地研究睡眠的机制和进化时,我们可能会9 对什么是修复,什么是休息,为什么修复和休息最好是在睡眠中进行,为什么织补莎士比亚短缺的袖子有一个深刻的理解,最终帮助我们保持清醒.9