Itisfairlyclearthatsleepingperiodmusthavesomefunction，andbecausethereissomuchofitthefunctionwouldseemtoeimportant.Speculationsaboutisnaturehavebeengoingonforliterallythousandsofyears，andoneoddfindingthatmakestheproblempuzzlingisthatitlooksverymuchasifsleepingisnotsimplyamatterofgivingthebodyarest.'Rest'，intermsofmusclerelaxationandsoon，canbeachievedbyabriefperiodlying，orevensittingdown.Thebody'stissuesareself-repairingandself-restoringtoadegree，andfunctionbestwhenmoreorlesscontinuouslyactive.Infactabasicamountofmovementoccursduringsleepwhichisspecificallyconcernedwithpreventingmuscleinactivity.
Ifitisnotaquestionofrestingthebody，thenperhapsitisthebrainthatneedsresting？Thismightbeaplausiblehypothesiswereitnotfortwofactors.Firsttheelectroencephalograph（whichissimplyadeviceforrecordingtheelectricalactivityofthebrainbyattachingelectrodestothescalp）showsthatwhilethereisachangeinthepatternofactivityduringsleep，thereisnoevidencethatthetotalamountofactivityisanyless.Thesecondfactorismoreinterestingandmorefundamental.SomeyearsagoanAmericanpsychiatristnamedWilliamDementpublishedexperimentsdealingwiththerecordingofeye-movementsduringsleep.Heshowedthattheaverageindividual'ssleepcycleispunctuatedwithpeculiarburstsofeye-movements，somedriftingandslow，othersjerkyandrapid.Peoplewokenduringtheseperiodsofeye-movementsgenerallyreportedthattheyhadbeendreaming.Whenwokenatothertimestheyreportednodreams.Ifonegroupofpeopleweredisturbedfromtheireye-movementsleepforseveralnightsonend，andanothergroupweredisturbedforanequalperiodoftimebutwhentheywerenoexhibitingeye-movements，thefirstgroupbegantoshowsomepersonalitydisorderswhiletheothersseemedmoreorlessunaffected.Theimplicationsofallthiswerethatitwasnotthedisturbanceofsleepthatmattered，butthedisturbanceofdreaming.
speculationn.推测
literallyadv.确实
oddadj.奇特的
tissuen.组织
plausibleadj.似乎有理的
hypothesisn.假说
electroencephalographn.脑电图仪
electroden.电极
scalpn.头皮
psychiatristn.精神病学家
punctuatev.不时介入
jerkyadj.急动的
disordern.失调
implicationn.表明
很清楚，睡眠必然具有某种作用。睡眠占去那么多时间，所以其作用似乎还是很重要。人们对睡眠作用的种种猜测，确实有数千年之久。一项使人对这个问题感到困惑的奇怪的发现是，睡眠在很大程度似乎并不仅仅是为了使身体得到休息。"休息"，从使肌肉得到放松等方面来看，只要稍微躺一躺，甚至坐一坐就能达到。人体组织在一定程度上有自我修补和自我恢复的能力，有张有弛地连续活动时，其功能最佳。事实上，睡眠状态下仍有着基本的活动量，以防止肌肉活动停止。
如果睡眠的功能不是在于使身体得到休息，那么也许是让大脑得以休息？若不是下面两点，这种假使似乎是有道理的。第一点，脑电图记录仪（不过是一种把电极接到头皮上记录脑电活动的仪器）显示，人在睡眠时大脑活动的方式有变化，但没有迹象表明，其活动总量有任何减少。第二点更有意思，也更重要。前些年，美国一位精神病学者发表了一篇报告，报告中记录了眼球在睡眠时的活动情况。他指出，平常人的睡眠周期中不时伴有一阵阵奇怪的眼球队活动，这些活动有的飘忽而缓慢，有的急剧而快速。在眼球活动期间被叫醒的人都说自己在做梦；在其他期间叫醒他们，则说没有做梦。如果有两组人，一组人连续几夜在眼球队活动时被叫醒；另一组人也是连续几夜被叫醒，但是在眼球队没活动时被叫醒的。结果，第一组人开始出现性格失常，而第二组人似乎没受什么影响。这一切暗示我们：睡眠受到干忧没关系，而做梦受到干忧是有问题的。