It is fairly clear that sleeping period must have some function， and because there is so much of it the function would seem to e important. Speculations about is nature have been going on for literally thousands of years， and one odd finding that makes the problem puzzling is that it looks very much as if sleeping is not simply a matter of giving the body a rest. 'Rest'， in terms of muscle relaxation and so on， can be achieved by a brief period lying， or even sitting down. The body's tissues are self-repairing and self-restoring to a degree， and function best when more or less continuously active. In fact a basic amount of movement occurs during sleep which is specifically concerned with preventing muscle inactivity.

    If it is not a question of resting the body， then perhaps it is the brain that needs resting？ This might be a plausible hypothesis were it not for two factors. First the electroencephalograph （which is simply a device for recording the electrical activity of the brain by attaching electrodes to the scalp） shows that while there is a change in the pattern of activity during sleep， there is no evidence that the total amount of activity is any less. The second factor is more interesting and more fundamental. Some years ago an American psychiatrist named William Dement published experiments dealing with the recording of eye-movements during sleep. He showed that the average individual's sleep cycle is punctuated with peculiar bursts of eye-movements， some drifting and slow， others jerky and rapid. People woken during these periods of eye-movements generally reported that they had been dreaming. When woken at other times they reported no dreams. If one group of people were disturbed from their eye-movement sleep for several nights on end， and another group were disturbed for an equal period of time but when they were no exhibiting eye-movements， the first group began to show some personality disorders while the others seemed more or less unaffected. The implications of all this were that it was not the disturbance of sleep that mattered， but the disturbance of dreaming.

    speculation n.  推測

    literally adv. 確實

    odd adj. 奇特的

    tissue n.  組織

    plausible adj. 似乎有理的

    hypothesis n.  假說

    electroencephalograph n.  腦電圖儀

    electrode n.  電極

    scalp n.  頭皮

    psychiatrist n.  精神病學家

    punctuate v.  不時介入

    jerky adj. 急動的

    disorder n.  失調(diào)

    implication n.  表明

    很清楚，睡眠必然具有某種作用。睡眠占去那么多時間，所以其作用似乎還是很重要。人們對睡眠作用的種種猜測，確實有數(shù)千年之久。一項使人對這個問題感到困惑的奇怪的發(fā)現(xiàn)是，睡眠在很大程度似乎并不僅僅是為了使身體得到休息。"休息"，從使肌肉得到放松等方面來看，只要稍微躺一躺，甚至坐一坐就能達到。人體組織在一定程度上有自我修補和自我恢復的能力，有張有弛地連續(xù)活動時，其功能最佳。事實上，睡眠狀態(tài)下仍有著基本的活動量，以防止肌肉活動停止。

    如果睡眠的功能不是在于使身體得到休息，那么也許是讓大腦得以休息？若不是下面兩點，這種假使似乎是有道理的。第一點，腦電圖記錄儀（不過是一種把電極接到頭皮上記錄腦電活動的儀器）顯示，人在睡眠時大腦活動的方式有變化，但沒有跡象表明，其活動總量有任何減少。第二點更有意思，也更重要。前些年，美國一位精神病學者發(fā)表了一篇報告，報告中記錄了眼球在睡眠時的活動情況。他指出，平常人的睡眠周期中不時伴有一陣陣奇怪的眼球隊活動，這些活動有的飄忽而緩慢，有的急劇而快速。在眼球活動期間被叫醒的人都說自己在做夢；在其他期間叫醒他們，則說沒有做夢。如果有兩組人，一組人連續(xù)幾夜在眼球隊活動時被叫醒；另一組人也是連續(xù)幾夜被叫醒，但是在眼球隊沒活動時被叫醒的。結(jié)果，第一組人開始出現(xiàn)性格失常，而第二組人似乎沒受什么影響。這一切暗示我們：睡眠受到干憂沒關系，而做夢受到干憂是有問題的。