The Stuff of Dreams

It is fairly clear that the sleeping period must have some function, and because there is so much of it the function would seem to be important. Speculations about its 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, 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. In 1960 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 by peculiar bursts of eye - movements, some slow, some rapid, some in both directions. These periods of eye - movements are called REM sleep (Rapid Eye Movement) periods, and they occur at intervals of about 90 minutes throughout the night with an average duration of about 20 minutes. People woken during these periods of REM sleep generally report that they have 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 number of nights but when they were not experiencing eye - movement sleep, the first group began to show some personality disorders while the second group did not. REM sleep seems to be essential for the normal functioning of the brain. REM sleep occurs in both humans and animals. Some animals, such as cats, have large amounts of REM sleep, while others, such as cows, have very little. There is some evidence that the amount of REM sleep is related to the intelligence of the animal. The more intelligent the animal, the more REM sleep it has. But why should REM sleep be essential for the normal functioning of the brain? One theory is that during REM sleep the brain is 'rehearsing' things that it has learned during the day. Another theory is that REM sleep is a time when the brain is 'clearing' itself of useless information. But neither of these theories has been proved yet. So far we have only been able to say that REM sleep seems to be essential for the normal functioning of the brain, and that the amount of REM sleep is related to the intelligence of the animal. We still do not know what the function of sleep is, or why we need to dream.

很清楚，睡眠必然具有某种作用。由于睡眠占去那么多时间，其作用似乎还很重要。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，睡眠在很大程度上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，睡眠期间仍有一定基本量的活动，这种活动特别与防止肌肉活动中断有关。如果睡眠的功能不是在于使身体得到休息，也许是大脑需要休息吧？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）表明，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。1960年，一位名叫威廉·迪蒙特的美国精神病学家发表了一篇报告，报告中记录了他对睡眠时眼球活动的研究情况。他指出，平常人的睡眠周期中不时穿插着一阵阵奇怪的眼球活动，这些活动有的慢，有的快，有的双向进行。这些眼球活动期间被称为快速眼动（REM）睡眠期，它们在一夜之间每隔大约90分钟发生一次，每次平均持续约20分钟。在快速眼动睡眠期间被叫醒的人一般都说自己在做梦；在其他时间叫醒他们，则说没有做梦。如果有一组人连续几夜在其眼球活动期间被叫醒，而另一组人也是连续几夜被叫醒，但是在其眼球没有活动期间被叫醒，结果，第一组人开始出现一些性格失常，而第二组人则没有。快速眼动睡眠看来对大脑的正常功能是必不可少的。快速眼动睡眠在人和动物身上都会发生。有些动物，如猫，有大量的快速眼动睡眠；而另一些动物，如牛，则有很少的快速眼动睡眠。有证据表明，快速眼动睡眠的量与动物的智力有关：动物越聪明，快速眼动睡眠就越多。但是，为什么快速眼动睡眠对大脑的正常功能是必不可少的呢？一种理论认为，在快速眼动睡眠期间，大脑在“排练”它在白天学到的东西。另一种理论认为，快速眼动睡眠是大脑“清除”无用信息的时候。但这两种理论都尚未得到证实。到目前为止，我们只能说，快速眼动睡眠似乎对大脑的正常功能是必不可少的，而且快速眼动睡眠的量与动物的智力有关。我们仍然不知道睡眠的功能是什么，也不知道我们为什么需要做梦。