In the third millenium BCE, Mesopotamian kings recorded and interpreted their dreams on wax tablets.
公元前三千年，美索不达米亚国王在蜡质石板上记录并解释了他们的梦。
A thousand years later, Ancient Egyptians wrote a dream book listing over a hundred common dreams and their meanings.
一千年之后，古埃及人写了一本关于梦的书，列出了一百多个日常的梦以及它们的解释。
And in the years since, we haven't paused in our quest to understand why we dream.
多年之后，我们从未停止过探索我们做梦的原因。
So, after a great deal of scientific research, technological advancement, and persistence,
所以，我们在经历了大量的科学研究、科技进步以及坚持不懈之后，
we still don't have any definite answers, but we have some interesting theories.
依旧没有任何确切的答案，但是我们已经发展了一些有趣的理论。
We dream to fulfill our wishes.
我们为了满足自己的愿望而做梦。
In the early 1900s, Sigmund Freud proposed that while all of our dreams, including our nightmares,
在19世纪早期，西格蒙德·弗洛伊德提出，虽然我们所有的梦，包括梦魇，
are a collection of images from our daily conscious lives,
都来自有意识的日常生活画面集，
they also have symbolic meanings, which relate to the fulfillment of our subconscious wishes.
但他们也有一些抽象意义，它和我们潜意识中的愿望满足感有关。
Freud theorized that everything we remember when we wake up from a dream
弗洛伊德提出，我们从梦中醒来记得的所有事情
is a symbolic representation of our unconscious primitive thoughts, urges, and desires.
都是无意识的原始想法、冲动、以及欲望的象征性代表。
Freud believed that by analyzing those remembered elements,
弗洛伊德相信，通过分析我们记得的这些元素，
the unconscious content would be revealed to our conscious mind,
那些无意识的内容可以反映出我们有意识的思想，
and psychological issues stemming from its repression could be addressed and resolved.
精神上受到的压抑可以被理解和解答。
We dream to remember.
我们做梦是为了记忆。
To increase performance on certain mental tasks, sleep is good, but dreaming while sleeping is better.
为了加强一些脑力工作上的表现，睡眠非常有效，然而睡觉时做梦效果会更好。
In 2010, researchers found that subjects were much better at getting through a complex 3-D maze if they had napped and dreamed of the maze prior to their second attempt.
2010年，研究人员发现，如果被试者在第二次尝试穿越迷宫之前小憩一会儿并且做了一会儿梦的话，他们在穿越一个复杂的三维迷宫时会表现更佳。
In fact, they were up to ten times better at it than those who only thought of the maze while awake between attempts,
事实上，他们比那些在两次之间醒着思考迷宫的人，
and those who napped but did not dream about the maze.
以及那些虽然睡了但是没有做梦的人表现要好十多倍。
Researchers theorize that certain memory processes can happen only when we are asleep,
研究者推断，特定的记忆过程只在我们睡着时才会发生，
and our dreams are a signal that these processes are taking place.
而我们的梦是一个触发这些过程的信号。
We dream to forget.
我们做梦是为了遗忘。
There are about 10,000 trillion neural connections within the architecture of your brain.
我们的大脑构造里有大约一万兆的神经连接。
They are created by everything you think and everything you do.
它们因你思考以及所做的所有事情而形成。
A 1983 neurobiological theory of dreaming, called reverse learning, holds that while sleeping,
1983年，一个关于梦的神经生物学理论提出逆向学习的概念，该理论认为我们在睡觉时，
and mainly during REM sleep cycles, your neocortex reviews these neural connections and dumps the unnecessary ones.
尤其是在快速眼动睡眠周期时，大脑新皮质会回顾这些神经连接并清理掉那些不需要的部分。
Without this unlearning process, which results in your dreams,
如果没有做梦来产生这种反学习的过程，
your brain could be overrun by useless connections and parasitic thoughts could disrupt the necessary thinking you need to do while you're awake.
你的大脑就会因无用连接而过度运转，同时无用的想法会干扰到你醒着的时候需要进行的必要思考。
We dream to keep our brains working.
我们为了保证大脑运转而做梦。
The continual activation theory proposes that your dreams result from your brain's need to constantly consolidate and create long-term memories in order to function properly.
持续激活理论提出，你做梦是由于你的大脑为了有效运转需要持续不断地巩固和创造长期记忆。
So when external input falls below a certain level, like when you're asleep,
因此，当外界的输入低于一个特定水平时，例如你在睡觉时，
your brain automatically triggers the generation of data from its memory storages,
你的大脑会自动触发记忆库里的数据形成，
which appear to you in the form of the thoughts and feelings you experience in your dreams.
而这些在你看来就是你在梦里的想法和感受。

In other words, your dreams might be a random screen saver your brain turns on so it doesn't completely shut down.
换句话说，你的梦也许是个大脑运转时的随机保护程序，所以大脑并不会完全停止运转。
We dream to rehearse.
我们为了预演而做梦。
Dreams involving dangerous and threatening situations are very common,
梦经常包含危险和恐怖的情景，
and the primitive instinct rehearsal theory holds that the content of a dream is significant to its purpose.
而原始本能理论认为梦的内容对于它的目的来说非常重要。
Whether it's an anxiety-filled night of being chased through the woods by a bear or fighting off a ninja in a dark alley,
无论是一个在森林中被熊追着跑的紧张夜晚，还是在幽暗的山谷中击退一个日本武士，
these dreams allow you to practice your fight or flight instincts and keep them sharp and dependable in case you'll need them in real life.
这些梦允许你锻炼战斗或逃跑的本能，而且保证万一在现实中需要它们时，能保持一定的敏锐度和可靠性。
But it doesn't always have to be unpleasant.
不过梦也不一定总是不愉快的。
For instance, dreams about your attractive neighbor could actually give your reproductive instinct some practice, too.
比如，梦到你魅力无限的邻居可能会给你的生殖本能带来一定的锻炼。
We dream to heal.
我们为了治愈而做梦。
Stress neurotransmitters in the brain are much less active during the REM stage of sleep,
压力神经传导物质在快速眼动睡眠时期会表现得非常不活跃，
even during dreams of traumatic experiences,
即使是梦到受伤的经历，
leading some researchers to theorize that one purpose of dreaming is to take the edge off painful experiences to allow for psychological healing.
这一现象导致研究人员推测梦的一个目的是减弱不好经历带来的痛苦，以达到心理治疗的目的。
Reviewing traumatic events in your dreams with less mental stress may grant you a clearer perspective
在梦中以更小的精神压力回顾创伤性事件，可能会给你一个更加清晰透彻的看法，
and enhanced ability to process them in psychologically healthy ways.
以及增强你积极乐观地面对它们的能力。
People with certain mood disorders and PTSD often have difficulty sleeping,
有特定情绪失常和创伤后应激障碍的人可能很难入睡，
leading some scientists to believe that lack of dreaming may be a contributing factor to their illnesses.
这一现象导致一些科学家开始相信，缺乏做梦可能是加重他们病情的一个因素。
We dream to solve problems.
我们为了解决问题而做梦。
Unconstrained by reality and the rules of conventional logic,
不受现实生活和常规逻辑的约束，
in your dreams, your mind can create limitless scenarios to help you grasp problems
你的梦可能会产生无限的场景来帮助你把握问题，
and formulate solutions that you may not consider while awake.
以及形成你醒着的时候完全不会考虑到的解决方法。
John Steinbeck called it the committee of sleep,
约翰·斯坦贝克把它称为睡眠委员会，
and research has demonstrated the effectiveness of dreaming on problem solving.
而研究人员也已证实做梦在解决问题上的有效性。
It's also how renowned chemist August Kekule discovered the structure of the benzene molecule,
这也就是为什么著名的化学家奥古斯特·凯库勒发现了苯分子的结构，
and it's the reason that sometimes the best solution for a problem is to sleep on it.
也是为什么有些时候解决一个问题的最好办法就是睡一觉。
And those are just a few of the more prominent theories.
这里也有一些更为突出的理论。
As technology increases our capability for understanding the brain,
当科技增强了我们理解大脑的能力之后，
it's possible that one day we will discover the definitive reason for them.
有一天我们有可能会发现梦存在的真正原因。
But until that time arrives, we'll just have to keep on dreaming.
但是直到那一天到来之前，我们仍旧需要不停地做梦。