Much of what we don't understand about being human is simply in our heads. The brain is a befuddling organ, as are the very questions of life and death, consciousness, sleep, and much more. Here's a heads-up on what's known and what's not understood about your noggin. -Jeanna Bryner

Sweet Dreams

If you were to ask 10 people what dreams are made of, you'd probably get 10 different answers. That's because scientists are still unraveling this mystery. One possibility: Dreaming exercises brain by stimulating the trafficking of synapses between brain cells. Another theory is that people dream about tasks and emotions that they didn't take care of during the day, and that the process can help solidify thoughts and memories. In general, scientists agree that dreaming happens during your deepest sleep, called Rapid Eye Movement (REM).

Slumber Sleuth

Fruit flies do it. Tigers do it. And humans can't seem to get enough of it. No, not that. We're talking about shut-eye, so crucial we spend more than a quarter of our lives at it. Yet the underlying reasons for sleep remain as puzzling as a rambling dream. One thing scientists do know: Sleep is crucial for survival in mammals. Extended sleeplessness can lead to mood swings, hallucination, and in extreme cases, death. There are two states of sleep - non-rapid eye movement (NREM), during which the brain exhibits low metabolic activity, and rapid eye movement (REM), during which the brain is very active. Some scientists think NREM sleep gives your body a break, and in turn conserves energy, similar to hibernation. REM sleep could help to organize memories. However, this idea isn't proven, and dreams during REM sleep don't always correlate with memories.

Phantom Feelings

It's estimated that about 80 percent of amputees experience sensations, including warmth, itching, pressure and pain, coming from the missing limb. People who experience this phenomenon, known as "phantom limb," feel sensations as if the missing limb were part of their bodies. One explanation says that the nerves area where the limb severed create new connections to the spinal cord and continue to send signals to the brain as if the missing limb was still there. Another possibility is that the brain is "hard-wired" to operate as if the body were fully intact - meaning the brain holds a blueprint of the body with all parts attached.

Mission Control

Residing in the hypothalamus of the brain, the suprachiasmatic nucleus, or biological clock, programs the body to follow a 24-hour rhythm. The most evident effect of circadian rhythm is the sleep-wake cycle, but the biological clock also impacts digestion, body temperature, blood pressure, and hormone production. Researchers have found that light intensity can adjust the clock forward or backward by regulating the hormone melatonin. The latest debate is whether or not melatonin supplements could help prevent jet lag - the drowsy, achy feeling you get when "jetting" across time zones.

Memory Lane

Some experiences are hard to forget, like perhaps your first kiss. But how does a person hold onto these personal movies? Using brain-imaging techniques, scientists are unraveling the mechanism responsible for creating and storing memories. They are finding that the hippocampus, within the brain's gray matter, could act as a memory box. But this storage area isn't so discriminatory. It turns out that both true and false memories activate similar brain regions. To pull out the real memory, some researchers ask a subject to recall the memory in context, something that's much more difficult when the event didn't actually occur.

Brain Teaser

Laughter is one of the least understood of human behaviors. Scientists have found that during a good laugh three parts of the brain light up: a thinking part that helps you get the joke, a movement area that tells your muscles to move, and an emotional region that elicits the "giddy" feeling. But it remains unknown why one person laughs at your brother's foolish jokes while another chuckles while watching a horror movie. John Morreall, who is a pioneer of humor research at the college of William and Mary, has found that laughter is a playful response to incongruities - stories that disobey conventional expectations. Others in the humor field point to laughter as a way of signaling to another person that this action is meant "in fun." One thing is clear: Laughter makes us feel better.

Nature vs. Nurture

In the long-running battle of whether our thoughts and personalities are controlled by genes or environment, scientists are building a convincing body of evidence that it could be either or both! The ability to study individual genes points to many human traits that we have little control over, yet in many realms, peer pressure or upbringing has been shown heavily influence who we are and what we do.

Mortal Mystery

Living forever is just for Hollywood. But why do humans age? You are born with a robust toolbox full of mechanisms to fight disease and injury, which you might think should arm you against stiff joints and other ailments. But as we age, the body's repair mechanisms get out of shape. In effect, your resilience to physical injury and stress declines. Theories for why people age can be divided into two categories: 1) Like other human characteristics, aging could just be a part of human genetics and is somehow beneficial. 2) In the less optimistic view, aging has no purpose and results from cellular damage that occurs over a person's lifetime. A handful of researchers, however, think science will ultimately delay aging at least long enough to double life spans.

Deep Freeze

Living forever may not be a reality. But a pioneering field called cryonics could give some people two lives. Cryonics centers like Alcor life Extension Foundation, in Arizona, store posthumous bodies in vats filled with liquid nitrogen at bone-chilling temperatures of minus 320 degrees Fahrenheit (78 Kelvin). The idea is that a person who dies from a presently incurable disease could be thawed and revived in the future when a cure has been found. The body of the late baseball legend Ted Williams is stored in one of Alcor's freezers. Like the other human popsicles, Williams is positioned head down. That way, if there were ever a leak in the tank, the brain would stay submerged in the cold liquid. Not one of the cryopreserved bodies has been revived, because that technology doesn't exist. For one, if the body isn't thawed at exactly the right temperature, the person's cells could turn to ice and blast into pieces.

Consciousness

When you wake up in the morning, you might perceive that the Sun is just rising, hear a few birds chirping, and maybe even feel a flash of Happiness as the fresh morning air hits your face. In other words, you are conscious. This complex topic has plagued the scientific community since antiquity. Only recently have neuroscientists considered consciousness a realistic research topic. The greatest brainteaser in this field has been to explain how processes in the brain give rise to subjective experiences. So far, scientists have managed to develop a great list of questions.

人类身体上的很多我们难以理解的谜存在于我们的大脑中。大脑是一个让人迷惑的器官,就像生和死、意识、睡眠和其他更多的东西,这都是人类关于人脑至今也没有解开的谜团。--Jeanna Bryner

1.梦境
如果问10个人同一个问题关于什么引起做梦,你可能会得到10种不同的答案。这是因为目前科学家还没有揭开这个谜底。一种可能是:做梦过程中通过刺激大脑分子间的信息神经键对大脑进行锻炼。另一个理论是,人们梦到白天不能顾及的任务和情感,这个过程可以帮助人们巩固思想和记忆。一般而言,科学家赞同梦境会在浅睡时发生的观点,他们称这一时期为雷姆期睡眠。

2.睡眠
果蝇要睡觉,老虎也要,人类似乎永远也睡不够。这里讨论的是睡眠的话题,人的一生要花费四分之一的时间睡觉。然而,睡觉的根本原因仍旧像天马行空的梦境一样让人不得费解。但科学家也确实了解睡眠的一个重要方面:睡觉对哺乳动物的生存至关重要。长期失眠能导致精神恍惚、幻觉,并最终引起死亡。睡眠的两种状态——深睡期(眼球活动减慢),此时脑部代谢活动放慢;浅睡期(此时会做梦),这一时期大脑活动活跃。某些科学家认为深睡期睡眠能让身体休息,保存精力,就像动物冬眠一样。浅睡期睡眠有助于把记忆的东西组织起来。然而这种观点没有得到证实,浅睡期做梦不总是与记忆有关。

3.幻觉
估计80%的截肢者都体验过来自断肢的包括温暖、渴望、压力和痛苦等感觉,经历这种现象(我们所知的“幻觉肢体”)的人,总是感觉到被截掉的肢体仍然存在。一种解释认为,断肢的神经区与脊髓重新建立了联系,好像缺少的肢体依然存在一样,继续向大脑发送信号。另一个可能是,大脑是一条传输“硬线”,它就像对待完美无缺的身体一样操纵残体——这意味着大脑仍然保存着肢体健全时的操纵蓝本。

4.任务控制
大脑丘脑下部的下丘脑视交叉上核或生物钟保持身体随着24小时的节奏运转。生理节奏引起的一个最明显的结果是:睡眠-醒来的循环,但是生物钟还影响着消化力、体温、血压和激素的产生。研究人员发现,通过增强光亮调节褪黑激素可以将生物钟向前或向后调整。最近人们不断争论,是否可以通过补充褪黑激素来帮助人们预防飞机时差——昏昏欲睡和飞机通过时区时产生的头痛感。

5.记忆途径
人生的某些经历很难忘却,就像你的初吻。但是一个人要怎样把握这些私人情景呢?科学家正在利用大脑成像技术设法弄清楚创造记忆和储存记忆的机械反映。他们发现大脑灰质内部的海马体能充当记忆储存箱的功能。但是这个储存区域的分辨能力并不强。对相同的大脑区域的刺激,可以让它产生真实的和虚假的记忆。为了把真实记忆从虚假记忆中脱离出来,研究人员提出根据背景回忆以加强记忆的方法,如果某些事情没有真正发生过,就很难通过这种方法加强人脑对它的记忆。

6.取悦大脑
笑是人类最难理解的行为之一。科学家发现,当人们开怀大笑时,大脑内部有三个部位变的活跃起来,它们是:管辖思维的区域,它让你获得笑料;运动区域促使你的肌肉运动;情感区域引出“轻佻的”情绪,让人露出笑容。但是为什么某人会因兄弟愚蠢的笑话John Morreall而发笑,而另一些人会在看恐怖影片时咯咯大笑。约翰·莫利尔是威廉与玛丽学院 幽默研究的先驱,他发现,笑声是对违反常规的不协调的故事的一个十分有趣的反映。幽默领域的另一个观点把笑看作向其他人发出这种行为很“有趣”的信号的一条途径。从而可以看出:笑让我们感觉更好。

7.天生与营养
我们的思想和个性是否是由基因或环境控制的问题,长期以来一直争论不休。科学家建立了一个让人信服的证据体系,证明它可能是受其中之一控制或者是由两方面同时控制。研究个体基因的能力显示出我们对很多人类特性无法控制,然而在很多领域,同辈人面对的压力或接受的教育会对我们是什么样的人以及我们将做什么产生深远影响。

8.死亡之谜
长命百岁是好莱坞电影中才会发生的事情。但是我们为什么会变老?你出生时像一个精力充沛的工具箱,体内充满各种抵抗疾病和修复创伤的机制,也许你认为,仅凭这些就能让你抵抗关节僵硬和其他疾病。但是随着我们不断变老,身体的修复机制渐渐失去往日的功效。事实上,你的身体恢复创伤和压力的能力正随着年龄的增加不断下降。人的老化被分成两个种类的学说:1)像人类的其他特征,变老可能是人类遗传学的一部分,并且从某些方面来说对人类有益。2)以最不乐观的观点来看,变老不是有意图的,人的一生中细胞不断受到损害从而引起人体老化。大量研究人员认为,科学将最终推迟变老速度,使人类寿命至少可以达到预期生命期限的两倍。

9. 人体冷冻
要求长命百岁可能并不现实。但是一个被称作人体冷冻学的新领域将会让某些人死而复生。人体冷冻学中心如亚利桑那州的Alcor生命延工基金会在充满液态氮并且温度为华氏零下320度(78绝对温度)的刺骨的容器中储藏死者的遗体。这个想法的目的是,死于目前无法治愈的疾病的人在将来发现治愈方法后可以通过解冻让他们死而复生。最近, 棒球传奇人物Ted Williams 被储存在Alcor的一个冷藏柜中。像其他人体“冰棒”一样,Williams被头朝下放置。这种放置方式的好处是,如果容器发生泄漏,大脑仍能保存在冰冷的液态里。到目前为止还没有一具被保存的尸体重获新生,这是因为这种让人重获新生的技术还不存在。举例来说,如果尸体没在适宜的温度下解冻,人体细胞就会结冰,导致受损破碎。

10.意识
清晨一觉醒来,你可能就已经意识到太阳刚刚升起,听到一些鸟儿在枝头欢快的鸣叫,甚至清新的空气轻拂你的面颊,你会感到一有幸福感。换句话说,你是有意识的。这个复杂的话题从一开始就困扰着科学界。最近,神经学家才把意识作为一门现实的研究课题。此领域的最大谜团已被解析为大脑中的程序是如何引起自觉的经验。至今为止,科学家们已经成功拓展出一大套相关问题的清单。