An enduring myth says we use only 10% of our brain,
一个经久不衰的迷思声称，我们只运用大脑的十分之一，
the other 90% standing idly by for spare capacity.
剩下的百分之九十只不过是备用的存储而已。
Hucksters promised to unlock that hidden potential with methods 'based on neuroscience,'
某些假行家声称可以用“基于神经科学”的方法来开发那90%的隐藏潜力，
but all they really unlock is your wallet.
但他们真正打开的不过是你的钱包。
Two-thirds of the public and nearly half of science teachers mistakenly believe the 10% myth.
三分之二的大众以及近半数的科学教师误以为人只能用十分之一大脑的声明是真的。
In the 1890s, William James, the father of American psychology, said, 'Most of us do not meet our mental potential.'
在19世纪90年代，威廉·詹姆斯，美国心理学之父，曾说：“我们大多数人是不能开发我们全部的脑力潜能。”
James meant this as a challenge, not an indictment of scant brain usage.
詹姆斯的话意味着这是一项挑战，而并非控诉我们大脑较少的使用率。
But the misunderstanding stuck.
但这个误会一直困扰着大家。
Also, scientists couldn't figure out for a long time the purpose of our massive frontal lobes or broad areas of the parietal lobe.
另外，在很长一段时间里，科学家们想不出我们脑内大量的额叶或大面积的顶叶的用途。
Damage didn't cause motor or sensory deficits, so authorities concluded they didn't do anything.
并且因为额叶和顶叶的损伤并不会引起运动或感觉神经的缺失，所以研究人员断定它们没有任何作用。
For decades, these parts were called silent areas, their function elusive.
几十年来，这些部位被称为沉默区域，它们真正的作用令人难以琢磨。
We've since learned that they underscore executive and integrative ability, without which, we would hardly be human.
我们既然已经知道它们重视执行和综合能力，所以一旦失去它们，我们几乎就失去了人类的基本能力。
They are crucial to abstract reasoning, planning, weighing decisions and flexibly adapting to circumstances.
它们对我们抽象推理的能力、规划、做决定和是否能很快的适应环境有着至关重要的作用。
The idea that 9/10 of your brain sits idly by in your skull looks silly when we calculate how the brain uses energy.
那个十分之九的大脑在你的脑袋里袖手旁观的理论，在我们计算大脑怎样消耗能量时显得毫无道理。
Rodent and canine brains consume 5% of total body energy. Monkey brains use 10%.
啮齿动物和犬齿动物的大脑会消耗身体总能量的5%。猴子使用其大脑的10%。
An adult human brain, which accounts for only 2% of the body's mass, consumes 20% of daily glucose burned.
成人的大脑，仅占全身质量的2%，每日却消耗20%的葡萄糖。
In children, that figure is 50%, and in infants, 60%.
而儿童消耗50%的葡萄糖，婴儿要消耗60%。
This is far more than expected for their relative brain sizes, which scale in proportion to body size.
这组数值远远超出了我们的预想，因为它们不同的大脑相对于整个身体的质量。
Human ones weigh 1.5 kilograms, elephant brains 5 kg, and whale brains 9 kg,
人的大脑重1.5公斤，大象大脑重5公斤，鲸鱼大脑重9公斤，
yet on a per weight basis, humans pack in more neurons than any other species.
然而在这每一公斤里面，人类的大脑比其他物种的大脑有更多的神经元。
This dense packing is what makes us so smart.
我们人类正是因为紧密排列的神经元才会如此聪明。
There is a trade-off between body size and the number of neurons a primate, including us, can sustain.
在体重和神经元数量之间有一个平衡点，这就是灵长类动物（包括我们人类）可以承受的数量。
A 25 kg ape has to eat 8 hours a day to uphold a brain with 53 billion neurons.
一个25公斤重的猿每天要进食8个小时，才能使装有530亿个神经元的大脑正常运作。
The invention of cooking, one and half million years ago, gave us a huge advantage.
烹饪的发明，那是大约150万年前的事情，在进化方面带给了我们巨大的优势。
Cooked food is rendered soft and predigested outside of the body.
煮熟的食物较为松软，且在入口前已经过预消化。
Our guts more easily absorb its energy.
我们的内脏更容易吸收它的能量。

Cooking frees up time and provides more energy than if we ate food stuffs raw
相比于我们吃生食物来说，烹饪节省时间并提供了更多的能量，
and so we can sustain brains with 86 billion densely packed neurons.
所以我们可以维持拥有860亿密集神经元的大脑的正常运转，
40% more than the ape. Here's how it works.
这比猿大脑内的神经元数量多出40%。下面是它的工作原理。
Half the calories a brain burns go towards simply keeping the structure intact
大脑消耗的一半卡路里都只是简单地为了保持大脑结构的完好无损，
by pumping sodium and potassium ions across membranes to maintain an electrical charge.
用钠离子和钾离子渗透过细胞膜来保持胞内电荷平衡。
To do this, the brain has to be an energy hog.
要做到这一点，大脑则必须有强有力的能量。
It consumes an astounding 3.4x10^21 ATP molecules per minute, ATP being the coal of the body's furnace.
大脑每分钟都令人震惊地消耗3.4x10^21个三磷酸腺苷（ATP）分子，三磷酸腺苷就好像支持我们身体燃烧的燃料。
The high cost of maintaining resting potentials in all 86 billion neurons
在所有860亿神经元里面，保持（细胞的）静息电位的高消耗，
means that little energy is left to propel signals down axons and across synapses,
意味着只剩下很少的一点能量来把信号送到神经轴突和神经突触，
the nerve discharges that actually get things done.
实际上是神经放电这个过程在真正起作用。
Even if only a tiny percentage of neurons fired in a given region at any one time,
即使只有很少一部分的神经元在任一时间的某一区域被发射，
the energy burden of generating spikes over the entire brain would be unsustainable.
在整个大脑内因生成峰值而产生的能量负担会使其不能长时间负荷。
Here's where energy efficiency comes in.
因此就需要高效利用能源。
Letting just a small proportion of cells signal at any one time,
只让一小部分的细胞在某一时间被发射出来，
known as sparse coding, uses the least energy, but carries the most information.
这个叫做稀疏编码的过程，仅用最少的能量，但却能承载最多的的信息。
Because the small number of signals have thousands of possible paths by which to distribute themselves.
因为少量的信号有成千上万种可能的路径来到达目的地。
A drawback of sparse coding within a huge number of neurons is its cost.
但稀疏编码在大量的神经元内却有一个缺点，那就是它的成本。
Worse, if a big proportion of cells never fire,
更糟糕的是，如果有大量的细胞从来没有被发射出去，
then they are superfluous and evolution should have jettisoned them long ago.
那它们都是多余的了，自然选择在很长时间以前就应该把它们摒弃了。
The solution is to find the optimum proportion of cells that the brain can have active at once.
解决办法是要去找到可以立刻激活大脑的最佳数量比例的细胞。
For maximum efficiency, between 1% and 16% of cells should be active at any given moment.
为使效率最大化，在任何时间，1%~16%之间的细胞应该被激活。
This is the energy limit we have to live with in order to be conscious at all.
这是我们为了意识的清醒必须容忍的能量限制。
The need to conserve resources is the reason most of the brain's operations must happen outside of consciousness.
大脑需要节约资源，这正是大部分大脑的运作都必须发生在意识以外的主要原因。
It's why multitasking is a fool's errand.
这就是为什么同时处理多项任务是很傻的差事。
We simply lack the energy to do two things at once, let alone three or five.
我们只是单纯缺乏同时做两件事情的能量，更不用说三件事甚至五件事情了。
When we try, we do each task less well than if we had given it our full attention.
当我们尝试同时处理多项任务的时候，每一项任务就会比我们全力以赴做一件事情的时候成效要差。
The numbers are against us. Your brain is already smart and powerful.
这些数字是反对我们同时执行多任务的。你的大脑已经够聪明强大了。
So powerful that it needs a lot of power to stay powerful.
它需要很多的能量才能保持如此强大。
And so smart that it has built in an energy-efficiency plan.
大脑是如此的聪明，它已然建立了一个能源效率计划。
So don't let a fraudulent myth make you guilty about your supposedly lazy brain.
所以不要让一个骗人的谎言，让你对你据说很懒惰的大脑感到愧疚。
Guilt would be a waste of energy.
罪恶感也是会浪费能源的。
After all this, don't you realize it's dumb to waste mental energy?
在这长篇大论之后，你难道没有意识到浪费精力是很傻的举动吗？
You have billions of power-hungry neurons to maintain. So hop to it!
你有数十亿饿的要命的神经元要维持。所以赶快让它正常运作起来吧！