Do we only use 10% of our brains

We love the idea that we could be much more intelligent or creative if we harnessed unused parts of our minds. Sadly, Claudia Hammond has some bad news.

It’s amazing just how many medical myths there are to choose from, but one part of the body seems to attract more than its fair share, and that’s the brain. One of my favourite brain myths is the idea that we only use 10% of it. It’s an appealing idea because it suggests the possibility that we could become so much more intelligent, successful or creative, if only you could harness that wasted 90%. This might inspire us to try harder, but unfortunately that doesn’t mean there’s any truth in it.

First of all, it’s important to ask the question – 10% of what? If it is 10% of the regions of the brain to which people are referring, this is the easiest idea to quash. Using a technique called functional magnetic resonance imaging, neuroscientists can place a person inside a scanner and see which parts of the brain are activated when they do or think about something. A simple action like clenching and unclenching your hand or saying a few words requires activity in far more than a tenth of the brain. Even when you think you are doing nothing your brain is doing rather a lot – whether it’s controlling functions like breathing and heart rate, or recalling the items on your to-do list.

But maybe the 10% refers to number of brain cells. Again this doesn’t work. When any nerve cells are going spare they either degenerate and die off or they are colonised by other areas nearby. We simply don’t let our brain cells hang around idly. They’re too valuable for that. In fact our brains are a huge drain on our resources. Keeping brain tissue alive consumes 20% of the oxygen we breathe, according to cognitive neuroscientist Sergio Della Sala.

It is true that nature can sometimes involve some strange designs, but to evolve to have a brain ten times the size we needed would seem very odd, when its large dimensions are so costly to our survival, leading on occasion to obstructed labour and the death of a mother during childbirth if no help is available.

Yet many people do cling on to the idea that we only use 10% of our brains. The idea is so prevalent that when the University College London neuroscientist Sophie Scott was on a first aid course the tutor assured the class that head injuries are not very serious because of the 10% “fact”. He was not only wrong about the 10%, but he was also wrong about the impact of brain damage. Even a small injury can have huge effects on a person’s capabilities. The first aid tutor probably wasn’t bargaining on instructing a professor of neuroscience on the course, but Scott put him right.

Head scratcher

So how can an idea with so little biological or physiological basis have spread so widely? It is hard to track down an original source. The American psychologist and philosopher William James mentioned in The Energies of Men in 1908 that we “are making use of only a small part of our possible mental and physical resources". He was optimistic that people could achieve more, but he does not refer to brain volume or quantity of cells, nor does he give a specific percentage. The 10% figure is mentioned in the preface to the 1936 edition of Dale Carnegie’s best-selling book How to Win Friends and Influence People, and sometimes people say that Albert Einstein was the source. But Professor Della Sala has tried to find the quote, and even those who work at the Albert Einstein archives can find no record of it. So it seems this might be a myth too.

There are two other phenomena that might account for the misunderstanding. Nine-tenths of the cells in the brain are so-called glial cells. These are the support cells, the white matter, which provide physical and nutritional help for the other 10% of cells, the neurons, which make up the grey matter than does the thinking. So perhaps people heard that only 10% of the cells do the hard graft and assumed that we could harness the glial cells too. But these are different kind of cells entirely. There is no way that they could suddenly transform themselves into neurons, giving us extra brain power.

There is a very rare group of patients whose brain scans reveal something extraordinary, though. In 1980, a British paediatrician called John Lorber mentioned in the journal Science that he had patients with hydrocephalus who had hardly any brain tissue, yet could function. This doesn’t of course show us that the rest of us could make extra use of our brains, just that these people have adapted to extraordinary circumstances.

It is, of course, true that if we put our minds to it we can learn new things, and there is increasing evidence in the area of neuroplasticity showing that this changes our brains. But we are not tapping into a new area of the brain. We create new connections between nerve cells or lose old connections that we no longer need.

What I find most intriguing about this myth is how disappointed people are when you tell them it’s not true. Maybe it’s the figure of 10% that is so appealing because it is so low that it offers massive potential for improvement. We’d all like to be better. And we can be better if we try. But, sadly, finding an unused portion of our brains isn’t the way it’s going to happen.

译文：

如果我们能够善用头脑里还未开发的部分，我们可以变得更有智慧，更加有创新性，所有人都乐见此事。可惜的是，克劳迪娅·哈蒙德给我们带来了一个坏消息。

    有多少医学假说可以给我们挑选研究，数量实在令人叹为观止。但是，身体的某一部位似乎吸引了更多目光，也许这并不公平。对了，就是大脑。我最喜欢的一个有关大脑的假说就是我们只利用了大脑的10%。这个想法很有诱惑力，因为它暗示了这种可能性，只要你能将浪费的90%的部分善加利用，我们就有可能变得更有智慧，更加成功，或者更有创新性。这有可能激励我们更加努力，但是，不幸的是，这种假说毫无道理可言。

    首先一点，我们要问一个很重要的问题。——什么的10%？如果人们指的是大脑区域的10%，那么要驳倒这个想法就再容易不过了。利用一个我们叫做功能性磁共振成像的技术，神经学家可以观察机器扫描的图像来确定当人们思考某事的时候，大脑的哪个部分处于活跃状态。一个像紧握或者松手这样的简单动作或者像说几个词语这样的简单过程，大脑的活跃范围也远远超过了十分之一。即使你百无聊赖，你的大脑却在忙前忙后——它或许正在控制呼吸或者心率这样的功能，或者在回想你想要做的事情。

    也许10%指的是大脑细胞。但事实却并不如此。当有多余的神经细胞时，它们要么退化后相继死亡，要么被附近其它的地方征调。原因很简单，我们的大脑细胞不会无所事事，否则付出的代价实在太大了。事实上，我们的大脑消耗了我们巨大的资源。根据神经学家塞尔吉奥.黛拉.撒拉的说法，让脑组织本身活着就需要我们所呼吸的氧气的20%。

    毋庸置疑，自然有时确实会造就奇怪的设计。但是如果进化出的大脑的大小是我们所需要的10倍，着实令人奇怪，这样的大家伙对于我们生存来说实在太费事了，结果就是，在没有帮助的情况下，在生产时，母亲可能难产甚至死亡。

    但是仍然有很多人紧盯我们只利用了大脑的10%这个说法不放。这个说法在英国伦敦大学学院的神经学家索菲.斯科特参加的急救课程上弥漫开来，某位急救老师在一次急救课程培训课程中保证，就算头部受伤也不是什么大事，因为“事实上”，我们只利用了大脑的10%。它不仅在10%这个数值犯了错误，但他也对大脑损伤影响的评估也大错特错。即使一个小小的损伤也会对人类的功能拥有巨大的影响。这位急救老师可能并不妄图在课程上去指导一位神经学教授，而斯科特立即辟了谣。

    一个头痛的问题

    那么这样一个毫无生物学或者生理学基础的想法怎么会广为传播呢？追根溯源变得很困难。美国生理学家、哲学家威廉.詹姆斯在1908年的《男人的力量》一书中讲到，我们“正在利用的脑力和生理资源只占可利用资源的一小部分”。他对于我们能够成就更多表示乐观，但没有给出一个具体的百分比。10%的数据在1936年版的由戴尔·卡耐基写的畅销书《如何赢得朋友和影响别人》序言中有所提及，有时，人们说爱因斯坦是这个说法的由来。但是黛拉.撒拉教授试图找到引证，但是那些有关阿尔伯特·爱因斯坦的档案没有留下蛛丝马迹。所以，似乎这也成了一团迷雾。

    还有另外两个现象造成了这个误解。大脑里十分之九的细胞是所谓的胶质细胞。这些后勤细胞——脑白质，给其它10%的细胞——神经细胞，提供了生理和营养支持，神经细胞除了支持思考功能外也是灰质的组成部分。也许人们听说只有10%的细胞发挥功能，并且还提出了假设说我们胶质细胞也能善加利用。但是这些是完全不同的细胞种类。一下子将他们转变为神经细胞，给我们大脑带来额外的动力，是完全不可能的。

    虽然这样说，还是有一小群患者在大脑扫描中显示了他们的与众不同。在1980年，一位名叫约翰.罗伯英国的儿科专家在科学杂志中提到，他的脑积水患者几乎没有大脑组织，但也行动自如。当然，这并不是说其他人也能利用大脑的额外功能，只是说明了这些人已经适应了非常情况。

    当然啦，如果我们花大力气研究这个领域，我们会学到新东西，在神经可塑性领域，越来越有迹象表明它可以改变我们的大脑。但是我们并没有涉及大脑的新领域。我们只是在神经细胞之间或者创造了新的联系，或者摈弃了我们不再需要的旧有联系。

    我们在这个假说上发现的最有趣的情况是，当你告诉人们这个假说无法成立时，别提人们有多失望了。也许是10%的数据太有吸引力了，它为提升提供了巨大的潜能。我们都希望变得更好，如果我们努力的话，我们都希望做到。但是，遗憾的是，找到了大脑未被利用的部分并不意味着奇迹就会发生。