An enduring myth says we use only 10% of our brain, the other 90% standing idly by for spare capacity. Hucksters promised to unlock that hidden potential with methods "based on neuroscience," but all they really unlock is your wallet. Two-thirds of the public and nearly half of science teachers mistakenly believe the 10% myth. In the 1890s, William James, the father of American psychology, said, "Most of us do not meet our mental potential." James meant this as a challenge, not an indictment of scant brain usage. But the misunderstanding stuck. Also, scientists couldn't figure out for a long time the purpose of our massive frontal lobes or broad areas of the parietal lobe. Damage didn't cause motor or sensory deficits, so authorities concluded they didn't do anything. For decades, these parts were called silent areas, their function elusive. We've since learned that they underscore executive and integrative ability, without which, we would hardly be human. They are crucial to abstract reasoning, planning, weighing decisions and flexibly adapting to circumstances. The idea that 9/10 of your brain sits idly by in your skull looks silly when we calculate how the brain uses energy. Rodent and canine brains consume 5% of total body energy. Monkey brains use 10%. An adult human brain, which accounts for only 2% of the body's mass, consumes 20% of daily glucose burned. In children, that figure is 50%, and in infants, 60%. This is far more than expected for their relative brain sizes, which scale in proportion to body size. Human ones weigh 1.5 kilograms, elephant brains 5 kg, and whale brains 9 kg, yet on a per weight basis, humans pack in more neurons than any other species. This dense packing is what makes us so smart. There is a trade-off between body size and the number of neurons a primate, including us, can sustain. A 25 kg ape has to eat 8 hours a day to uphold a brain with 53 billion neurons. The invention of cooking, one and half million years ago, gave us a huge advantage. Cooked food is rendered soft and predigested outside of the body. Our guts more easily absorb its energy. Cooking frees up time and provides more energy than if we ate food stuffs raw and so we can sustain brains with 86 billion densely packed neurons. 40% more than the ape. Here's how it works. Half the calories a brain burns go towards simply keeping the structure intact by pumping sodium and potassium ions across membranes to maintain an electrical charge. To do this, the brain has to be an energy hog. It consumes an astounding 3.4 x 10^21 ATP molecules per minute, ATP being the coal of the body's furnace. The high cost of maintaining resting potentials in all 86 billion neurons means that little energy is left to propel signals down axons and across synapses, the nerve discharges that actually get things done. Even if only a tiny percentage of neurons fired in a given region at any one time, the energy burden of generating spikes over the entire brain would be unsustainable. Here's where energy efficiency comes in. Letting just a small proportion of cells signal at any one time, known as sparse coding, uses the least energy, but carries the most information. Because the small number of signals have thousands of possible paths by which to distribute themselves. A drawback of sparse coding within a huge number of neurons is its cost. Worse, if a big proportion of cells never fire, then they are superfluous and evolution should have jettisoned them long ago. The solution is to find the optimum proportion of cells that the brain can have active at once. For maximum efficiency, between 1% and 16% of cells should be active at any given moment. This is the energy limit we have to live with in order to be conscious at all. The need to conserve resources is the reason most of the brain's operations must happen outside of consciousness. It's why multitasking is a fool's errand. We simply lack the energy to do two things at once, let alone three or five. When we try, we do each task less well than if we had given it our full attention. The numbers are against us. Your brain is already smart and powerful. So powerful that it needs a lot of power to stay powerful. And so smart that it has built in an energy-efficiency plan. So don't let a fraudulent myth make you guilty about your supposedly lazy brain. Guilt would be a waste of energy. After all this, don't you realize it's dumb to waste mental energy? You have billions of power-hungry neurons to maintain. So hop to it!
有個歷久不衰的傳說 說我們只用了大腦的 10% 其餘的 90% 閒著備用 賣膏藥的人保證你能釋放潛能 用「有神經科學根據」的方法 但實際只釋放了你的錢包 三分之二的大眾 和近半的科學老師 誤信這 10% 的傳說 1890 年代,威廉‧詹姆士 美國心理學之父 說:「大部分的人都沒有充分發揮 他們的心智潛能」 詹姆士意指這是一個挑戰 而不是指控很少用腦 但這誤解延續至今 還有,科學家長久以來 都搞不清楚 我們巨大的額葉 或大面積的頂葉的功能 損傷並不會造成運動或感覺障礙 所以科學家斷定它們沒用 數十年來,這些部分 被稱為 「寂靜區域」 他們的功能令人費解 我們後來得知它們強調 執行及整合能力 沒有它們,我們稱不上是人類 它們對於抽像推理 計畫 衡量決定 及對各種情況的適應力非常重要 你的大腦十分之九 在顱腔內閒著的這個想法 看起來很蠢,如果我們計算 腦部如何使用能量 齧齒類及犬類的腦消耗 身體總能量的 5% 猴子的腦使用 10% 一個成年人的腦 只占身體總質量的 2% 卻消耗 20% 每日燃燒葡萄糖量 而孩童,這數字是 50% 而在嬰兒,60% 這比預期高出許多 與他們相對的腦容量而言 而腦容量與身體大小成正比 人類的腦重 1.5 公斤 大象的腦 5 公斤 而鯨魚的腦 9 公斤 而以重量比來看 人類裝了更多的神經元 比其他物種都多 這種高密度填充 就是我們如此聰明的原因 靈長類動物在身體大小 及能維持多少神經元之間 必須取得平衡,這也包括人類 一隻 25 公斤的猩猩每天要吃 8 小時 以維持牠腦內五百三十億個神經元 而發明烹調法 在 150 萬年前 給了我們巨大的優勢 煮熟的食物使之變軟而且已在身體外 先消化過了 我們的腸胃更容易吸收它的能量 煮食釋放出時間 及提供更多能量 比之於我們吃生食 所以我們才能維持腦內 八百六十億緊密填充的神經元 比猩猩還多 40% 這是它運作的方式 半數大腦燃燒的卡路里 拿去維持結構不變 由主動運輸鈉鉀離子 通過細胞膜以維持電荷來達成 要這樣做,大腦必須 是隻貪吃能源的豬 它每分鐘要消耗驚人的 3.4 x 10^21 個三磷酸腺苷分子 三磷酸腺苷是身體能源火爐的煤炭 要維持靜止電位的高代價 在全部八百六十億神經元中 意指只有所剩無幾的能量 能輸出信號到軸突及穿越突觸 造成神經放電,也就是任務完成 即使只有極少百分比的神經元 在某個時段某個區域被激發 其在整個大腦產生電衝動 所需的能量負擔 也是無法持續的 這是節能要起作用的地方 讓只有一小部分的細胞 在任何一段時間發送信號 這被稱為稀疏編碼 用最少的能量 但傳遞最多的訊息 因為這少數的信號 可以用數千種路徑 來傳遞 在這麼大量的神經元內 稀疏編碼有個缺點 就是成本很高 更糟的是,如果一大部分的 細胞從未被激發 那他們就是多餘的 演化早該在很久以前就把他們拋棄 解決的方法是找到 在某時刻內,腦內有多少 活躍的細胞的最佳比例 要獲得最大的效率 應該要有介於 1% 到 16% 間的細胞 在任一時刻處在活躍狀態 這是能量的限制 我們必須與之共存 這是為了能保持有意識狀態 腦部需要節約資源 正是絕大部分的腦部運作 都必須發生在意識以外的主要原因 這就是為什麼多工只是徒勞無功 我們就是沒有能量同時做兩件事 就別提三件或五件事了 當我們試著多工,我們每件事的成效 都比只專心做一件事要差 數字對我們不利 你的大腦已經很聰明,威力強大 如此強大,它需要很多能量 以保持強大 而且是如此聰明 它已經內建了一個節能計畫 所以不要讓一個不實的傳說 讓你對 本應懶惰的大腦感到愧疚 愧疚會浪費能量 在這長篇大論之後 你難道還不明瞭浪費心智能量 是件很蠢的事? 你有數十億 餓的要命的神經元要維持