the 100 billion neurons in your skull conduct electrical signals to communicate and carry

你頭蓋骨中的一千億個神經元會在它們之間傳遞電訊號

messages between them, ultimately creating, well — YOU... and everything you do.

聯絡並傳送訊息，最終創造出，嗯 — 你... 以及你所做的一切

It's the most complex, essential and identifiable organ in the body, acting as the center of

大腦是體內最複雜、必要且好辨認的器官，在所有脊椎動物中

the nervous system in all vertebrates. But what if how you think and feel isn't just

扮演神經系統的中心。但如果你的所思所感並不只是

controlled by the brain and central nervous system, but in fact, a second brain that you

受控於腦和中樞神經系統，而其實是，還有你不曾知道的

didn't know about?

第二顆腦袋？

The brain uses the vagus nerve to connect and communicate with many parts of the body,

腦利用迷走神經去連結以及連絡身體的許多部位

including the vocal cords, heart, lungs and most of the digestive tract. It also uses

包括聲帶、心臟、肺臟還有消化道的大部分。腦也利用

this nerve to convey "fight or flight" messages to the body, which explains why you

這條神經傳送「戰或逃」訊息給身體，這解釋了你為什麼

might experience a cracking voice, racing heart, shortness of breath and a knot in your

可能經歷過破音、心臟狂跳、呼吸急促還有

stomach when you're really stressed or nervous. But while this extensive network is constantly

當你壓力很大或很緊張時覺得腸胃打結。但當這廣大的網路一直不斷地

sending signals from the brain to your body, scientists have noted that 80-90% of the nerve

從大腦傳遞訊息到你的身體，科學家注意到有 80 - 90%

fibers in the enteric nervous system are actually going from the gut to the brain.

腸道神經系統的神經纖維事實上正從腸道上行至腦

In fact, the enteric nervous system, which is an extensive mesh-like network of neurons

其實，腸道神經系統，控制了你從食道到肛門的整個消化道的

that controls your entire digestive tract from the esophagus to the anus, doesn't

廣大網狀神經元網路

even require the brain at all. When the vagus nerve is severed, the enteric nervous system

一點也不需要大腦。當迷走神經被切斷，腸道神經系統

is capable of organizing and initiating its own reflexes for digestion because it has

仍能夠組織並起始它自己的消化反射，因為它有

such a complex collection of neurons. It is your second brain, and controls you far

如此複雜的神經元集合。它就是你的第二個腦，而且它控制你

more than you realize.

遠比你所以為的還要多

From an evolutionary perspective — before modern food safety protocols — our biggest

從演化的觀點來看 — 在規範現代食品安全規則之前 — 我們最大的

choices were about eating. Is it safe? Will it make me sick? Will it give me energy? This

抉擇就是關於飲食。它安全嗎？它會致病嗎？它能給我能量嗎？

is why we would need a direct line of communication between the gut and the brain. For example,

這就是為什麼我們需要腸道和腦之間直接連線溝通。舉例來說，

fat and sugar are good sources of fuel for the body, so we have evolved mechanisms to

脂肪和醣類是身體很好的能量來源，所以我們發展出了

notify the brain to release the "feel-good" neurotransmitter dopamine when we eat foods

當我們吃到高脂質和醣類的食物時，通知腦袋釋放「感覺好」的神經傳導物質多巴胺的機制

high in fats and sugars, which make us continually seek them out.

這讓我們持續尋求這種食物

But the enteric nervous system becomes even more interesting when you realize that the

腸道神經系統更有趣的是，當你理解到

microbes in your gut actually produce over 50% of the dopamine found in your body, and

你體內的多巴胺有超過 50% 其實是由腸道中的微生物產生

90% of the serotonin; two neurotransmitters that drastically affect your mood, happiness

以及 90% 的血清素；兩種會激烈影響情緒的神經傳導物質，使你高興和愉悅

and pleasure. And these microbes can manipulate your cravings and eating behaviours for their

而且這些微生物為了自己的存活可以操縱你的渴望和飲食習慣

own survival. Your diet affects which bacteria thrive, but as a result, the flourishing bacteria

你的飲食影響了哪種細菌可以存活，結果是，腸道繁茂的細菌

in your gut can then send signals to the brain via the vagus nerve to tell you to keep eating

可以藉由迷走神經傳遞訊息到腦，告訴你要繼續吃

the foods they love. This is why some scientists have suggested that treatment with probiotics

它們愛的食物。這就是為什麼一些科學家建議使用益生菌或

or fecal transplants could be an effective therapy for overeating; by getting rid of

糞便移植的治療可以是暴飲暴食的有效療法；藉由除掉

certain bacteria that generate intense cravings for high-fat and high-sugar foods.

會對高脂肪和高醣類食物產生熱切渴望的特定細菌

In fact, current research is pointing to a gut with healthy microbiomes as a strong predictor

事實上，現今的研究指出腸道擁有健康微生物群系即是預告了

of emotional and mental health. Mice raised in sterile environments, where no bacteria

情緒和精神健康。在無菌環境中飼養的小鼠，沒有細菌

could colonize their gut, exhibit social traits similar to those seen in humans on the autism spectrum.

可在牠們的腸道中定植，表現出類似於在自閉症譜系上的人類的社交特性

When researchers studied their brains, they also found significant changes in the

當研究員研究牠們的腦袋，他們還發現了

levels of serotonin and specific proteins related to learning and memory formation.

血清素以及與學習和記憶形成相關的特定蛋白量有重大變化

But after feeding the mice with specific probiotics to help cultivate healthy microbiomes,

但在餵給老鼠幫助培養健康微生物群系的特定益生菌後

the symptoms were alleviated. Their gut controlled their behaviour!

症狀緩和了。牠們的腸道控制了行為！

A 30-day study comparing people who ate probiotic yogurt found a decrease in the levels of anxiety

一項 30 天的研究發現吃益生菌優格的人焦慮和憂鬱的程度下降

and depression compared to people who consumed milk with no bacteria.

相較於喝無菌牛奶的人們

And another study found that mice fed a specific bacteria had less stress-related hormones

而另一項研究發現餵食一種特定細菌的小鼠血中有較少壓力相關的激素

in their blood and performed better on tests of learning and memory. But when researchers

並且在學習和記憶的測試中表現較好。但當研究員

severed the vagus nerve, all of these improvements disappeared. Again, their guts were in control

剪斷迷走神經，所有這些進步都消失了。又一次，牠們的腸道掌控了

of their emotions!

牠們的情緒！

Studies have even shown that stimulating the vagus nerve at different frequencies, by implanting

研究甚至顯示了在不同頻率刺激迷走神經，藉由植入

a small pacemaker, can help patients with treatment-resistant depression, by mimicking

一個小型心律調節器，可以模擬有健康腸道人類的迷走神經活性

vagal nerve activity like a person with a healthy gut.

幫助治療無效的憂鬱症患者

And the essential role of the gut doesn't end there. Given that large social groups

腸道的重要角色還沒有結束。有鑑於大型社會團體

increase the potential of one's genes being passed on — for both us and our bacteria —

增加了一個人的基因被傳承的潛能 — 對我們和我們的細菌都是 — 研究員

researchers now believe that the function of the microbiome is partly to promote pro-social behaviours.

現在相信微生物群系的功能有部分是促進親社會行為

Healthy gut bacteria can lead to a higher resilience of negative emotions from others,

健康的腸道細菌可使從負面情緒恢復的能力較好

which makes you more forgiving and better at fostering strong social connections, ultimately

這使你更加寬恕並且較善於培養強烈社交感情，最終

improving your shot at reproduction.

促進你繁衍後代的成功率

All thanks to your second brain!

全都多虧了你的第二大腦！

Special thanks to Audible for supporting this episode

特別感謝 Audible 支持這部影片

to give you a free 30 day trial at audible.com/asap.

在 audible.com/asap 給你們 30 天免費試用

This week, we wanted to recommend the book "How Not To Be Wrong:

本周，我們想要推薦「數學教你不犯錯：

the power of mathematical thinking", which helped us create our

不落入線性思考、避免錯誤推論」這本書，幫助我們創作

previous episode, "Are good looking people jerks?"

前一集影片「外表好看的人都是壞人嗎？」

It's an awesome read. You can get a free 30-day trial at audible.com/asap, and choose from massive selection.

這是本很好看的書。你可以在 audible.com/asap 得到 30 天免費試用以及大量的選擇

We love them as they're great when you're on the go. And subscribe for more weekly science videos!

我們愛用它因為當你忙碌時它們很好用。訂閱看更多每周的科學影片！