But if you find yourself staring at the half-eaten donut in your hand saying,

但如果你發現自己正盯著手裡吃到一半的甜甜圈，問自己

" Why can't I quit you?”, don’t beat yourself up too much.

「為什麼我沒辦法戒掉你呢？」，別對自己要求太苛刻了

New research out this week suggests that our brains are hardwired to love that donut.

本周有新研究顯示，人類的大腦構造，讓我們對那個甜甜圈無法抗拒

Writing in the publication Cell, scientists at MIT say that they’ve discovered the neural circuits

麻省理工學院研究人員近期在學術期刊《細胞》中表示，他們已經發現了

that controls sugar and food addictions.

控制甜食上癮機制的神經迴路

It’s called the LH-VTA Loop, and it’s like a highway between the lateral hypothalamus,or LH,

它被稱作 LH-VTA Loop，很像一座高速公路

which controls how hungry you feel, and the eventual tegmental area, or VTA,

建造在控制飢餓感的側下視丘 (LH) 。還有腹側膜區，又被稱作 VTA 之間

which is the center of the brain’s reward circuit.

用來控制大腦反饋機制的中心

Scientists knew that the LH-VTA Loop existed --

科學家確知 LH-VTA Loop 是存在的，因為當這個區域出現問題

problems in this area have been linked to some sexual and drug addictions.

可以和某些性、藥成癮扯上關係

But they didn’t know if it was responsible for food addiction, as well.

但是他們不能確定這個部位是否也控制了飲食成癮

So to test its role in eating behavior, they used a technique called optogenetics, on mice.

為了檢測它在飲食行為中的角色，他們用了一種叫光遺傳學的技術，對老鼠做實驗

They genetically modified certain neurons in the mice’s brains,

他們對老鼠腦部的一些神經元作了基因修改

so that those cells could be basically turned on or off by exposing them to light.

於是當暴露於燈光下。這些細胞的感應就能被打開或關閉

By delivering a yellow light through a small, implanted fiber optic,

透過一條細小的光纖，傳送黃色的光

the scientists could turn those neurons on and activate the LH-VTA Loop.

科學家可以打開該神經元並促使 LH-VTA Loop 進入活動狀態

They could also turn those same neurons off by delivering a blue light.

他們也能夠透過傳送藍色的光來關閉這些神經元

With these modifications in place, healthy, well-fed mice were put into two stations.

經過這些基因修改後，健康、且已餵飽的老鼠被放置到兩個組別中

The first had a cup full of food pellets, and the second had a sugar dispenser.

第一組放置了一杯食物，第二組有個糖分供應機

The scientists then activated the yellow light.

此時科學家傳送了黃色的光

With their reward circuits stuck in the “on” position, the mice ate for longer periods of time in the first station,

當他們的大腦迴路處於打開狀態，第一組老鼠吃得時間比較長

and kept going back to the sugar dispenser, repeatedly, at the second station.

而第二組老鼠則是反覆的去接觸糖分供應機

The mice at the second station would even walk across a platform that delivered electrical shocks

第二組的老鼠甚至會穿越一道發出電擊的平台

just to get more of that sweet stuff.

就為了要吃更多的甜食

But when the scientists used the blue light to turn off the LH-VTA Loop,

但當科學家用藍光把 LH-VTA Loop 關上

the mice wouldn’t walk across the electrified platform, and they wouldn’t eat if they were full.

老鼠再也不會越過電擊平台，飽足時也不再吃任何東西

Now, we humans also have this same Loop in our brains, and it’s likely there for a reason.

而在人類大腦中，我們也有一樣的迴路，想必有其作用

Many scientists believe that our taste for what we now think of as junk food

許多科學家認為那些我們所說的垃圾食物

evolved as a way to reward us for finding palatable, high-energy food when food was scarce.

能在食物不足時，能供給我們高熱量，並透過腦內的反饋機制帶給我們愉悅感

But, because we now live in a world with a Krispy Kreme on every corner,

但由於我們現在身處於一個隨地可見到 Krispy Kreme 的時代

our desire for sugar has become more of a hindrance than a help.

我們對糖分的欲望讓腦內的反饋機制受到了阻礙

So, the scientists say that finding the part of our brain that regulates these cravings.

因此，科學家認為找到我們大腦中控制這些欲望的部分

can help in developing treatments for often-debilitating food addictions.

就可以幫助我們研發治療食物成癮的方式

But, besides our brain’s reward system, what else makes us love food?

但除了大腦的反饋機制以外，還有什麼使我們熱愛食物呢？

Well, taste, of course.

無庸置疑，就是味覺

There’s bitter, sweet, salty, sour and what’s sometimes called the ‘fifth’ taste,

味覺包含了苦、甜、鹹、酸，有時還有「第五味」

known as umami.

稱為「鮮味」。

It’s best described as a savory -- but not salty -- flavor that you can’t quite put your finger on.

可口開胃，但並非鹹味，是最好的描述。這是個你無法確切形容的味道

Umami flavor comes predominantly from high levels of the amino acid glutamated

鮮味主要來自於高度精練的谷氨酸鹽

and was discovered by a Japanese scientist in 1908.

1908 年由日本科學家發現

It’s found in cheeses, shiitake mushrooms, ham, and monosodium glutamate,

在起司、香菇、火腿、還有味素

a food additive that was developed in 1909 to enhance the umami flavor of food.

1909 年發明的一種提味用調味品，這些當中都有鮮味

Now, according to a new study in Japan, tasting umami might be important to our health.

如今，根據日本新研究，嘗鮮味對我們的健康可能相當重要

Scientists performed what’s known as a paper filter disk test on 44 elderly patients.

科學家對 44 名成年病患做了這個稱為「濾紙圓盤法」的實驗

The test uses a small piece of paper soaked in different concentrations of a tasty solution,

他們把小張的濾紙浸在各種味道的濃縮溶液裡

place on the parts of the tongue responsible for each taste.

然後將它們放置於舌頭上對應該味覺的部分

And 16 percent of those tested turned out to have unusually high thresholds for umami,

他們發現有 16% 的受試者對「鮮味」的感應門檻較高

meaning that they could barely taste it.

亦即他們很難真的嘗到鮮味

And those same patients were also ones who stated that food in general just wasn’t palatable to them anymore.

而這些同一群的病患也表示他們對一般的食物已無法感應味覺

As a result, they had suffered from loss of appetite and weight loss.

因此，他們身上出現食慾不佳的症狀且體重急速下降

Part of their problem, it turned out, was hyposalivation, or the inability to produce enough saliva.

這問題的一部份來自於缺涎症，也就是無法分泌充足的唾液

You have to produce saliva in order to taste anything,

要嘗味道你就必須分泌唾液

because food needs to be partially dissolved by saliva for our taste buds to register them.

因為食物有一部份得被唾液溶解，才能讓味蕾紀錄它的味道

And you know what actually stimulates saliva production? Foods with umami in it!

而你知道什麼東西能刺激唾液分泌嗎？正是有鮮味的食物！

So in a weird kind of catch-22, the patients needed to eat more umami in order to taste umami,

所以在《第 22 條軍規》這部小說中，病人必須吃更多的「鮮味」來提高他們的味覺

to get their appetites back.

促使他們恢復胃口

So the scientists prescribed a daily regime of konbu-cha, a tea made from kelp that’s rich in glutamate

於是科學家開了一劑日服處方，是用某種富含谷氨酸鹽的大型菌類所作，稱為冬菇茶

The tea began stimulating their umami receptors, which caused them to slowly increase saliva production.

這種茶開始刺激他們的鮮味器官，使他們漸漸恢復唾液分泌

And as they started to produce more saliva, they began to taste foods more strongly.

而當他們開始分泌較多的唾液，也更能感受食物的味道

Eventually, food became more palatable and they regained their appetite.

最終，他們能夠品嘗食物的美味，也恢復了胃口

Thank you for watching this particularly delicious episode of SciShow News.

謝謝您收看 SciShow News 這集特別美味的播出

If you want to help us share science with the world, you can become a supporting subscriber at Subbable.com/scishow.

如果你想要協助我們分享科學知識，可以透過 Subbable.com/scishow 來訂閱

And don’t forget to go to youtube.com/scishow and subscribe!

也別忘了在 YouTube 上訂閱我們的頻道！