研究称上班摸鱼是大脑在排毒

近日，发表在《当代生物学》（Current Biology）期刊上的一项研究表明，在一天中人越努力思考，大脑前额叶皮层中「谷氨酸」的含量积累得越多。而谷氨酸积累过多会破坏大脑功能，让人觉得疲惫不堪、难以集中精神。

想要消除这种「毒素」？那就停下来打个盹、摸摸鱼，休息一下吧！

无注释原文：

Why thinking hard makes you tired

From: EurekAlert!

11-AUG-2022

It’s no surprise that hard physical labor wears you out, but what about hard mental labor? Sitting around thinking hard for hours makes one feel worn out, too. Now, researchers have new evidence to explain why this is, and, based on their findings, the reason you feel mentally exhausted (as opposed to drowsy) from intense thinking isn’t all in your head.

Their studies, reported in Current Biology on August 11, show that when intense cognitive work is prolonged for several hours, it causes potentially toxic byproducts to build up in the part of the brain known as the prefrontal cortex. This in turn alters your control over decisions, so you shift toward low-cost actions requiring no effort or waiting as cognitive fatigue sets in, the researchers explain.  

“Influential theories suggested that fatigue is a sort of illusion cooked up by the brain to make us stop whatever we are doing and turn to a more gratifying activity,” says Mathias Pessiglione of Pitié-Salpêtrière University in Paris, France. “But our findings show that cognitive work results in a true functional alteration—accumulation of noxious substances—so fatigue would indeed be a signal that makes us stop working but for a different purpose: to preserve the integrity of brain functioning.”

Pessiglione and colleagues including first author of the study Antonius Wiehler wanted to understand what mental fatigue really is. While machines can compute continuously, the brain can’t. They wanted to find out why. They suspected the reason had to do with the need to recycle potentially toxic substances that arise from neural activity.

To look for evidence of this, they used magnetic resonance spectroscopy (MRS) to monitor brain chemistry over the course of a workday. They looked at two groups of people: those who needed to think hard and those who had relatively easier cognitive tasks.

They saw signs of fatigue, including reduced pupil dilation, only in the group doing hard work. Those in that group also showed in their choices a shift toward options proposing rewards at short delay with little effort. Critically, they also had higher levels of glutamate in synapses of the brain’s prefrontal cortex. Together with earlier evidence, the authors say it supports the notion that glutamate accumulation makes further activation of the prefrontal cortex more costly, such that cognitive control is more difficult after a mentally tough workday.

So, is there some way around this limitation of our brain’s ability to think hard?

“I would employ good old recipes: rest and sleep! There is good evidence that glutamate is eliminated from synapses during sleep,” Pessiglione said.

There may be other practical implications. For example, the researchers say, monitoring of prefrontal metabolites could help to detect severe mental fatigue. Such an ability may help adjust work agendas to avoid burnout. He also advises people to avoid making important decisions when they’re tired.

In future studies, they hope to learn why the prefrontal cortex seems especially susceptible to glutamate accumulation and fatigue. They’re also curious to learn whether the same markers of fatigue in the brain may predict recovery from health conditions, such as depression or cancer.

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注：中文文本为机器翻译仅供参考，并非一一对应

含注释全文：

Why thinking hard makes you tired

From: EurekAlert!

11-AUG-2022

It’s no surprise that hard physical labor wears you out, but what about hard mental labor? Sitting around thinking hard for hours makes one feel worn out, too. Now, researchers have new evidence to explain why this is, and, based on their findings, the reason you feel mentally exhausted (as opposed to drowsy) from intense thinking isn’t all in your head.

重体力劳动会让你筋疲力尽，这并不奇怪，但是重脑力劳动呢？坐在那里努力思考几个小时也会让人感到筋疲力尽。现在，研究人员有了新的证据来解释为什么会这样。根据他们的发现，你因为紧张的思考而感到精神疲惫（而不是昏昏欲睡）的原因并不全在于大脑。

表示“使（某人）筋疲力尽”，英文解释为“to make someone extremely tired”举个🌰：

Walking around a museum all day really wears you out.

整天在博物馆里走来走去，真的让人筋疲力尽。

drowsy /ˈdraʊ.zi/ 表示“睡意朦肬的，半梦半醒的，似睡非睡的”，英文解释为“being in a state between sleeping and being awake”举个🌰：

The room is so warm it's making me feel drowsy.

房间非常暖和，让我有些昏昏欲睡。

🎬电影《副作用》（Side Effects）中的台词提到：After a few minutes, you'll probably get drowsy and fall asleep. 再过几分钟你就会昏昏入睡的。

Their studies, reported in Current Biology on August 11, show that when intense cognitive work is prolonged for several hours, it causes potentially toxic byproducts to build up in the part of the brain known as the prefrontal cortex. This in turn alters your control over decisions, so you shift toward low-cost actions requiring no effort or waiting as cognitive fatigue sets in, the researchers explain.

表示“（不好的事）到来，开始（而且可能会持续）”，英文解释为“When something unpleasant sets in, it begins and seems likely to continue in a serious way.”举个🌰：

This rain looks as if it has set in for the rest of the day.

看来今天雨不会停。

🎬电影《人类之子》（Children of Men）中的台词提到：As the sound of the playgrounds faded, the despair set in. 游乐场的声音逐渐淡去，接着是绝望。

“Influential theories suggested that fatigue is a sort of illusion cooked up by the brain to make us stop whatever we are doing and turn to a more gratifying activity,” says Mathias Pessiglione of Pitié-Salpêtrière University in Paris, France. “But our findings show that cognitive work results in a true functional alteration—accumulation of noxious substances—so fatigue would indeed be a signal that makes us stop working but for a different purpose: to preserve the integrity of brain functioning.”

cook /kʊk/ 表示“编造，捏造”，英文解释为“to invent a story, plan, etc., usually dishonestly”举个🌰：

She cooked up some weird scheme that was going to earn her a fortune.

她想出了个能使自己发财的怪点子。

gratifying /ˈɡræt.ɪ.faɪ.ɪŋ/ 表示“心满意足的”，英文解释为“pleasing and satisfying”举个🌰：

It must be very gratifying to see all your children grown up and happy.

看到孩子们都长大成人、生活幸福，你一定感到心满意足吧。

accumulation /əˌkjuː.mjəˈleɪ.ʃən/ 表示“积累；积聚；积攒”，英文解释为“an amount of something that has been collected”举个🌰：

Despite this accumulation of evidence, the government persisted in doing nothing.

尽管种种迹象不断出现，政府仍然坚持不采取任何行动。

Pessiglione and colleagues including first author of the study Antonius Wiehler wanted to understand what mental fatigue really is. While machines can compute continuously, the brain can’t. They wanted to find out why. They suspected the reason had to do with the need to recycle potentially toxic substances that arise from neural activity.

佩西格隆和他的同事，包括这项研究的第一作者安东尼尔斯·维勒（Antonius Wiehler），想了解精神疲劳（mental fatigue）到底是什么。虽然机器可以持续计算，但大脑不能。他们想找出原因。他们怀疑这与神经活动产生的潜在有害物质需要回收有关。

To look for evidence of this, they used magnetic resonance spectroscopy (MRS) to monitor brain chemistry over the course of a workday. They looked at two groups of people: those who needed to think hard and those who had relatively easier cognitive tasks.

为了寻找这方面的证据，他们使用磁共振波谱（MRS）监测一个工作日内的脑化学变化。他们观察了两组人：需要努力思考的人和认知任务相对容易的人。

spectroscopy /spekˈtrɒs.kə.pi/ 表示“光谱学”，英文解释为“the study of the way matter absorbs or sends out light and other radiation (= energy from light or heat that you cannot see) ”

They saw signs of fatigue, including reduced pupil dilation, only in the group doing hard work. Those in that group also showed in their choices a shift toward options proposing rewards at short delay with little effort. Critically, they also had higher levels of glutamate in synapses of the brain’s prefrontal cortex. Together with earlier evidence, the authors say it supports the notion that glutamate accumulation makes further activation of the prefrontal cortex more costly, such that cognitive control is more difficult after a mentally tough workday.

他们发现了疲劳的迹象，包括瞳孔扩张减少，但这只发生在努力工作的那组人身上。该组人在决策中也表现出向在短时间就能轻而易举获得奖励的选项转变。关键的是，他们大脑前额叶皮层突触中的谷氨酸（glutamate）水平也较高。作者说，结合早期的证据，这支持了谷氨酸的积累会使前额叶皮层进一步激活的成本更高的观点，因此在精神紧张的一天之后，认知控制会更加困难。

pupil /ˈpjuː.pəl/ 表示“学生，（尤指）小学生”，此次熟词僻义，表示“瞳孔”，英文解释为“the circular black area in the centre of an eye, through which light enters”举个🌰：

Pupils contract in bright light, and dilate in darkness.

瞳孔在明亮的光线下会收缩，在黑暗中会扩大。

dilation /daɪˈleɪ.ʃən/ 表示“扩张”，英文解释为“the state of being larger or more open than usual”

synapse /ˈsaɪ.næps/ 表示“（神经元的）突触”，英文解释为“the point at which electrical signals move from one nerve cell to another”

So, is there some way around this limitation of our brain’s ability to think hard?

那么，有没有办法克服我们大脑努力思考能力的限制？

“I would employ good old recipes: rest and sleep! There is good evidence that glutamate is eliminated from synapses during sleep,” Pessiglione said.

佩西格隆说：“我会采用很好的老方法：休息和睡眠！有很好的证据表明，谷氨酸在睡眠过程中会从突触中消除。”

There may be other practical implications. For example, the researchers say, monitoring of prefrontal metabolites could help to detect severe mental fatigue. Such an ability may help adjust work agendas to avoid burnout. He also advises people to avoid making important decisions when they’re tired.

可能还有其他实际意义。例如，研究人员说，监测前额代谢物有助于发现严重的精神疲劳。这种能力可能有助于调整工作议程，以避免过度劳累。他还建议人们在疲劳时避免做出重要决定。

metabolite /məˈtæb.ə.laɪt/ 表示“代谢物”，英文解释为“any substance involved in metabolism (= the chemical processes in the body needed for life)”如：metabolite levels 代谢物水平。

In future studies, they hope to learn why the prefrontal cortex seems especially susceptible to glutamate accumulation and fatigue. They’re also curious to learn whether the same markers of fatigue in the brain may predict recovery from health conditions, such as depression or cancer.

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