大脑如何自我“清洁”

Just as our bodies produce waste every day—which is why we need to shower and use the toilet—our brains produce harmful waste proteins. But how can our brains “shower” themselves？

A 2013 study found the answer. Researchers at the US University of Rochester studied the brains of mice and discovered that they cleaned themselves while the mice slept. A kind of fluid in the brain， called cerebral spinal fluid （CSF）， was found to increase dramatically during sleep， washing away waste proteins that had been building up between brain cells in waking hours.

“This study shows that the brain has different functional states when asleep and when awake，” Maiken Nedergaard， the lead researcher， told NBC News. It also explains why we cant seem to think clearly after a sleepless night while a good nights sleep leaves us feeling sharp and refreshed.

Now a new study， published in Science， digs a little deeper into our brains self-cleaning procedure. Instead of mice， this time humans were the test subjects.

Researchers at Boston University， US， monitored the brain waves of 13 healthy adults who were sleeping， using accelerated fMRI （functional magnetic resonance imaging）， which is capable of recording faster changes inside the brain than a regular fMRI machine. They found that every 20 seconds， blood flowed out of the brain， making room for a large amount of CSF to come in and “clean”. This cycle coincided with the rhythm of the brains slow waves—an electrical activity that happens when were in deep sleep.

Its still unknown how these brain activities are connected. But the mere fact that they are connected is exciting enough， since it allows researchers to piece together possible new explanations for misunderstood diseases.

For example， slow-wave sleep has been proven to play a role in strengthening our memories. This may explain why people with Alzheimers often have fewer and weaker slow brainwaves. Based on this new study， there could be one more explanation for diseased brains： They are not clean.

Nedergaard， leader of the 2013 study， is also excited about the new findings. “Maybe the most important take-home message is that sleep is a serious thing，” she told Scientific American. “You really need to sleep to keep a healthy brain because it links electrical activity to a practical ‘housekeeping function.”

正如我們的身体每天都会产生废物——这也是我们需要洗澡、上厕所的原因——我们的大脑也会产生有害的废弃蛋白质。但是我们的大脑是如何“清洁”自己的呢？

一项2013年的研究找到了答案。美国罗切斯特大学的研究人员对老鼠的大脑进行了研究，发现老鼠在睡眠时会对大脑进行自我清洁。他们发现，老鼠的大脑内有种名为“脑脊液”的液体，在睡眠时会显著增加，“清洗”掉清醒时大脑细胞间堆积的废弃蛋白质。

“该研究表明，大脑在睡眠和清醒时的功能状态有所不同。”该研究首席研究员梅肯·内德加德在接受美国国家广播公司新闻频道采访时如此表示。研究也解释了失眠之后我们似乎无法清晰思考，而一夜安眠却让我们感到清醒振作的原因。

发表于《科学》期刊上的一项新研究进一步探究了我们大脑的自我清洁过程。这一次的实验对象不是老鼠，而是人类。

美国波士顿大学的研究人员通过增强性磁共振成像监测了13名健康成年人睡眠时的脑电波，和普通的功能性磁共振成像仪器相比，这种技术能够捕捉到脑内更快的变化。他们发现，每隔20秒血液会流出大脑，从而让大量脑脊液流入，进行“清洁”。这一循环与大脑慢波频率一致——这是一种我们进入深度睡眠才会发生的脑电活动。

这些大脑活动有何关联仍是未解之谜。但这些活动具有相关性的事实足以令人感到兴奋，因为这或许能让研究人员们拼凑出对于遭到误解的疾病的新解释。

比如，经过证实，慢波睡眠对于增强记忆起着关键作用。这或许解释了为何阿尔茨海默症患者的大脑慢波往往更少、更微弱。基于这项新研究，大脑的发病原因或许又多了一个解释：大脑不够“干净”。

2013年那项研究的首席研究员内德加德也对这些新发现感到兴奋。“或许最重要的关键信息就是睡眠很重要。”她在接受《科学美国人》杂志采访时表示。“你的确需要通过睡眠来保持大脑健康，因为这将大脑的‘清扫功能与脑电活动联系了起来。”

Word Study

sharp /?ɑ?p/ adj. 敏锐的;灵敏的;敏捷的

He kept a sharp lookout for any strangers.

flow /fl??/ v. 流;流动

Anxiety and sorrow can flow out of the body along with tears.

coincide /'k???n'sa?d/ v. 同时发生

The strike was timed to coincide with the party conference.

piece together  拼湊;拼合

Piece together the two seemingly separate events and youll understand them clearly.