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.”

正如我們的身體每天都會(huì)產(chǎn)生廢物——這也是我們需要洗澡、上廁所的原因——我們的大腦也會(huì)產(chǎn)生有害的廢棄蛋白質(zhì)。但是我們的大腦是如何“清潔”自己的呢？

一項(xiàng)2013年的研究找到了答案。美國(guó)羅切斯特大學(xué)的研究人員對(duì)老鼠的大腦進(jìn)行了研究，發(fā)現(xiàn)老鼠在睡眠時(shí)會(huì)對(duì)大腦進(jìn)行自我清潔。他們發(fā)現(xiàn)，老鼠的大腦內(nèi)有種名為“腦脊液”的液體，在睡眠時(shí)會(huì)顯著增加，“清洗”掉清醒時(shí)大腦細(xì)胞間堆積的廢棄蛋白質(zhì)。

“該研究表明，大腦在睡眠和清醒時(shí)的功能狀態(tài)有所不同?！痹撗芯渴紫芯繂T梅肯·內(nèi)德加德在接受美國(guó)國(guó)家廣播公司新聞?lì)l道采訪(fǎng)時(shí)如此表示。研究也解釋了失眠之后我們似乎無(wú)法清晰思考，而一夜安眠卻讓我們感到清醒振作的原因。

發(fā)表于《科學(xué)》期刊上的一項(xiàng)新研究進(jìn)一步探究了我們大腦的自我清潔過(guò)程。這一次的實(shí)驗(yàn)對(duì)象不是老鼠，而是人類(lèi)。

美國(guó)波士頓大學(xué)的研究人員通過(guò)增強(qiáng)性磁共振成像監(jiān)測(cè)了13名健康成年人睡眠時(shí)的腦電波，和普通的功能性磁共振成像儀器相比，這種技術(shù)能夠捕捉到腦內(nèi)更快的變化。他們發(fā)現(xiàn)，每隔20秒血液會(huì)流出大腦，從而讓大量腦脊液流入，進(jìn)行“清潔”。這一循環(huán)與大腦慢波頻率一致——這是一種我們進(jìn)入深度睡眠才會(huì)發(fā)生的腦電活動(dòng)。

這些大腦活動(dòng)有何關(guān)聯(lián)仍是未解之謎。但這些活動(dòng)具有相關(guān)性的事實(shí)足以令人感到興奮，因?yàn)檫@或許能讓研究人員們拼湊出對(duì)于遭到誤解的疾病的新解釋。

比如，經(jīng)過(guò)證實(shí)，慢波睡眠對(duì)于增強(qiáng)記憶起著關(guān)鍵作用。這或許解釋了為何阿爾茨海默癥患者的大腦慢波往往更少、更微弱?；谶@項(xiàng)新研究，大腦的發(fā)病原因或許又多了一個(gè)解釋?zhuān)捍竽X不夠“干凈”。

2013年那項(xiàng)研究的首席研究員內(nèi)德加德也對(duì)這些新發(fā)現(xiàn)感到興奮。“或許最重要的關(guān)鍵信息就是睡眠很重要?！彼诮邮堋犊茖W(xué)美國(guó)人》雜志采訪(fǎng)時(shí)表示?！澳愕拇_需要通過(guò)睡眠來(lái)保持大腦健康，因?yàn)檫@將大腦的‘清掃功能與腦電活動(dòng)聯(lián)系了起來(lái)?！?/p>

Word Study

sharp /?ɑ?p/ adj. 敏銳的;靈敏的;敏捷的

He kept a sharp lookout for any strangers.

flow /fl??/ v. 流;流動(dòng)

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

coincide /'k???n'sa?d/ v. 同時(shí)發(fā)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.