A
We take showers and use the toilet every day to get rid of bodily waste. Our brains also need to take a bath every day. How can they do it?
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 (液体) in the brain
called cerebral spinal fluid (CSF, 脑脊液), was found to increase dramatically (显著地) 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 can’t seem to think clearly after a sleepless night while a good night’s sleep leaves us feeling sharp and refreshed.
Now a new study, published on Oct. 31 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 brainwaves of 13 healthy adults who were sleeping, using accelerated FMRI (核磁共振成像), 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 (与.一致) the rhythm of the brain’s slow waves—an electrical activity that happens when we’re in a deep sleep.
It’s 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 (拼凑出) 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 Alzheimer (阿尔茨海默病) 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 activities to a practical ‘housekeeping’ function.”
1. What did the researchers find when they studied the brains of mice?
A. CSF in their brains decreased when the mice slept.
B. More waste proteins were produced in their brains during sleep.
C. CSF carried away waste proteins in their brains during sleep.
D. The more CSF was in their brains, the fewer proteins were there.
2. What did the researchers discover when they monitored human brainwaves?
A. It took 20 seconds for CSF to clean brains.
B. Brains were “cleaned” when blood flowed out.
C. The rhythm of the brain was slower than that of CSF.
D. The brains worked more slowly when asleep.
3. What are the last three paragraphs mainly about?
A. The significance of the research.
B. The features of slow-wave sleep.
C. The importance of having a good sleep.
D. The connections between these brain activities.
【答案】1. C 2. B 3. A
【解析】
本文是一篇说明文，我们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。但是我们的大脑又是如何“清洁”自己的呢？研究发现我们是通过脑脊液清理大脑内的垃圾的，这个发现具有重要的意义。
【1题详解】
细节理解题。根据第二段中的“A kind of fluid (液体) in the brain, called cerebral spinal fluid (CSF, 脑脊液), was found to increase dramatically (显著地) during sleep, washing away waste proteins that had been building up between brain cells in waking hours.”可知，研究人员发现老鼠大脑中一种叫做脑脊髓液的液体在睡眠中显著增加，清除了清醒时在脑细胞间积聚的废物蛋白质，故C项正确。
【2题详解】
细节理解题。根据第五段中的“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”.”可知，研究人员发现，每20秒，血液就从大脑中流出，为大量脑脊液进入大脑和“清洗”留出空间，故B项正确。
【3题详解】
主旨大意题。根据后三段内容，特别是根据倒数第三段中的“it allows researchers to piece together (拼凑出) possible new explanations for misunderstood diseases.”，倒数第二段中的“Based on this new study, there could be one more explanation for diseased brains: They are not clean.”及最后一段中的“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,”” 可知，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、表明患阿尔兹海默病的人的大脑并不干净、“或许最重要的关键信息就是睡眠很重要，所以最后三段主要讲的是这一研究的意义。故A项正确。
