我们每天都要睡觉，但是人为什么要睡觉呢？这个问题困扰了科学家几个世纪，最新的科学研究看起来就快找到这个问题的答案了。
Why do we sleep?
by Bryan Nelson
The average human spends 26 years of life sleeping. That's a lot of time, and for what? Interestingly, the question of why we sleep is one of the great mysteries of biology.
interestingly /ˈɪntrəstɪŋli/ adv. 有意思的是（由interesting加后缀-ly变成副词）
mystery /ˈmɪst(ə)ri/ n. 谜团
Most theorists believe that sleep is of particular importance to the health of the brain or the nervous system. After all, the effects of sleep deprivation usually take a mental toll, often in the form of memory loss, hallucinations（幻觉） or even seizures.
theorist /ˈθɪərɪst/ n. 理论家（由theory加上表示人的后缀-ist）
particular /pəˈtɪkjulə(r)/ adj. 特别的、特殊的（of particular importance意思是具有特别的重要性）
nervous /ˈnɜːvəs/ adj. 神经的、跟神经有关的
deprivation /ˌdeprɪˈveɪʃ(ə)n/ n. 剥夺、丧失（由deprive加后缀-ation变成名词）
take a toll 带来破坏、造成负面影响
mental /ˈment(ə)l/ adj. 精神的、思考的
form /fɔːm/ n. 形式
loss /lɒs/ n. 丢失
seizure /ˈsiːʒə(r)/ n. 惊厥、癫痫
In fact, a new study published in Nature Communications looked at how sleep deprivation affects the brain. If the brain is deprived of sleep for too long, the brain doesn't have time to repaired neuronal DNA damage that accumulates during waking hours.
affect /əˈfekt/ v. 影响
deprive /dɪˈpraɪv/ v. 剥夺
neuronal /njʊəˈrəunəl/ adj. 神经细胞的、神经元的
accumulate /əˈkjuːmjuleɪt/ v. 积累、积聚
A team of researchers turned to zebrafish（条纹热带鱼） for answers. They discovered that when the fish were awake, broken strands of DNA gathered together and chromosomes weren't active. When the fish were asleep, however, the DNA strands repaired themselves, and the chromosomes were more active. Their findings show that animals (and possibly humans, too) need sleep in order for single neurons to repair themselves.
researcher /rɪˈsɜːtʃə(r)/ n. 研究者（由research加上表示人的后缀-er）
turn to 转到
strand /strænd/ n. 一股、一缕（这里指DNA片段）
gather /ˈɡæðə(r)/ v. 聚集
chromosome /ˈkrəʊməsəʊm/ n. 染色体
active /ˈæktɪv/ adj. 活跃的
single /ˈsɪŋɡ(ə)l/ adj. 单个的
neuron /ˈnjʊərɒn/ n. 神经细胞、神经元
Breakthrough brain studies from the University of Wisconsin may offer even more answers. In short, we need to sleep to remember and to forget.
breakthrough /ˈbreɪkθruː/ n. 突破（由break和through组成）
Wisconsin /wɪˈskɒnsɪn/ n. 威斯康辛州（美国北部的州）
in short 简单来说
Research published in July 2016 and spearheaded by Giulio Tononi of the University of Wisconsin-Madison represents the best evidence yet of what happens when we sleep. Tononi's team took slices from the brains of mice before and after sleep. They found that synapses, or connections between neurons, were 18 percent smaller when sampled after a period of sleep. In other words, it seems that the connections between neurons in our brains are being trimmed or weakened while we snooze.
spearhead /ˈspɪəhed/ v. 带头做某事
represent /ˌreprɪˈzent/ v. 代表、意味着
the best yet 到目前为止最好的
evidence /ˈevɪd(ə)ns/ n. 证据
slice /slaɪs/ n. 切片
synapse /ˈsaɪnæps/ n. （这个词文中做了解释）
or /ɔː(r)/ conj. 也就是
connection /kəˈnekʃ(ə)n/ n. 连接、连接点（由connect加后缀-ion变成名词）
sample /ˈsɑːmp(ə)l/ v. 取样、采样
in other words 换句话说
trim /trɪm/ v. 修剪
weaken /ˈwiːk(ə)n/ v. 弱化、使变弱（由weak加后缀-en变成动词）
snooze /snuːz/ v. 打盹（这里指睡觉）
It may seem anti-intuitive to think about shrinking of the brain as a good thing, but it turns out that a slimmer brain has more room the following day to make new memories, according to a February 2017 study. Researchers hypothesize that sleeping allows us to "prune" our memories and fine-tune the lessons we've learned while awake. "Sleep is the price we pay for learning," explained Tononi.
anti- /ˈænti/ 前缀，意思是“反”
intuitive /ɪnˈtjuːɪtɪv/ adj. 直觉的
shrink /ʃrɪŋk/ v. 收缩、变小
turn out 结果是
slim /slɪm/ adj. 小的
hypothesize /haɪˈpɒθəsaɪz/ v. 提出假说
prune /pruːn/ v. 精简
fine-tune /faɪnˈtjuːn/ v. 细调、微调
price /praɪs/ n. 代价
The theory explains why we find it harder to concentrate and learn new information when we miss a night's sleep. It's because the brain has reached its capacity, so to speak; it needs to be pruned.
theory /ˈθɪəri/ n. 理论
concentrate /ˈkɒns(ə)ntreɪt/ v. 集中精神、集中注意力
capacity /kəˈpæsəti/ n. 容量
so to speak 可以这么说、差不多这样
If Tononi's research makes you frightened to sleep for fear of having your experiences trimmed off, not to worry. The research also found that some synapses were protected from the trimming process, always remaining robust. These areas are probably where the most important memories are being stored. "You keep what matters," reassured Tononi.
frightened /ˈfraɪt(ə)nd/ adj. 吓坏的、害怕的
process /ˈprəʊses/ n. 过程
robust /rəʊˈbʌst/ adj. 健壮的、结实的
store /stɔː(r)/ v. 储存
matter /ˈmætə(r)/ v. 要紧、是重要的
reassure /ˌriːəˈʃʊə(r)/ v. 宽慰、使安心
（如果您使用的是火狐浏览器，可能会发现某些行的最后一个单词被分成两半了，这是简书系统的Bug，换成Chrome或其他浏览器就能正常显示了。）
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