托福 阅读背景知识之褪黑素
【托福阅读备考】托福阅读背景知识 头发的作用
【托福阅读备考】托福阅读背景知识头发的作用头发，枯了不痒，剪了不疼，那头发是做什么用的?是为了美观?还是为了御寒?这些回答都不全面，下面，就请跟着小编进入今天的托福阅读材料，来详细了解一下我们的头发。
A human hair consists mainly of a protein called Keratin. It also containssome moisture and the trace metals and minerals found in the rest of thebody.人类的头发主要由一种叫角朊的蛋白质组成，并含有水分及在身体其他部分也可找到的微量金属和矿物质。
● The only living part of hair is underneath the scalp--when the hair hadgrown through the scalp it is dead tissue.头发唯一有生命的部分是在头皮下面，当它长出头皮时便成为无生命组织。
● Hair’s natural shine is supplied by its own conditioner, sebum, an oilcomposed of waxes and fats and also containing a natural antiseptic that helpsfight infection. Too much sebum results in greasy hair and conversely, toolittle sebum makes dry hair.头发的自然光泽来自它自身的护发素：油脂，它含有蜡和脂肪，还含有抗感染的自然抗菌剂。
油脂含量过多会导致油性发质，相反，油脂含量过少则会导致干性发质。
● Hair grows about 12 mm per month. If a person never has his hair cut, itwould grow to a length of about 108 cm before falling out. Hair grows faster inthe summer and during sleep. A single strand lives for up to seven years.头发每个月可长12毫米，如果一个人从不剪发，头发会长至108厘米才开始脱落。
托福阅读真题第236篇Sleep
托福阅读真题第236篇Sleep托福阅读真题第236篇SleepSleepParagraph 1: Why do we sleep? It can be dangerous to lose awareness of the external world. If nothing else, sleep might seem to take away from time that could be spent on productive, or even necessary, activities. But people cannot override indefinitely the desire to sleep; the body shuts down whether we like it or not. There are three general explanations that describe the adaptiveness of sleep: restoration, circadian cycles, and facilitation of learning.Paragraph 2: The restoration theory of sleep emphasizes that the brain and body need to rest and that sleep allows the body to repair itself. Indeed, growth hormone's released during deep sleep, and one of its functions is to facilitate repair of damaged tissue. Additional evidence that sleep is a time of restoration is that people who have engaged in vigorous physical activity, such as running marathons, seem to sleep longer. But people sleep even if they spend the day being physically inactive. In addition, it appears that sleep allows the brain to strengthen the body's ability to fight disease.1. According to paragraph 2, all of the following are considered to be evidence that sleep is needed for the body to repair itself EXCEPT:A. The body’s resistance to disease is strengthened through sleep.B. Body tissues are restored by the release of hormones during sleep.C. The longer people sleep, the more activity occurs.D. Sleep occurs whether or not physical activity has taken place.Paragraph 3: Numerous laboratory studies have examined the effects of sleep deprivation on physical and cognitive performance. Surprisingly, most studies find that two or three days of deprivation have little effect on strength, athletic ability, or cognitive performance on complex tasks. Performing boring or ordinary tasks when sleep deprived, however, is nearly impossible. A brain-imaging study of sleep-deprived people found increased activation of the prefrontal cortex, suggesting that some brain regions may compensate for the effects of deprivation. Over long periods, however, sleep deprivation eventually causes problems with mood and cognitive performance. Indeed, studies using rats have found that extended sleep deprivation compromises the immune system and leads to death. Interestingly, sleep deprivation might serve one very useful purpose, which is helping people overcome depression. Consistent evidence has emerged over the past decade demonstrating that depriving depressed people of sleep sometimes alleviates their depression. This effect appears to occur because sleep deprivation leads to increased activation of serotonin receptors, which combat depression.2. Why does the author say “Performing boring or ordina ry tasks when sleep deprived, however, is nearly impossible”?A. To identify a type of task in which being sleep-deprived for a few days actually does affect physical and cognitive performanceB. To suggest that simple tasks are easier to perform than complex tasks after sleep deprivationC. To indicate an important finding of a brain-imaging studyon the effects of sleep deprivation on the prefrontal cortexD. To suggest that physical acts are preformed more easily than cognitive acts after sleep deprivation3. According to paragraph 3, what was one unexpected finding reported by studies investigating sleep deprivation?A. Sleep deprivation helps people perform better on complex tasks.B. Sleep deprivation of a few days’ duration does not significantly weaken performance on challenging tasks.C. Sleep deprivation is more common in people who are physically inactive than it is in active people.D. Sleep deprivation can sometimes temporarily improve physical abilty.4. Which of the following can be inferred from the discussion about sleep deprivation in paragraph 3？A. Short-term sleep deprivation has a negative impact on athletic performance.B. Short-term sleep deprivation severely harms the immune system.C. Sleep deprivation can have both positive and negative effects.D. Sleep deprivation improves cognitive development by activating serotonin receptors.Paragraph 4: The circadian rhythm theory of sleep proposes that sleep has evolved to keep animals quiet and inactive during times of the day when there is greatest danger, which for most is when it is dark. Physiological and brain processes are regulated into regular patterns known as circadian rhythms (“circadian” roughly translates to “about a day”). Body temperature, hormone levels, and sleep-wake cycles are all examples ofcircadian rhythms, which operate like biological clocks. These circadian rhythms are themselves controlled by cycles of light and dark, although animals continue to show these rhythms when light cues are removed.5. According to paragraph 4, which of the following is NOT true of the circadian rhythms of animals?A. Circadian rhythms regulate physiological processes such as body temperature, hormone levels, and sleep-wake cycles of animals.B. Animals that are kept in darkness will stop following circadian rhythms.C. The daily periods of light and dark regulate the circadian rhythms of animals.D. Sleep occurs during the part of the circadian cycle in which an active animal would be in the most danger.Paragraph 5: According to the circadian rhythm theory, animals need only so much time in the day to accomplish the necessities of survival, and it is adaptive to spend the remainder of the time inactive, preferably hidden away. Accordingly, the amount an animal sleeps depends on how much time it needs to obtain food, how easily it can hide, and how vulnerable it is to attack. Small animals sleep a great deal, whereas large animals vulnerable to attack, such as cows and deer, sleep little. Large animals that are not vulnerable, such as lions, also sleep a great deal.6. According to the circadian rhythm theory described in paragraph 5, which of the following does NOT determine the amount of time an animal sleeps?A. How easily the animal can hide from attackersB. How much energy the animal’s food providesC. How likely it is that the animal will be attacked when it is activeD. The amount of time the animal needs to find foodParagraph 6: It has been proposed that sleep may be important because it is involved in the strengthening of nerve cell connections that serve as the basis of learning. The general idea is that circuits that have been wired together during the waking period are consolidated, or strengthened, during sleep. Robert Stickgold and colleagues conducted a study in which they required participants to learn a complex visual-discrimination task. They found that participants improved at the task only if they had slept for at least six hours following training. Periods of sleep with increased brain activity as well as periods of sleep with reduced brain activity appeared to be important for learning to take place. The researchers argued that learning the task required nerve cell changes that normally occur only during sleep. Although learning certainly can take place in the absence of sleep, sleep seems to be an efficient time for the consolidation of learning. Infants and the very young, who learn an incredible amount in a few short years, sleep the most and also spend the most time in periods of sleep with higher brain activity.7. According to paragraph 6, what was a major finding of the study conducted by Robert Stickgold and his colleagues?A. Most learning takes place during deep sleep.B. Information and skills acquired during the day are reinforced during sleep.C. Visual discrimination tasks cannot be learned without sleeping afterward.D. At least six hours of sleep before performing a task is necessary for learning to occur.8. In paragraph 6, why does the author mention that infants and very young people sleep the most?A. To argue against the findings of the study conducted by Robert Stickgold and his colleaguesB. To suggest that learning is not possible if infants and young people are deprived of sleepC. To support the claim that sleep is critical to learning and reinforces it in important waysD. To indicate that the brain circuits responsible for learning are more active in infants and young people than they are in adultsParagraph 4: The circadian rhythm theory of sleep proposes that sleep has evolved to keep animals quiet and inactive during times of the day when there is greatest danger, which for most is when itis dark. Physiological and brain processes are regulated into regular patterns known as circadian rhythms (“circadian” roughly translates to “about a day”). Bod y temperature, hormone levels, and sleep-wake cycles are all examples of circadian rhythms, which operate like biological clocks. ■These circadian rhythms are themselves controlled by cycles of light and dark, although animals continue to show these rhythms when light cues are removed.Paragraph 5: ■According to the circadian rhythm theory, animals need only so much time in the day to accomplish the necessities of survival, and it is adaptive to spend the remainder of the time inactive, preferably hidden aw ay. ■Accordingly, the amount an animal sleeps depends on how much time it needs to obtain food, how easily it can hide, and how vulnerable it is to attack. Small animals sleep a great deal, whereas large animals vulnerable to attack, such as cows and deer, sleep little. ■Largeanimals that are not vulnerable, such as lions, also sleep a great deal.9. Look at the four squares [■] that indicate where the following sentence could be added to the passage. Where would the sentence best fit?But how do biological clocks affect the amount of time an animal sleeps each day?10. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selected THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.Several theories have been proposed to explain why sleep is important.Answer ChoicesA. Sleep may be necessary to increase the body’s energy for use in physical activity, which in turn may speed up the process of tissue restoration.B. Sleep may help repair damage to the body, although evidence suggests that only a long-term lack of sleep would cause a decline in physical health and cognitive functioning.C. Sleep may control the development of daily rhythms that regulate basic physiological properties, such as body temperatures and hormone levels.D. The function of sleep cycles in animals may be to allow them to minimize activity during periods of high risk.E. Sleep may influence brain development by increasing the number of neuronal connections, which would explain why infants demonstrate higher brain activity than adults do.F. Sleep may enable certain physiological changes that normally occur only during sleep to support and strengthen the process of learning.答案TF236-Sleep（答案文章最后）托福阅读真题第236篇Sleep。
考研英语阅读理解外刊原文阅读
Drinking Milk Before Bed: Is It a Good Idea?睡前喝牛奶究竟好不好？A handful of small animal and human studies demonstrate that consuming dairy products like milk and cheese before bed may help some people have a more restful night’s sleep, though the reason why remains unclear.一些针对小动物和人类的研究表明，睡前饮用牛奶或奶酪等乳制品或许能给人们带来更宁静的睡眠，但尚不清楚其中的缘由。
Most experts agree that milk’s sleep-promoting potential is likely related to specific chemical compounds or the psychological effects of having a soothing bedtime routine — or perhaps a combination of the two.大多数专家都认为，牛奶之所以能够促进睡眠可能与特定的化合物有关，也可能与睡前习惯带来的心理效应有关——或者两者兼而有之。
Certain compounds in milk — specifically tryptophan and melatonin — may help you fall asleep.牛奶中的某些化合物（特别是色氨酸和褪黑素）或许有助于入睡。
Tryptophan is an amino acid found in a variety of protein-containing foods. It plays an important role in the production of the neurotransmitter known as serotonin .色氨酸是一种存在于各种含蛋白质食物中的氨基酸。
TOEFL英语阅读分类词汇（1）
TOEFL英语阅读分类词汇（1）TOEFL英语阅读分类词汇精选(1)词汇对于英语学习来说非常重要，无论是TOEFL还是GRE，词汇都相当重要，在做阅读理解时，你会深刻的体会到。
同样GRE的词汇测试也是让我们非常吃惊的，许多僻词，连老外都不晓得，可是我们记住了。
对我而言，分类比较记忆词汇相当有效，不妨一试，我们将陆续为大家介绍TOEFL阅读分类词汇。
生物类：chlorophyll 叶绿素amino acids 氨基酸protein 蛋白质nitrogen 氮photosynthetic（adj.） photosynthesis（n.）光合作用botany 植物学botanist 植物学家lichen 地衣，苔藓fungus（pl. fungi）菌类algae（pl. alga）海藻bacterium（pl.bacteria）细菌organism 有机物rodent 啮齿类动物primate 灵长类动物mammal 哺乳类动物reptile 爬行类动物predator 捕食者prey 被捕食者acquatic 水生的artery 动脉vein 静脉fingernail 指甲scale 鳞片claw 爪子horn 角nourish 滋养，供给……营养clam 蚌crab 虾beaver 狸pond 池塘puddle 水坑snail 蜗牛shrimp 虾hormone 荷尔蒙intestine 肠corn 谷物squash 南瓜bean 豆类植物nectar 花蜜pollen 花粉hive 蜂巢moss 苔藓hibernate 冬眠penguin 企鹅reef 礁coral 珊瑚beak 鸟嘴enzymes 酵母larvae 幼虫tadpole 蝌蚪caterpillar 毛虫grasshopper 蚱蜢toad 蟾蜍herbicide 除草剂secretion（n.） secrete（v.）分泌pancreas 胰腺odor气味（还有aroma fragrance scent smell大概意思相同，都有“气味”的意思，幸亏不是GRE，hehe）roe 鱼卵caviar 鱼子酱raccoon 浣熊gland 腺体cricket 蟋蟀2、文学，艺术gossip 闲谈rumor 传闻，谣言comic a.使人发笑的a comic song b.喜剧的a comic operapoetic 诗意的，诗。
褪黑素与失眠的相关知识总结
褪黑素与失眠的相关知识总结Background：褪黑素，由松果体分泌，属吲哚类激素。
人类从出生3个月开始分泌褪黑素，6岁达到高峰期，12岁降至成人水平，以后随年龄增长分泌逐渐减少，至45岁降至原有水平一半。
研究发现，褪黑素能够治疗失眠，有关文献报告，有证据证明4周内短期治疗睡眠没有效果，3个月内治疗过程中无副作用，不过，褪黑素可以短期有效治疗慢波推迟的失眠。
褪黑素治疗或者抵抗失眠的药物呢？Abstract：褪黑素具有广泛的生物学效应，对生殖、内分泌系统功能有明显的影响，近年来它还对人体的衰老，免疫及生物节律具有重要调节作用。
1、生殖系统的影响：实验发现，摘除大鼠松果体后，性腺重量增加。
患松果体非实质性肿瘤的男孩，出现性早熟。
向大鼠下丘脑或脑干注射褪黑素，可降低LH和FSH的含量，并阻断排卵。
上述观察和实验表明，褪黑素可抑制下丘脑GhRH的释放，进而影响垂体促性腺激素的合成和释放，对性腺发育起抑制作用。
2、对甲状腺、肾上腺的影响：实验发现，切除大鼠松果体后，甲状腺和肾上腺明显增大，甲状腺摄碘作用增强，碘更新速率加速。
若给雌性田鼠每天注射褪黑素25ug可使血浆T4和游离甲状腺素指数下降，促甲状腺水平激素明显降低。
这些观察结果说明松果体激素具有抑制下丘脑-垂体-甲状腺轴和肾上腺皮质功能的作用。
3、调节衰老过程：实验表明MT(褪黑素)或进行松果体移植，可在一定程度上延缓衰老，并降低老年病的发生。
4、调节生物节律：人体许多生理功能都有日周期节律，如体温、ACTH分泌量及血细胞计数。
研究指出，下丘脑视交叉上核可能是控制昼夜节律的关键部位。
视交叉上核的神经元有MT受体。
MT可作为一个内源性因子作用于视交叉上核。
有研究表明，人和哺乳动物的MT昼夜分泌节律与睡眠的昼夜时相完全一致，生理剂量的MT具有促睡眠的作用，有人推测MT可能是睡眠的促发因子。
Purpose：从中医到西方经典理论，失眠相关因素有肝脏、MT（褪黑素）、γ-氨基丁酸（GABA）、色氨酸、5-HT（五羟色胺）、VB6。
TOEFL新托福阅读背景知识汇总
TOEFL新托福阅读背景知识汇总TOEFL新托福阅读背景学问汇总为了让大家更好的预备托福考试，我给大家整理新托福阅读背景学问汇总，下面我就和大家共享，来观赏一下吧。
新托福阅读背景学问：现代派文学的兴起两次世界大战之间从第一次世界大战到其次次世界大战，是US文学的其次次富强时期。
20年月，各种流派相继消失，表现了高度进展的资本主义社会的种.种冲突和精神世界方面的问题。
30年月基本上是左翼文学占主导地位，从30年月后期起，文学界分化成各个流派，又消失了纷坛多样的局面。
总的来说，现代派文学与左翼文学是这个时期两股最大的文学思潮。
从这个时期起，US文学开头发生世界性的影响。
1930年后，US作家间续得到诺贝尔文学奖金。
现代派文学的兴起20世纪初，US的经济有了很大进展。
垄断资本进一步集中，大城市人口密集，工农运动规模越来越大。
社会面貌与人的精神面貌，已非19世纪传统现实主义手法与惠特曼式的风格所能精确反映。
大战前的最初10年为孕育新的风格、新的流派作了预备。
欧洲的现代派文艺不断介绍到US。
19世纪下半期US的诗歌处于过渡阶段，继惠特曼后只消失了一个重要诗人艾米莉·狄更生。
她一反浮夸的浪漫主义诗风，以不规章的韵律、奇怪的对比和自由的联想，打开了通向US现代诗的道路。
1912年，《诗刊》在芝加哥创办，标志着现代派文艺的开头。
《诗刊》的头3卷里，消失了庞德(1885-1973)、韦·林赛(1879-1931)、艾·洛威尔(1874-1925)、威·卡·威廉斯(1883-1963)、桑德堡(1878-1967)、沃·斯蒂文斯(1879-1955)、艾·李·马斯特斯(1868-1950)、玛·莫尔(1887-1972)等人的作品。
这些人后来都成为US有成就的诗人。
其中有意象主义者，有接近劳动人民的芝加哥诗派，有20世纪的田园诗人，有新的乡土主义者，有抽象哲理派诗人。
文献翻译
褪黑素，一个被低估的具有巨大潜力的农业应用的天然物质摘要：褪黑素（MEL）被认为是唯一存在脊椎动物中的一种神经递质，直到在其他生物体包括植物体被检测发现。
尽管有关褪黑素在植物体内功能的文章大量发表，但是对于褪黑素功能这方面的知识仍然很缺乏。
大量实验证据表明，植物体内的褪黑素是作为一种抗氧化剂和生长促进剂来行使功能的。
这种化合物是一个独立的植物生长调节剂，它可能介导的其他植物生长调节剂的活动。
由于其抗氧化的性质，褪黑素可以稳定细胞的氧化还原态和防止植物组织在逆境条件下活性氧和活性氮的积累。
一些研究人员认为，褪黑素可以提高植物对不同污染物的植物修复效率。
在本文中，我们发现外源性褪黑素应用到种子中可能是一个很好的生物刺激物，它不仅可以提高种子萌发，幼苗发育和植物生长，而且能在胁迫条件下提高作物生产。
我们也相信这种化合物能增加食物的品质（功能性食品方面）和改善人类健康。
由于褪黑素是廉价的，并且对动物和人类是一种安全的生物刺激物，所以它在农业中的应用是一种优秀的，可行的和具有成本效益的方法。
褪黑素（MEL）是1958年由亚伦·勒纳和他的同事从牛的松果体分离得到的，并对其结构进行了鉴定为N-乙酰基-5-甲氧基色胺。
起初，褪黑素被认为只发生在动物身上，但在Science （1991）的一篇文章改变了这种看法，因为作者在Lingulodiniumpolyedrum光合藻（现名Gonyaulaxpolyedra）中发现了这种物质。
这个信息激发了科学家在其他自养生物，包括高等植物中搜寻褪黑素。
褪黑素于1995年首次在单子叶和双子叶可食植物科中被发现（Dubbels 等，1995;Hattori等，1995）。
吲哚胺是目前所知中一种普遍存在和保守的化合物，在进化相差巨大的生物体中被发现：细菌，单和多细胞藻类，真菌，高等植物，无脊椎动物和脊椎动物(Posmyk和Janas 2009).在脊椎动物中，褪黑素是主要由松果体产生并周期性地分泌到血液中。
托福阅读生物类背景知识及真题
托福阅读生物类背景知识及真题生物类话题是托福阅读中最常见话题之一，当然对于生物的考察也不仅仅局限于陆地，还会延伸至海洋，说到海洋生物，大家对珊瑚(coral)一定并不陌生，但是珊瑚礁(coral reef)是如何形成、又如何分类呢?今天我们就一起来看一看托福阅读生物类背景知识及真题。
托福阅读生物类背景知识珊瑚礁珊瑚礁(coral reef)是指造礁石珊瑚群体死后其遗骸(remains)构成的岩体。
珊瑚礁的主体是由珊瑚虫(polyp)组成的。
珊瑚虫是海洋中的一种腔肠动物在生长过程中能吸收海水中的钙和二氧化碳，然后分泌出石灰石(limestone)，变为自己生存的外壳。
每一个单体的珊瑚虫只有米粒那样大小，它们一群一群地聚居在一起，一代代地新陈代谢(metabolism)，生长繁衍，同时不断分泌出石灰石，并粘合在一起。
这些石灰石经过以后的压实、石化，形成岛屿和礁石，也就是所谓的珊瑚礁(coral reef)。
达尔文根据礁体与岸线的关系，划分出岸礁(fringing reef)、堡礁(barrier reef)和环礁(atoll)。
fringing reef暗礁沿大陆(mainland)或岛屿(island)岸边(shore)生长发育，亦称裙礁或边缘礁。
现代最长的岸礁沿红海沿岸发育，绵延约2700多公里，分布水深约36米。
中国台湾恒春半岛和海南岛沿岸也有岸礁发育。
barrier reef堡礁又称堤礁，是离岸有一定距离的堤状礁体，它与陆地隔以泻湖(环礁湖)(lagoon)。
现代规模最大的堡礁是澳大利亚昆士兰大堡礁，全长约2022公里，分布水深约30米。
atoll环礁礁体呈环带状围绕泻湖(lagoon)，有的与外海有水道相通。
环礁直径在几百米至几十公里，形态多样。
已知的环礁有330个之多,主要分布在西太平洋的信风带和印度洋热带海域。
环礁多坐落在大洋火山锥上，孤立于大海之中，展布受洋底火山(volcano)作用的控制，某些也可在大陆架(continental shelf)上见到。
托福阅读——睡眠的秘密-1
托福阅读——睡眠的秘密-1The Secrets of SleepFrom birth, we spend a third of our lives asleep. After decades of research, we’re still not sure why.By D. T. MaxPhotograph by Maggie SteberCheryl Dinges is a 29-year-old Army sergeant from St. Louis. Her job is to train soldiers in hand-to-hand combat. Specializing in Brazilian jujitsu, Dinges says she is one of the few women in the Army certified at level 2 combat. Level 2 involves a lot of training with two attackers on one, she explains, with the hope of "you being the one guy getting out alive."Dinges may face an even harder fight in the years ahead. She belongs to a family carrying the gene for fatal familial insomnia. The main symptom of FFI, as the disease is often called, is the inability to sleep. First the ability to nap disappears, then the ability to get a full night's sleep, until the patient cannot sleep at all. The syndrome usually strikes when the sufferer is in his or her 50s, ordinarily lasts about a year, and, as the name indicates, always ends in death. Dinges has declined to be tested for the gene. "I was afraid that if I knew that this was something I had, I would not try as hard in life. I would allow myself to give up."FFI is an awful disease, made even worse by the fact that we know so little about how it works. After years of study, researchers have figured out that in a patient with FFI, malformed proteins called prions attack the sufferer's thalamus, a structure deep in the brain, and that a damaged thalamus interferes with sleep. But they don't know why this happens, or how to stop it, or ease its brutal symptoms. Before FFI was investigated, most researchers didn't even know the thalamus had anything to do with sleep. FFI is exceedingly rare, known in only 40 families worldwide. But in one respect, it's a lot like the less serious kinds of insomnia plaguing millions of people today: It's pretty much a mystery.If we don't know why we can't sleep, it's in part because we don't really know why we need to sleep in the first place. We know we miss it if we don't have it. And we know that no matter how much we try to resist it, sleep conquers us in the end. We know that seven to nine hours after giving in to sleep, most of us are ready to get up again, and 15 to 17 hours after that we are tired once more. We have known for 50 years that we divide our slumber between periods of deep-wave sleep and what is called rapid eye movement (REM) sleep, when the brain is as active as when we're awake, but our voluntary muscles are paralyzed. We know that all mammals and birds sleep. A dolphin sleeps with half its brain awake so it can remain aware of its underwater environment. When mallard ducks sleep in a line, the two outermost birds are able to keep half of their brains alert and one eye open to guard against predators. Fish, reptiles, and insects all experience some kind of repose too.All this downtime comes at a price. An animal must lie still for a great stretch of time, during which it is easy prey for predators. What can possibly be the payback for such risk? "If sleep doesn't serve an absolutely vital function," the renowned sleep researcher Allan Rechtschaffen once said, "it is the greatest mistake evolution ever made."The predominant theory of sleep is that the brain demands it. This idea derives in part from common sense—whose head doesn't feel clearer after a good night's sleep? But the trick is to confirm this assumption with real data. How does sleeping help the brain? The answer may depend on what kind of sleep you are talking about. Recently, researchers at Harvard led by Robert Stickgold tested undergraduates on various aptitude tests, allowed them to nap, then tested them again. They found that those who had engaged in REM sleep subsequently performed better in pattern recognition tasks, such as grammar, while those who slept deeply were better at memorization. Other researchers have found that the sleeping brain appears to repeat a pattern of neuron firing that occurred while the subject was recently awake, as if in sleep the brain were trying to commit to long-term memory what it had learned that day.Such studies suggest that memory consolidation may be one function of sleep. Giulio Tononi, a noted sleep researcher at the University of Wisconsin, Madison, published an interesting twist on this theory a few years ago: His study showed that the sleeping brain seems to weed out redundant or unnecessary synapses or connections. So the purpose of sleep may be to help us remember what's important, by letting us forget what's not.Sleep is likely to have physiological purposes too: That patients with FFI never live long is likely significant. A lot of interest has focused on what exactly kills them, but we still don't know. Do they literally die from lack of sleep? And if not, to what extent does sleeplessness contribute to the conditions that kill them? Some researchers have found that sleep deprivation impedes wound healing in rats, and others have suggested that sleep helps boost the immune system and control infection. But these studies are not conclusive.In the most famous attempt to figure out why we sleep, in the 1980s, Rechtschaffen forced rats to stay awake in his University of Chicago lab by placing them on a disk suspended on a spindle over a tank of water. If the rats fell asleep, the disk would turn and throw them in the water; when they fell into the water, they immediately woke up. After about two weeks of this strictenforce m ent of sleeplessness, all the rats were dead. But when Rechtschaffen performed necropsies on the animals, he could not find anything significantly wrong with them. Their organs were not damaged; they appeared to have died from exhaustion—that is, from not sleeping. A follow-up experiment in 2002, with more sophis t icated instruments, again failed to find "an unambiguous cause of death" in the rats.。
新托福阅读背景知识精选整合
新托福阅读背景知识精选整合新托福阅读背景知识：P53What is p53?After the identification of the p53 protein and the subsequent cloning of p53 genes from several species, early observations suggested that p53 may function as an ontogeny, because over expression of p53 appeared to cause monogenic transformation of cells. In the late 1980s, however, several critical discoveries defined the normal function of p53 to be anti-monogenic. Wild-type p53 genes, when introduced into cells, were found to be growth suppressive. The screening of DNA from colon cancer patients revealed that p53 mutations occur with unusually high frequency in tumor tissue, an observation that was extended to most of the other major forms of human cancer. Indeed, members of Li-Freemen cancer-prone families were shown to carry germ-line p53 mutations. The importance of these observations was underscored by the finding that mice that are homozygous null for p53, although developmentally competent, are highly predisposed to tumors.The functional character of the p53 protein was determined by experiments showing that p53 contains a strong transcriptional activation domain within its amino terminus and that it is a tetramer, sequence-specific DNA-biding protein with a defined cognate binding site containing two copies of the 10-mer (5'-RRRCA/TT/AGYYY-3'). Although the p53 protein acts as a transcriptional activator of genes containing p53-binding sites, it is also capable of strongly inhibiting transcription from many genes lacking p53-binding sites. Several monogenic DNA viruses express viral gene products that associate with and inhibit the trans-activation function of p53, notably SV40 large T antigen, the adenovirusE1B 55-kD protein, and the E6 protein of monogenic forms of human papillomavirus (HPV E6). In cells, p53 can associate with a 90-kD protein, identified as the product of the mdm-2 ontogeny, which is amplified in some types of tumors. When bound to mdm-2, p53 can no longer function as an activator of transcription.P53 plays multiple roles in cells. Expression of high levels of wild-type (but not mutant) p53 has two outcomes: cell cycle arrest or apoptosis. The observation that DNA-damaging agents induce levels of p53 in cells led to the definition of p53 as a checkpoint factor, akin, perhaps, to the product of the fad9 gene in yeast. While dispensable for viability, in response to geotaxis stress, p53 acts as an “emergency brake" inducing either arrest or apoptosis, protecting the genome from accumulating excess mutations. Consistent with this notion, cells lacking p53 were shown to be genetically unstable and thus more prone to tumors.(中文版)p53是存在人体细胞内的一种抗癌白质，它有抑制细胞生长及维持遗传物质完整性的功能。
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托福阅读背景知识之褪黑素
褪黑素与我们的睡眠质量密切相关，下面的新托福考试阅读资料要讨论的就是褪黑素有助睡眠的原因。
Melatonin, sometimes called “the hormone of darkness,” plays an important role in regulating our daily sleep patterns. This hormone is produced by our bodies and in most organisms melatonin production is higher during the night than during the day.
褪黑素，又名黑素细胞凝集素的荷尔蒙，在调节我们日常睡眠规律中扮演重要角色。
人体自身分泌褪黑激素，而且大多数生物夜晚比白天分泌得更多。
In addition to their body’s own melatonin, many people take melatonin supplements in an attempt to help them sleep, fight jet lag or balance out seasonal affective disorder.
此外，一些人通过体外补充褪黑素改善睡眠，缓解飞机时差感、平衡季节性情绪失调。
Melatonin And Memories
褪黑素对记忆的影响
But a study by a group of scientists at the University of Houston suggests that melatonin might have a negative impact on the ability to form new memories.
但是，休斯顿大学的科学家们研究表明：褪黑素阻碍记忆形成。
The researchers were interested in how the body’s internal clock affects the formation of new memories. They found that small striped minnows called zebra fish learned very well during the day but very poorly at night, when melatonin levels are higher.
研究人员想弄清楚体内生物钟如何影响新生记忆的形成。
研究人员发现斑马鱼白天学习能力很好;夜晚却很差，而夜晚褪黑素分泌旺盛。
They wondered if melatonin played a role in learning and memory.
研究人员怀疑褪黑素影响学习和记忆。
Melatonin And Learning
褪黑素对学习的影响
They treated zebra fish with extra melatonin during the day, boosting the hormone levels to night-time amounts.
白天，研究人员喂给斑马鱼褪黑素，促进斑马鱼夜晚褪黑素分泌。
They discovered that high melatonin did not affect learning per se, but dramatically reduced the fishes’ ability to for m new memories, or to remember what they’d learned.
研究人员发现大量的褪黑素没有直接影响学习本身，但是却很大程度地使斑马鱼的记忆衰退，斑马鱼不记得学过的东西。
Then the scientists inhibited melatonin activity in the fish. They did this by blocking melatonin receptors with inhibitory drugs. The fishs’ mela tonin levels were unchanged, but the ability of melatonin to affect the brain was blocked.
接着，科学家们抑制斑马鱼体内的褪黑素的作用：抑制药物阻碍褪黑素受体。
斑马鱼褪黑素分泌量没改变，但是褪黑素不能影响不了大脑。
Blocking Melatonin
阻碍褪黑素
With melatonin activity blocked, the ability of the fish to form new memories was drastically improved, even at night.
褪黑素的作用受阻，斑马鱼新生记忆能力明显改善，夜晚也很好。
This research has potential benefits for humans. For example, the use of melatonin receptor blockers could improve performance of night-time cognitive tasks, helping people such as night-shift workers or students cramming for exams.
该项研究带给人类潜在好处。
例如，褪黑素受体的阻碍能影响人夜晚的认知能力，那么对于那些夜班工作者和熬夜备考的学生都有所帮助。
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