Book 2 Listening (1108796), страница 12
Текст из файла (страница 12)
All showed that inconsistent sleepingschedules went hand in hand with poor academic performance. Surprisingly, however, littlesuch research had been done on children.She and a team of colleagues therefore examined the bedtimes and cognitive abilitiesof 11,178 children born in Britain between September 2000 and January 2002, who areenrolled in a multidisciplinary research project called the Millennium Cohort Study.
Thebedtime information they used was collected during four visits interviewers made to thehomes of those participating in the study. These happened when the children were ninemonths, three years, five years and seven years of age. Besides asking whether the childrenhad set bedtimes on weekdays and if they always, usually, sometimes or never made them,interviewers collected information about family routines, economic circumstances and othermatters - including whether children were read to before they went to sleep and whether theyhad a television in their bedroom.
The children in question were also asked, at the ages ofthree, five and seven, to take standardised reading, mathematical and spatial-awarenesstests, from which their IQs could be estimated.Dr Kelly's report, just published in the Journal of Epidemiology and Community Health,shows that by the time children had reached the age of seven, not having had a regularbedtime did seem to affect their cognition, even when other pertinent variables such asbedtime reading, bedroom televisions and parents' socioeconomic status were controlled for.But that was true only if they were female.
On the IQ scale, whose mean value is 100points, girls who had had regular bedtimes scored between eight and nine points more thanthose who did not.Boys were not completely unaffected. Irregular bedtimes left their IQs about six pointsbelow those of their contemporaries at the age of three. But the distinction vanished by thetime they were seven.This difference between the sexes is baffling. Dr Kelly did not expect it and has noexplanation to offer for it. As scientists are wont to say, but this time with good reason, moreresearch is necessary.Meanwhile, in the going-to-bed wars most households with young children suffer, thesons of the house have acquired extra ammunition.
Mind you, those with the no us to readand understand Dr Kelly's results are probably not suffering from their sleep regimes anyway.(From The Economist, July 13, 2013)Script 16. How siestas help memorySleepy headsResearchers say an afternoon nap prepares the brain to learnMad dogs and Englishmen, so the song has it, go out in the midday sun. And thebusiness practices of England's lineal descendant, America, will have you in the office fromnine in the morning to five in the evening, if not longer. Much of the world, though, prefers totake a siesta. And research presented to the AAAS meeting in San Diego suggests it may beright to do so.50It has already been established that those who siesta are less likely to die of heartdisease.
Now, Matthew Walker and his colleagues at the University of California, Berkeley,have found that they probably have better memory, too. A post-prandial snooze, Dr Walkerhas discovered, sets the brain up for learning.The role of sleep in consolidating memories that have already been created has beenunderstood for some time. Dr Walker has been trying to extend this understanding by lookingat sleep's role in preparing the brain for the formation of memories in the first place. He wasparticularly interested in a type of memory called episodic memory, which relates to specificevents, places and times.
This contrasts with procedural memory, of the skills required toperform some sort of mechanical task, such as driving. The theory he and his team wanted totest was that the ability to form new episodic memories deteriorates with accruedwakefulness, and that sleep thus restores the brain's capacity for efficient learning.They asked a group of 39 people to take part in two learning sessions, one at noon andone at 6 pm. On each occasion the participants tried to memorise and recall 100combinations of pictures and names. After the first session they were assigned randomly toeither a control group, which remained awake, or a nap group, which had 100 minutes ofmonitored sleep.Those who remained awake throughout the day became worse at learning.
Those whonapped, by contrast, actually improved their capacity to learn, doing better in the eveningthan they had at noon. These findings suggest that sleep is clearing the brain's short-termmemory and making way for new information.It is already well known that fact-based memories are stored temporarily in an areacalled the hippocampus, a structure in the centre of the brain.
But they do not stay there long.Instead, they are sent to the prefrontal cortex for longer-term storage.Electroencephalograms, which measure electrical activity in the brain, have shown that thismemory-refreshing capacity is related to a specific type of sleep called Stage 2 non-REMsleep.The ideal nap, then, follows a cycle of between 90 and 100 minutes.
The first 30minutes is a light sleep that helps improve motor performance. Then comes 30 minutes ofstage 2 sleep, which refreshes the hippocampus. After this, between 60 and 90 minutes intothe nap, comes rapid-eye movement, or REM, sleep, during which dreaming happens. This,research suggests, is the time when the brain makes connections between the newmemories that have just been "downloaded" from the hippocampus and those that alreadyexist - thus making new experiences relevant in a wider context.The benefits to memory of a nap, says Dr Walker, are so great that they can equal anentire night's sleep. He warns, however, that napping must not be done too late in the day orit will interfere with night-time sleep. Moreover, not everyone awakens refreshed from asiesta. The grogginess that results from an unrefreshing siesta is termed "sleep inertia".
Thishappens when the brain is woken from a deep sleep with its cells still firing at a slow rhythmand its temperature and blood flow decreased.Sara Mednick, from the University of California, San Diego, suggests that non-habitualnappers suffer from this more often than those who siesta regularly. It may be that those whohave a tendency to wake up groggy are choosing not to siesta in the first place. Perhaps,though, as in so many things, it is practice that makes perfect. (From The Economist,February 27, 2010)Script 17. RestlessA strange case raises the question of what sleep is forThe function of sleep, according to one school of thought, is to consolidate memory. Yettwo Italians have no problems with their memory even though they never sleep.
The womanand man, both in their 50s, are in the early stages of a neurodegenerative disease calledmultiple system atrophy. Their cases raise questions about the purpose of sleep.Healthy people rotate between three states of vigilance: wakefulness, rapid eyemovement (REM) sleep and non-REM sleep. But all three are mixed together in the Italian51patients. The pair were initially diagnosed by Roberto Vetrugno of the University of Bolognaand his colleagues as suffering from REM behavioural disorder, in which the paralysis, orcataplexy, that normally prevents sleeping people from acting out their dreams is lost.
Thiscan cause people in REM sleep to twitch and groan, sometimes flailing about and injuringtheir bedmates. These patients, however, soon progressed from this state to an even odderone, according to a report in Sleep Medicine.One of the principal ways to measure sleep is to monitor brainwave activity, which canbe done by placing electrodes on the scalp in a technique known as electroencephalography(EEG). Non-REM sleep itself is divided into four stages defined purely by EEG patterns; thefirst two are collectively described as light sleep and the last two as deep or slow-wave sleep.When the Italian patients appeared to be asleep, their EEGs suggested that their brains wereeither simultaneously awake, in REM sleep and non-REM sleep, or switching rapidly betweenthe three.
Yet when subjected to a battery of neuropsychological tests, they showed nointellectual decline.Mark Mahowald of the University of Minnesota Medical School, whose group firstdescribed REM behavioural disorder in 1986, thinks memory consolidation is still going on inthe brains of the two Italian patients; hence their lack of cognitive impairment or dementia.What needs to be revised in light of their cases, he says, is the definition of sleep.Dr Mahowald suspects that sleep can occur in the absence of the markers that currentlydefine it, which means those markers are insufficient. What’s more, the Italian cases lendsupport to an idea that has been gathering steam in recent years: that wakefulness and sleepare not mutually exclusive.
In other words, the human brain can be awake and asleep at thesame time.That evidence takes the form of a growing list of conditions in which wakefulness, REMand non-REM sleep appear to be mixed. An example is narcolepsy, in which emotionallyladen events trigger sudden cataplexy. When the dreaming element of REM intrudes intowakefulness, which can happen with sleep deprivation, the result is wakeful dreaming orhallucinations.
Since such dreams can be highly compelling, Dr Mahowald thinks they mightaccount for some reports of alien abduction.But there is another possible explanation of the Italian puzzle: that sleep is notnecessary for memory after all. Jerry Siegel of the University of California, Los Angeles, hasstudied the sleep habits of many animals and thinks that could well be the explanation. All ofwhich gives researchers something new to keep them awake at night. (From The Economist,September 18, 2008)52Unit 8. CoffeeScript 18. Salt-tolerant riceNuclear-powered cropsPhysics meets biology in a project to breed better strains of riceThose who turn their noses up at "genetically modified" food seldom seem to considerthat all crops are genetically modified. The difference between a wild plant and one thatserves some human end is a lot of selective breeding - the picking and combining over theyears of mutations that result in bigger seeds, tastier fruit or whatever else is required.Nor, these days, are those mutations there by accident.
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