Birds that are literally half-asleep─with one brain hemisphere alert and the other sleeping─control which side of the brain remains awake, according to a new study of sleeping ducks.
Earlier studies have documented half-brain sleep in a wide range of birds. The brain hemispheres take turns sinking into the sleep stage characterized by slow brain waves. The eye controlled by the sleeping hemisphere keeps shut, while the wakeful hemisphere s eye stays open and alert. Birds also can sleep with both hemispheres resting at once.
Decades of studies of bird flocks led researchers to predict extra alertness in the more vulnerable, end-of-the-row sleepers. Sure enough, the end birds tended to watch carefully on the side away from their companions. Ducks in the inner spots showed no preference for gaze direction.
Also, birds dozing at the end of the line resorted to single-hemisphere sleep, rather than total relaxation, more often than inner ducks did. Rotating 16 birds through the positions in a four-duck row, the researchers found outer birds half-asleep during some 32 percent of dozing time versus about 12 percent for birds in internal spots.
We believe this is the first evidence for an animal behaviorally controlling sleep and wakefulness simultaneously in different regions of the brain, the researchers say.
The results provide the best evidence for a long-standing supposition that single-hemisphere sleep evolved as creatures scanned for enemies. The preference for opening an eye on the lookout side could be widespread, he predicts. He s seen it in a pair of birds dozing side-by-side in the zoo and in a single pet bird sleeping by a mirror. The mirror-side eye closed as if the reflection were a companion and the other eye stayed open.
Useful as half-sleeping might be, it s only been found in birds and such water mammals(哺乳动物)as dolphins, whales, and seals. Perhaps keeping one side of the brain awake allows a sleeping animal to surface occasionally to avoid drowning.
Studies of birds may offer unique insights into sleep. Jerome M. Siegel of the UCLA says he wonders if birds half-brain sleep is just the tip of the iceberg(冰山). He speculates that more examples may turn up when we take a closer look at other species.
11.A new study on birds sleep has revealed that .
A) half-brain sleep is found in a wide variety of birds
B) half-brain sleep is characterized by slow brain waves
C) birds can control their half-brain sleep consciously
D) birds seldom sleep with the whole of their brain at rest
12.According to the passage, birds often half sleep because .
A) they have to watch out for possible attacks
B) their brain hemispheres take turns to rest
C) the two halves of their brain are differently structured
D) they have to constantly keep an eye on their companions
13.The example of a bird sleeping in front of a mirror indicates that .
A) the phenomenon of birds dozing in pairs is widespread
B) birds prefer to sleep in pairs for the sake of security
C) even an imagined companion gives the bird a sense of security
D) a single pet bird enjoys seeing its own reflection in the mirror
14.While sleeping, some water mammals tend to keep half awake in order to .
A) alert themselves to the approaching enemy
B) emerge from water now and then to breathe
C) be sensitive to the ever-changing environment
D) avoid being swept away by rapid currents
15.By just the tip of the iceberg , Siegel suggests that .
A) half-brain sleep has something to do with icy weather
B) the mystery of half-brain sleep is close to being sleepers
C) most birds living in cold regions tend to be half sleepers
D) half-brain sleep is a phenomenon that could exist among other species
11.C 12.A 13.C 14.B 15.D
四招帮你轻松搞定中考英语作文
中考英语之现在完成时剖析
2010中考英语重点句法考点16:状语从句
独家原创:中考英语近形词汇总(第三辑)
王培同老师原创:中考英语介词考点练习二
中考英语题型详解:补全对话突破有道
初中英语知识点解析:词类和句子成分的关系(一)
2010年北京中考英语方法指导
2010中考英语重点句法考点13:倒装句
每日一练:历年全国中考英语单项选择真题精选(2)
中考体育项目的考试技巧与策略
2010中考英语重点句法考点17:宾语从句
总结:初中英语重点反义词(组)大全
非看不可的中考高分英语写作之句子篇
中考英语夺分关键:阅读理解题
独家原创:中考英语近形词汇总(第五辑)
2010年中考英语复习指导
2010中考英语必背的20组词语辨析
2010中考英语满分秘诀(续):记住100组同义词(101-120组)
每日一练:历年全国中考英语单项选择真题精选(1)
王培同老师原创:中考英语介词考点练习三
2010中考英语满分秘诀(续):记住100组同义词(181-200组)
2010中考英语满分秘诀(续):记住100组同义词(141-160组)
轻松掌握英语八种时态的六点建议
中考英语之定语从句剖析
2010中考英语满分秘诀(续):记住100组同义词(161-180组)
中考英语句型转换解析(一)--条件型句型转换
2010中考英语满分秘诀(续):记住100组同义词(121-140组)
初中英语知识点解析:词类和句子成分的关系(二)
2010中考英语解题方法指导及例题分析
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |