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Birds that are literally half-asleep—with one brain hemisphere alert and the other sleeping—control which side of the brain rema

admin2009-06-24  58
问题     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% of dozing time versus about 12% 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 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". He speculates that more examples may turn up when we take a closer look at other species.
选项 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
答案C
解析 由题干中的关键短语A new study回查文章中相关的句子，即第一段第一句话，"处于半睡眠状态，即一个大脑半球休息，而另一个半球则保持清醒的鸟类能控制着那一半球的大脑保持清醒"。即能自觉或自主地(consciously)控制大脑半球的睡眠。
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