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  3. Researchers have both created and relieved symptoms of obsessive-compulsive disorder(OCD)in genetically modified mice using a te

Researchers have both created and relieved symptoms of obsessive-compulsive disorder(OCD)in genetically modified mice using a te

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问题     Researchers have both created and relieved symptoms of obsessive-compulsive disorder(OCD)in genetically modified mice using a technique that turns brain cells on and off with light, known as optogenetics. The work, by two separate teams, confirms the neural circuits that contribute to the condition and points to treatment targets. It also provides insight into how quickly compulsive behaviors can develop—and how quickly they might be soothed.
    Brain scanning in humans with OCD has pointed to two areas—the orbitofrontal cortex, just behind the eyes, and the striatum, a hub in the middle of the brain—as being involved in the condition’ s characteristic repetitive and compulsive behaviors. But "in people we have no way of testing cause and effect", says Susanne Ahmari, a psychiatrist and neuroscientist at Columbia University in New York who led one of the studies. It is not clear, for example, whether abnormal brain activity causes the compulsions, or whether the behavior simply results from the brain trying to hold symptoms at bay by compensating.
    Ahmari’s team wanted to see if optogenetics could prompt repetitive grooming in mice. The team injected viruses into the orbitofrontal cortex carrying genes for light-sensitive proteins. The researchers then inserted an optical fiber to shine a light on these cells for a few minutes a day. It was only after a few days that they started to see the compulsive behavior.
    In the second study, researchers at the Massachusetts Institute of Technology(MIT)in Cambridge used a mouse model of repetitive behavior in which the mice carried a mutation in a gene involved in creating neuronal connections. The researchers conditioned both mutant and control mice to groom when water was dripped on their foreheads. After a series of trials, the mutants began to groom even without a water drop.
    The team then used optogenetics to stimulate neurons in the orbitofrontal cortex that feed into the striatum. This is a similar but not overlapping group of cells to the neural circuit studied by Ahmari’s team. "Within a matter of a second or two, a behavioral change occurs," says Ann Graybiel, who co-authored the MIT study. The abnormal grooming disappeared, leaving behind only the normal reaction to the water drop.
    She was doubly surprised that the cortex—the area associated with executive, even conscious control of behavior—could be at the root of such an automatic response. "Everybody has thought that when we get these compulsive behaviors or really strong habits, then these behaviors reel off by themselves," she says. Instead, the orbitofrontal cortex can send a "stop" signal to other brain regions concerned with more automatic movements.
    Such a rapid relief from symptoms contrasts with how long it took the Columbia team to create the symptoms in their mice. This could have been related to the fact that the types of mice used by the two teams were different, Ahmari says, and that they examined slightly different circuits, albeit within the same broad areas.
The underlined phrase "real off" in Paragraph 6 is closest in meaning to______.
选项 A、pause
B、discontinue
C、reappear
D、repeat
答案D
解析 本题考查考生对生词意思的理解。“reel off”本意指“一口气说出，背诵”，这个短语出现在第六段第二句，第六段讲到第二个实验研究人员的体会，她说：“每个人都认为，当我们产生这种强迫行为或非常牢固的习惯，这些行为就不断的自我______。”然而取而代之的是，前额皮层更加自动地发送“停止”信号到大脑其它相关区域。后句是全句的转折，后面说事实是前额皮层更加自动地发送“停止”信号到大脑其它相关区域，可见，前面人们普遍认为的是强迫行为或者非常牢固的习惯可以不断自我重复，因此选择[D]。[A][B]可以根据以上的理解直接排除，[C]的再现与重复有一定相似性，但是再现只是再次出现，并不强调行为的多次出现，因此也不正确。
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