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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.
According to the passage, which one of the following is true of the second study—MIT team?
选项 A、The researchers injected viruses into the orbitofrontal cortex carrying genes for light-sensitive proteins.
B、The researchers inserted an optical fiber to shine a light on these cells for a few minutes a day.
C、The researchers used a mouse model of repetitive behavior in which the mice carried a mutation in a gene involved in creating neuronal connections.
D、The researchers conditioned both mutant and control mice to groom when water was dripped on their feet.
答案C
解析 本题考查考生对文中所述两个实验研究的理解和把握。题目考查的是关于第二项实验研究哪一个说法是正确的。文章从第四段开始介绍第二项实验，第四段第一句就指出在第二项研究中，剑桥的麻省理工学院(MIT)的研究人员使用了重复行为的小鼠模型，这些小老鼠携带了参与生成神经元连接的变异基因。因此，[C]是正确选项。第四段接下来说道，研究人员设法使变异基因组和参照组的小鼠当水滴落到他们前额时作出梳理动作，而非脚上，因此[D]错误。[A]和[B]选项都出现在文章的第三段，都是关于第一项实验研完的描述，而非第二项，因此均不正确。
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