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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.
A rapid relief from symptoms in the second research contrasts with how long it took the first team to create the symptoms in their mice because______.
选项 A、the types of mice used by the two teams were different
B、the neural circuits they examined were different
C、the types of mice used and the neural circuits examined were different
D、the types of mice used and the broad brain area examined were different
答案C
解析 本题考查考生对最后一段关于两个实验结果差异的现象以及原因的理解。最后一段讲到一个现象，那就是第二个实验中出现了强迫症症状可以迅速缓解的现象，而第一个实验中哥伦比亚小组花了很长时间才在小鼠身上建立症状，本题考查的即是这个差异的原因。题目本身不难，因为最后明确给出了原因，即这可能是因为两个团队使用的小鼠类型不同，而且，两个团队观察的神经回路不同，因此选择[C]。[A]和[B]都只是给出了部分原因，因此不正确。[D]是错误理解，文中指明了虽然两个实验研究的脑部大的区域是相同的，但是具体的神经回路不同，[D]后半句说法错误。
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