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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 first paragraph, ______contribute to symptoms of obsessive-compulsive disorder.
选项 A、light-sensitive proteins
B、neural circuits
C、abnormal brain activities
D、optical fibers
答案B
解析 本题考查考生对第一段内容的理解。第一句引入实验研究的对象——强迫症症状，介绍了实验采取的方法。第二句介绍实验的结果，即定位了“能够影响病情同时也是治疗目标的神经回路”，而这里的病情以及治疗目标就是上一句所说的强迫症症状，所以也就是说神经回路影响了强迫症症状，因此选[B]。[A]选项出现在第三段，“研究团队将携带光敏感蛋白的病毒注入到前额皮层”，可见光敏感蛋白是实验之一所采用的试剂，并不是促成强迫症症状的因素。[C]选项出现在第二段，实验者在解释为何不能在人体实验时讲到，目前尚不清楚是否有异常的脑活动导致了强迫症症状，因此也不正确。[D]与[A]选项一样出现在第三段，而且也是研究人员注入实验对象的一种物质，而非促成强迫症的因素，因此错误。
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