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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.
Which two areas were involved in the condition’s characteristic repetitive and compulsive behaviors?
选项 A、the orbitofrontal cortex and the striatum
B、eyes and the striatum
C、the orbitofrontal cortex and foreheads
D、the striatum and a hub in the middle of the brain
答案A
解析 本题考查考生对第二段中有关实验得出的与重复性和强迫性的行为症状有联系的区域的把握。第二段第一句明确指出这两个区域是前额皮层和纹状体，并且分别对这两个专有名词给出了通俗的解释，即：前额皮层，在眼睛位置的正后方；纹状体，在大脑中央位置的一个枢纽。显然[A]是正确答案。[B]中眼睛并不是区域之一，[C]中额头不是区域之一，[D]中纹状体就是位于大脑中央位置的一个枢纽，说的是一码事，因此均不正确。
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