Wisdom in old age depends on a fresh supply of new brain cells, a study in mice suggests. When mature mice learn a new task, their newly generated brain cells are three times more active than their old ones, the researchers found. The findings add to a growing body of evidence that the adult brain needs a steady addition of new cells to maintain its mental faculties. Paul Frankland at the Hospital for Sick Children in Toronto, Ontario, Canada, and colleagues injected a group of mice with a chemical agent that stains only those cells born in the animals' brains at the time of injection. One week later, the team taught some of the mice how to navigate through a maze (迷宫), before sacrificing them to analyse the cells in a region of the brain called the hippocampus(海马体),which is key to learning and memory. In stages, the rest of the mice also underwent this paired process of learning and hippocampal examination at increasing time intervals from the initial injection. Frankland's team analysed the mice's stained hippocampal cells for key proteins—evidence that the cells were active and forming the new neural connections vital for learning. The team found that the stained cells had undergone significantly more activity in the mice that had learned the maze soon after the injection-when the stained cells were newly generated. For example, those that had learned the maze six weeks after the injection had three times as much "activity" in their stained cells as those mice that learned the maze eight weeks after injection, when the stained cells were fully mature. Cells examined at less than six weeks' old at the time of learning did not show as much activity as at six weeks, however. According to Frankland, this suggests that when neurons reach six weeks of age they are specifically recruited to form the brain networks that support new memories. "The results strengthen the link between new cells in the adult brain and learning-and shows more convincingly that they have a functional role," Frankland says. He believes the study is the first to provide positive evidence that newly generated brain cells are more active than old ones.
单选题
What can we know about the findings of the study conducted in the Hospital for Sick Children in Toronto?
单选题
What can show that the cells were active and forming the new neural connections vital for learning?
【正确答案】
B
【答案解析】根据题干可以定位到第四段第一句：Frankland's team analysed the mice's stained hippocampal cells for key proteins—evidence that the cells were active and forming the new neural connections vital for learning(弗兰克兰德的研究团队分析了实验鼠的被改变的海马体细胞，已找到重要的蛋白质——这些蛋白质能够证明这些细胞处于活跃状态，并且形成了新的对学习过程非常重要的神经联结)，可见本题的正确答案为B。
单选题
What can we learn from the passage?
【正确答案】
D
【答案解析】浏览选项后发现，选项的内容是与原文第四、五段的内容相联系的。第四段最后一句说：soon after the injection—when the stained cells were newly generated(在注射完成后不久——就是被改变的细胞刚刚产生的时候)，很显然D项的内容是与此相符的，因此为正确答案。对照其他三个选项和第五段的内容会发现，这三个选项与原文的叙述都不符，故排除。