New Brain Cells Love to Learn 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. What does Frankland think of the study
A．The results are more convincing in proving the link between new cells in adult brain and learning. B．It is the first one trying to prove that newly generated brain cells are more active than old ones. C．It proves that new cells in adult brains have a functional role. D．It was conducted in a more scientific way than the studies before it.