Unit 3 Under the sea grammar课时作业

第一节 阅读理解

　　A so-called "smart drug" intended to improve cognitive(认知的) performance also seems to protect the brain from altitude sickness.

　　Even more people are visiting high-altitude sites for work, sport, religious pilgrimages and military tasks. But even the fittest among us suffer in thin air:the lower oxygen content at the altitude can lead to cognitive effects, including memory loss and attention difficulties.

　　There's little you can do to prevent these symptoms other than acclimatize-but this takes time and doesn't always work. A drug called oxiracetam might be the answer.

　　ShengLi Hu at the Third Military Medical University, Chongqing, China and her colleagues studied the performance of male military personnel at altitude. All lived in towns around 1,800 meters above sea level. During the study, they spent eight days at this altitude and then climbed for three days to reach 4,000 meters, where they stayed for up to a month.

　　Twenty participants took oxiracetam three times a day for the first 15 days of the study, while another 20 received no intervention. The man did tests of attention and memory at the start and end of the study and 20 days in, by which time they had been at 4,000 meters for nine days.

　　While all the participants experienced a drop in cognitive ability at 4,000 meters, those who took oxiracetam showed a much smaller decline than the control group.

　　Blood flow measurements indicated that at high altitude, parts of the brain's cerebral circulatory system contracted and dilated (扩张) in a way that promoted blood flow to the brain stem. This isn't surprising, since the brain stem plays a critical role in the maintenance of basic vital signs.

The team also found that the brain stem received blood at the expense of areas responsible for more advanced cognitive functions. But in people who took oxiracetam, more arteries dilated, so blood flow throughout the brain rose. This may