根据下列文章,请回答 41～45 题。 High Stress May Damage Memory A ccording to a report issued in May 1998，elderly people who have consistency high blood levels of cortisol(皮质醇)don’t score as well on memory tests as their peers with lower levels of the stress hormone．What’s more．high levels of cortisol are also associated with shrinking of the hippocampus(海马区)，a region of the brain that plays a key role in learning and memory． The findings suggest that even cortisol levels in the normal，“healthy” range can actually accelerate brain aging． The study results” now provide substantial evidence that long—term exposure to adrenal(肾上腺的)stress hormones may promote hippocampal aging in normal elderly humans。”write Nada Porter and Philip Land field．Cortisol is a hormone released in response to stress by the adrenal glands(腺)，which sit on top of the kidneys(肾)． Over a 5-to 6-year period，Dr．Sonia Lupien and his colleagues measured 24-hour cortisol levels in 51 healthy volunteers，most of whom were in their 70s． The researchers tested the volunteers’memory on six people in the increasin9/high category and five people in the decreasing/moderate group．The groups did not differ in tests of immediate memory，but the increasing/high cortisol group had other memory problems compared with those in the decreasing/moderate group． The researchers also found that the total volume of the hippocampus in those in the increasing/high group was 14%lower than those in the decreasing/moderate group，although there were no differences in other brain regions． The results suggest that“…brain aging can be accelerated by levels of adrenal hormones that are not generally regarded as pathological(病态的)and that variation within this normal range is related to variation in the rate of brain aging，”write Porter and Land field．“This further suggests that chronic stress may accelerate the worsening of{he hippocampus．” 第 41 题 Which of the following plays a key role in one’s learning and memory?