单项选择题

People who are extremely careful and "finish what they start" may have a reduced risk of developing Alzheimer’s disease, according to a study involving Catholic nuns and priests.
The most conscientious and self-disciplined individuals were found to be 89% less likely to develop this form of dementia—deterioration of intellectual faculties, such as memory, concentration, and judgment, resulting from an organic disease or a disorder of the brain—than their peers over the course of the 12-year study.
Robert Wilson at Rush University Medical Center in Chicago, Illinois, US, and colleagues followed 997 healthy Catholic nuns, priests and Christian brothers between 1994 and 2006. Early on in the study, participants completed a personality test to determine how conscientious they were.
Based on answers to 12 questions such as "I am a productive person who always gets the job done", they received a score ranging from 0 to 48. On average, volunteers scored 34 points in the test.
Volunteers also underwent regular neurological examinations and cognitive tests. Over the lifetime of the study, 176 of the 997 participants developed Alzheimer’s disease. However, those with the highest score on the personality test—40 points or above—had an 89% lower chance of developing the debilitating condition than participants who received 28 points or lower.
"These are people who control impulses, and tend to follow norms and roles," Wilson told New Scientist.
Previous studies suggest that exercise and intellectual stimulation can decrease the risk of Alzheimer’s disease. But the link between self-discipline and a reduced risk of the illness remained strong even after researchers discounted these factors from their study. Subjects still had a 54% lower chance of developing the condition.
Exactly why conscientiousness should have an impact on Alzheimer’s risk remains unclear, says Wilson. He notes that brain autopsies conducted on 324 of the study’s participants failed to resolve the mystery.
Earlier work has linked the presence of plaques and protein tangles within the brain to Alzheimer. Yet, in general, the brains of those who scored highly on the conscientiousness test had as many plaques and protein tangles as those of subjects who scored lower.
Wilson suggests that more careful and conscientious individuals may have more active frontal brain regions, an area that is responsible for decision-making and planning. Increased activity in this region may perhaps compensate for a decline in function in other brain regions, he speculates. Based on the new findings, doctors could perhaps consider certain patients at greater risk of dementia, says Ross Andel at the University of South Florida, US. "This is a study about identifying people at risk," he says.
According to the study, which one of the personalities below is more closely related to Alzheimer’s disease