单选题
Researchers investigating brain size and mental ability say their
work offers evidence that education protects the mind from the brain's physical
deterioration. It is known that the brain shrinks as the body
ages, but the effects on mental ability are different from person to person.
Interestingly, in a study of elderly men and women, those who had more education
actually had more brain shrinkage. "That may seem like bad
news," said study author Dr. Edward Coffey, a professor of psychiatry and of
neurology at Henry Ford Health System in Detroit. However, he explained, the
finding suggests that education allows people to withstand more brain-tissue
loss before their mental functioning begins to break down. The
study, published in the July issue of Neurology, is the first to provide
biological evidence to support a concept called the "reserve" hypothesis,
according to the researchers. In recent years, investigators have developed the
idea that people who are more educated have greater cognitive reserves to draw
upon as the brain tissue to spare. Examining brain scans of 320
healthy men and women ages 66 to 90, researchers found that for each year of
education the subjects had, there was greater shrinkage of the outer layer of
the brain known as the cortex. Yet on tests of cognition and memory, all
participants scored in the range indicating normal. "Everyone
has some degree of brain shrinkage," Coffey said. "People lose (on average) 2.5
percent per decade starting in adulthood." There is, however, a
"remarkable range" of shrinkage among people who show no signs of mental
decline, Coffey noted. Overall health, he said, accounts for some differences in
brain size. Alcohol or drug use, as well as medical conditions such as diabetes
and high blood pressure, contribute to brain-tissue loss throughout
adulthood. In the absence of such medical conditions, Coffey
said, education level helps explain the range of brain shrinkage exhibited among
the mentally-fit elderly. The more-educated can withstand greater
loss. Coffey and colleagues gauged shrinkage of the cortex by
measuring the cerebrospinal fluid surrounding the brain. The greater the amount
of fluid means the greater the cortical shrinkage. Controlling for the health
factors that contribute to brain injury, the researchers found that education
was related to the severity of brain shrinkage. For each year of education from
first grade on, subjects had an average of 1.77 milliliters more cerebrospinal
fluid around the brain. For example, Coffey's team reported,
among subjects of the same sex and similar age and skull size, those with 16
years of education had 8 percent to 10 percent more cerebrospinal fluid compared
with those who had four years of schooling. Of course,
achieving a particular education level is not the definitive measure of
someone's mental capacity. And, said Coffey, education can be "a proxy for many
things". More-educated people, he noted, are often less likely to have habits,
such as smoking, that harm overall health. But Coffey said that his team's
findings suggest that like the body, the brain benefits from exercise. "The
question is whether by continuing to exercise the brain we can forestall the
effects of (brain shrinkage)," he said. "My hunch is that we can."
According to Coffey, people should strive throughout life to keep their
brains alert by exposing themselves to new experiences. Traveling is one way to
stimulate the brain, he said, a less adventuresome way is to do crossword
puzzles. "A hot topic down the road," Coffey said, will be
whether education even late in life has a protective effect against mental
decline. Just how education might affect brain cells is
unknown. In their report, the researchers speculated that in people with more
education, certain brain structures deeper than the cortex may stay intact to
compensate for cortical shrinkage.
单选题
According to this passage, all of the following factors could account
for brain shrinkage EXCEPT ______.