题目内容：
Just as exercise strengthens the heart and lungs, bones and muscles, it may also power up the brain. A succession of scientific studies of animals implies that physical activity has a positive effect on mental functioning. “It’s clear that the brain benefits from exercise,” says brain scientist William Greenough of the University of Illinois at Urbana-Champaign. His studies with rats have demonstrated two primary effects of activity: vigorous physical exercise provides the brain with more fuel, and skill-based exercise increases the formation of connections in the brain, which, according to the proposals of some scientists, may make the brain better able to process information. In one experiment, laboratory rats were separated into three groups. One group was exercised by running inside an automatic wheel, a second group improved their skills in a complicated obstacle course, and a third group was inactive. “The animals that learned to go through the obstacle course exhibited a greater number of brain connections than the animals in the exercised or inactive groups,” Greenough said. “In contrast, the animals that exercised inside the automatic wheel possessed a greater density of blood vessels in the brain than did either of the other two groups of animals.”Learning a new dance step may boost the brain in the same way that learning a language can, he says. And if the dance
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