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Scientist Paul Johnson and his team did a research on the result of feeding a lot of junk food to some rats. They had a serious goal: to try to understand how parts of the brain play a role in obesity. (Obesity is the condition of being very overweight, which has been linked to a variety of health problems.) The scientists observed that the more junk food the rats ate, the more they wanted to eat—a behavior very similar to that of rats addicted to heroin, a dangerous drug. Johnson told Science News the experiment shows that the brain chemistry of obesity and drug addiction may be quite similar.
In their experiment, Johnson and his team studied the “pleasure center” of rats’ brains. The pleasure center is a complicated network of nerve cells. Together, these cells work as the body’s reward system. If the animal exercises or eats, the cells reward the animal by releasing chemicals into the body that make it feel good. And when the body feels good, the animal—or person—will want to do the behavior again. Pleasure centers can release these chemicals in less healthy ways, too. Drugs like heroin can cause the pleasurable chemicals to be released.
For the experiment, Johnson fed foods like cheesecake, bacon and Ho Hos to one group of rats. These foods are all high in calories and high in fat. Another group of rats received a regular, nutritious diet. The rats that ate junk food started to eat more and more.
【題組】77. What is the result to the rats that are fed with junk food?
(A) They live longer. (B) They are addicted to heroin.
(C) They want to eat more junk food. (D) They change to a regular, nutritious diet.
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