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  3. How does food affect mood and mind? The answer may lie in the chemistry of the brain and nervous system. Molecules called neurot

How does food affect mood and mind? The answer may lie in the chemistry of the brain and nervous system. Molecules called neurot

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问题     How does food affect mood and mind? The answer may lie in the chemistry of the brain and nervous system. Molecules called neurotransmitters (神经传递素) are chemical messengers. They carry a nerve impulse across the gap between nerve cells. The release of neurotransmitter molecules from one neuron and their attachment to receptor sites on another keep a nerve impulse moving.
    Nerve impulses carry messages from the environment to the brain, for example, the pain you feel when you stub (踢碰) your toe. They also carry messages in the other direction, from the brain to the muscles. That’s why you back away from the obstacle that initiated the pain signal and exclaim, "Ouch! "
    "Many neurotransmitters are built from the foods we eat," says neuroscientist Eric Chudler of the University of Washington. Too little or too much of a particular nutrient in the diet can affect their production, Chudler says. For example, tryptophan from foods such as yogurt, milk, bananas, and eggs is required for the production of the neurotransmitter serotonin. Phenylalanine from beets, almonds, eggs, meat, and grains goes into making the neurotransmitter dopamine.
    Dozens of neurotransmitters are known; hundreds may exist. Their effects depend on their amounts and where they work in the brain. The neurotransmitter serotonin, for example, is thought to produce feelings of calmness, relaxation, and contentment. Drugs that prevent it from being taken again (into the neuron that released it) are prescribed to treat depression. In at least some healthy, nondepressed people, carbohydrate foods seem to enhance serotonin production and produce similar effects. "It is the balance between different neurotransmitters that helps regulate mood," Chudler says.
    Proper nutrition may also enhance brainpower. Choline is a substance similar to the B vitamins. It’s found in egg yolks, whole wheat, peanuts, milk, green peas, liver, beans, seafood, and soybeans. The brain uses it to make the neurotransmitter acetylcholine. To test the effects of choline on memory and learning, researchers at the Massachusetts Institute of Technology gave memory tests to college students before increasing the amount of choline in their subjects’ diets. Later, they retested. On the average, memories were better, and the students learned a list of unrelated words more easily.
When is depression resulted?
选项 A、When the level of serotonin is low.
B、When the level of serotonin is high.
C、When serotonin is released from neurons.
D、When people eat carbohydrate foods.
答案A
解析 第4段第5句末的similar effects指的是“同样可以使人不再情绪低落”，由此可见，本句指出了serotonin的含量高，情绪就不会低落，反过来说，serotonin的含量低就会导致情绪低落，这就是A的内容。C项具有干扰性，但原文并没有依据表明神经元细胞释放serotonin时人的情绪就会低落，故不选。
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