2010考研英語：歷年真題來源報刊閱讀100篇(39)

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　　Can milk make you happy?

　　Can fish make you smart?

　　Imagine yourself lying in bed, your mind in turmoil. You toss and turn, but sleep won't come. Maybe a bedtime snack would help. What should you choose? If you think first of toaster waffles or popcorn, some experts would say you're on the right track. Foods high in complex carbohydrates-such as cereals, potatoes, pasta, crackers, or rice cakes-make many people relaxed and drowsy.

　　Missed that one? Try again. Suppose the weather's rotten, you forgot your homework, and your best friend's mad at you. What's good medicine when you're feeling low? A sugary cola or candy may give you a quick lift, but you'll crash just as quickly. Better choices may be Brazil nuts (for selenium), skim milk (for calcium), or a spinach salad (for folic acid). In research studies, all three of those nutrients have been shown to lift spirits and battle the blues.

　　Try one more. You have a math test coming up in the afternoon. You want to be sharp, but you usually feel sleepy after lunch. Is your best choice an energy fix of fries and a shake or a broiled chicken breast and low-fat yogurt? If you pick the high-fat fries and shake, you may feel sluggish and blow that test. The protein-rich chicken and yogurt are better choices. Protein foods energize, some experts say.

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

　　考研詞匯：

　　drowsy[ˈdrauzi]

　　a.昏昏欲睡的, 催眠的, (街、市等)沉寂的