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For some time past it has been widely accepted that babies and other creatures learn to do things because certain acts lead to "rewards" , and there is no reason to doubt that this is true. But it used also to be widely believed that effective rewards, at least in the early stages, had to be directly related to such basic physiological " drives" as thirst or hunger. In other words, a baby would learn if he got food or drink, some sort of physical comfort, not otherwise. It is now clear that this is not so. Babies will learn to behave in ways that produce results in the world with no reward except the successful outcome. Papousek began his studies by using milk in the normal way to " reward" the babies and so teach them to carry out some simple movements, such as turning the head to one side or the other. Then he noticed that a baby who had had enough to drink would refuse the milk but would still go on making the learned response with clear signs of pleasure. So he began to study the children’’s response in situation where no milk was provided. He quickly found that children as young as four months would learn to turn their heads to right or left if the movement "switched on" a display of lights, and indeed that they were capable of learning quite complex turns to bring about this result, for instance, two left or two right, or even to make as many as three turns to one side. Papousek’’s light display was placed directly in front of the babies and he made the interesting observation that sometimes they would turn back to watch the lights closely although they would "smile and bubble" when the display came on. Papousek concluded that it was not primarily the sight of the lights that pleased them, it was the success they were achieving in solving the problem, in mastering the skill, and that there exists a fundamental human urge to make sense of the world and bring it under intentional control. According to Papousek, the pleasure babies get in achieving something is a reflection of________.
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Eat More, Weigh Less, Live Longer Clever genetic detective work may have found out the reason why a near-starvation diet prolongs the life of many animals. Ronald Kahn at Harvard Medical School in Boston, U.S., and his colleagues have been able to extend the lifespan (寿命) of mice by 18 per cent by blocking the rodent’s (啮齿动物) increase of fat in specific cells. This suggests that thinness--and not necessarily diet--promotes long life in "calorie (热量卡) restricted" animals. "It’s very cool work," says aging researcher Cynthia Kenyon of the University of California, San Francisco. "These mice eat all they want, lose weight and live longer. It’s like heaven." Calorie restriction dramatically extends the lifespan of organisms as different as worms and rodents. Whether this works in humans is still unknown partly because few people are willing to submit to such a strict diet. But many researchers hope they will be able to trigger the same effect with a drug once they understand how less food leads to a longer life. One theory is that eating less reduces the increase of harmful things that can damage cells. But Kahn’s team wondered whether the animals simply benefit by becoming thin. To find out, they used biology tricks to disrupt the insulin (胰岛素) receptor (受体) gene in lab mice, but only in their fat cells. "Since insulin is needed to help fat cells store fat, these animals were protected against becoming fat," explains Kahn. This slight genetic change in a single tissue had dramatic effects. By three months of age, Kahn’s modified mice had up to 70 per cent less body fat than normal control mice, despite the fact that they ate 55 per cent more food per gram of body weight. In addition, their lifespan increased. The average control mouse lived 753 days, while the thin rodents averaged a lifespan of 887 days. After three years, all the control mice had died, but one-quarter of the modified rodents were still alive. "That they get these effects by just manipulating the fat cells is controversial," says Leonard Guarente of the Massachusetts Institute of Technology, who studies calorie restriction and aging. But Guarente says Kahn has yet to prove that the same effect is responsible for increased lifespan in calorie-restricted animals. "It might be the same effect or there might be two routes to long life," he points out, "and that would be very interesting.\ What does the last sentence in the third paragraph imply
For some time past it has been widely accepted that babies and other creatures learn to do things because certain acts lead to "rewards" , and there is no reason to doubt that this is true. But it used also to be widely believed that effective rewards, at least in the early stages, had to be directly related to such basic physiological " drives" as thirst or hunger. In other words, a baby would learn if he got food or drink, some sort of physical comfort, not otherwise. It is now clear that this is not so. Babies will learn to behave in ways that produce results in the world with no reward except the successful outcome. Papousek began his studies by using milk in the normal way to " reward" the babies and so teach them to carry out some simple movements, such as turning the head to one side or the other. Then he noticed that a baby who had had enough to drink would refuse the milk but would still go on making the learned response with clear signs of pleasure. So he began to study the children’’s response in situation where no milk was provided. He quickly found that children as young as four months would learn to turn their heads to right or left if the movement "switched on" a display of lights, and indeed that they were capable of learning quite complex turns to bring about this result, for instance, two left or two right, or even to make as many as three turns to one side. Papousek’’s light display was placed directly in front of the babies and he made the interesting observation that sometimes they would turn back to watch the lights closely although they would "smile and bubble" when the display came on. Papousek concluded that it was not primarily the sight of the lights that pleased them, it was the success they were achieving in solving the problem, in mastering the skill, and that there exists a fundamental human urge to make sense of the world and bring it under intentional control. In Papousek’’s experiment babies make learned movements of the head in order to________.
Human Heart Can Make New Cells Solving a longstanding mystery, scientists have found that the human heart continues to generate new cardiac cells throughout the life span, although the rate of new cell production slows with age. The finding, published in the April 3 issue of Science, could open a new path for the treatment of heart diseases such as heart failure and heart attack, experts say. "We find that the beating cells in the heart, cardiomyocytes, are renewed," said lead researcher Dr. Jonas Frisen, a professor of stem cell research at the Karolinska Institute in Stockholm, Sweden. "It has previously not been known whether we were limited to the cardiomyocytes we are born with or if they could be renewed," he said. The process of renewing these ceils changes over time, Frisen added. In a 20-year-old, about 1 percent of cardiomyocytes are exchanged each year, but the turnover rate decreases with age to only 0.45 percent by age 75. "If we can understand how the generation of new cardiomyocytes is regulated, it may potentially possible to develop pharmaceuticals that promote this process to stimulate regeneration after, for example, a heart attack," Frisen said. That could lead to treatment that helps restore damaged hearts. "A lot of people suffer from chronic heart failure," noted co-author Dr. Ratan Bhardwaj, also from the Karolinska Institute. "Chronic heart failure arises from heart cells dying," he said. With this finding, scientists are "opening the door to potential therapies to having ourselves heal ourselves," Bhardwaj said. "Maybe one could devise a pharmaceutical agent that would make heart cells make new and more cells to overcome the problem they are facing." But barriers remain. According to Bhardwaj, scientists do not yet know how to increase heart cell production to a rate that would replace cells faster than they are dying off, especially in older patients with heart failure. In addition, the number of new cells the heart produces was estimated using healthy hearts--whether the rate of cell turnover in diseased hearts is the same remains unknown. The human heart stops producing cardiac cells ______.
How much did the man spend on clothes
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