你是不是总觉得自己老了,头脑不够用了 | 经济学人
本文音频及原文摘自杂志The Economist2017年第2期，Special Report。
Old dogs, new tricks[0]
As people age, the brain changes in both good ways and bad
IF YOU ARE over 20, look away now. Your cognitive performance[认知能力] is probably already on the wane[1]. The speed with which people can process information declines at a steady rate from as early as their 20s.
A common test of processing speed is the "digit symbol substitution test", in which a range of symbols are paired with a set of numbers in a code. Participants are shown the code, given a row of symbols and then asked to write down the corresponding number in the box below within a set period. There is nothing cognitively[感知地;认知地] challenging about the task; levels of education make no difference to performance. But age does. Speed consistently declines as people get older.
LR注：digit symbol substitution test(数字符号替换测试) 类似下图这样的测试。
（图片来源于网络）
Why this should be is still a matter of hypothesis, but a range of tentative[2] explanations has been put forward. One points the finger at myelin[3], a white, fatty substance that coats axons[轴突], the tendrils[卷须] that carry signals from one neuron to another.
Steady reductions in myelin as people age may be slowing down these connections. Another possibility, says Timothy Salthouse, director of the Cognitive Ageing Laboratory at the University of Virginia, is depletion[4] of a chemical called dopamine['dəʊpəmiːn][多巴胺], receptor sites[受体部位] for which decline in number with advancing age.
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注释
[0]Old dogs,new tricks源于You can't teach an old dog new tricks：said to mean that it is very difficult to teach someone new skills or to change someone's habits or character 年老难学艺；本性难移
[1]on the wane:becoming less strong, powerful, popular, etc. （权力、人气等）衰落，减弱
There are signs that support for the group is on the wane.
有迹象表明该党的支持率正日益下降。
[2]tentative:(of a plan or idea) not certain or agreed, or (of a suggestion or action) said or done in a careful but uncertain way because you do not know if you are right （计划、想法、建议、行动等）试验（性）的，试探（性）的，暂时的
I have tentative plans to take a trip to Seattle in July.
我暂定7月份去西雅图旅行。
[3]myelin ['maɪəlɪn]
a substance containing a lot of fat that forms a covering around nerves, especially those in the brain, protecting them and helping them to send signals effectively 髓磷脂（含大量脂肪，特别是在脑神经周围形成保护层，保障脑神经有效发出信号）
The myelin sheath around the neuron is damaged.
神经元周围的髓鞘遭到破坏。
[4]depletion:a reduction in something 减少；减小；缩小
the depletion of the ozone layer
臭氧层变薄
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Fortunately, there is some good news to go with the bad. Psychologists distinguish between "fluid intelligence[5]", which is the ability to solve new problems, and "crystallised intelligence[5]", which roughly equates to[同等看待;使相等] an individual's stock of accumulated knowledge.
These reserves of knowledge continue to increase with age: people's performance on vocabulary and general-knowledge tests keeps improving into their 70s. And experience can often compensate for cognitive decline. In an old but instructive study of typists[打字员] ranging in age from 19 to 72, older workers typed just as fast as younger ones, even though their tapping speed was slower. They achieved this by looking further ahead in the text, which allowed them to keep going more smoothly.
What does all this mean for a lifetime of continuous learning[终身学习,持续学习]? It is encouraging so long as people are learning new tricks in familiar fields. "If learning can be assimilated[6] into an existing knowledge base, advantage tilts[7] to the old," says Mr Salthouse. But moving older workers into an entirely new area of knowledge is less likely to go well.
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注释
[5]流体智力（Fluid Intelligence）是一种以生理为基础的认知能力，如知觉、记忆、运算速度、推理能力等。流体智力是与晶体智力相对应的概念，流体智力随年龄的老化而减退。
而晶体智力（Crystallised intelligence）则并不随年龄的老化而减退，晶体智力主要指学会的技能、语言文字能力、判断力、联想力等。
[6]assimilate:to become part of a group, country, society, etc., or to make someone or something become part of a group, country, society, etc. 吸收；融入；加入；（使）同化
The European Union should remain flexible enough to assimilate more countries quickly.
欧盟应该保持足够的灵活性，以加快步伐吸收更多的国家为其成员。
[7]tilt:to (cause to) move into a sloping position （使）倾斜
He tilted his chair backwards and put his feet up on his desk.
他把椅子向后倾，双脚搁在写字台上。
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以上言论不代表本人立场。
原文摘自The economist，仅外语学习之用。
其中生词解释来源于Cambridge Dictionaries
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