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Selective Memory Erasure选择性记忆删除 Ya?l: Have any unpleasant memories, Don? Don: Sure. Who doesnt? Y: What would you say to having them permanently?erased?from your brain? D: Without losing other memories? Y: Right. Scientists did just that with rats. They trained rats to fear two different sounds by sending a mild electric shock through the rats paws when they played the sounds. This Pavlovian technique resulted in the rats freezing up in nervous??anticipation?of the shocks every time they heard either sound. Scientists wanted to know whether they could?erase?one of the memories without erasing the other one, even though both sounds result in the same fear. D: I didnt know scientists knew how to?erase?memories at all. Y: They do. You see, long-term memories arent nearly as?solid?as we like to think. Theyre actually very?fragile. Every time we recall a long-term memory, it becomes?malleable. Just before playing one of the sounds, scientists injected half the rats with a chemical that interferes with memory reconsolidation. Thus, when they were in the process of remembering what accompanies the sound, the drug went to work. D: Then what? Y: When they played both sounds a day later, the rats that had been injected with the chemical did not freeze up when they heard the sound that had accompanied the drug. They froze as usual when they heard the second sound. D: They had forgotten to be afraid. Hmm. This business makes me kind of nervous. Y: I know what you mean, but for people with?post-traumatic?stress disorder, selective memory erasure could prove enormously useful. D: True. I guess some fears are best laid to rest. Y: 你有过不愉快的记忆吗，唐？ D: 当然有，每个人都有的。 Y: 如果把它们永远从你的大脑里删除，你觉得怎么样？ D: 不丧失其他记忆？ Y: 是的。科学家们用老鼠做了实验。他们先训练老鼠对两种不同的声音产生恐惧。当他们播放声音的时候轻度电击老鼠的爪子。这种巴普洛夫技术产生了这种结果：每次老鼠听到其中一种声音就会怕被电击而变得非常紧张。科学家想知道他们能否将删除老鼠对其中一种声音的恐惧，而且要保留另外一组记忆。尽管两种声音都会让老鼠产生恐惧。 D: 我不知道科学家们如何删除记忆。 Y: 他们可以的。要知道，长期性记忆并非我们想象的那么牢固。实际上它们是很容易被破坏的。每当我们回忆起一段长期记忆，它都是具有可塑性的。在播放声音之前，科学家先给老鼠注射一种干扰再次巩固记忆的药物。因此，当它们在回忆声音的过程