Think back to a really vivid memory. Got it? Now try to remember what you had for lunch three weeks ago. That second memory probably isn’t as strong—but why not? Why do we remember some things and not others? And why do memories eventually fade?

回想一个非常生动的记忆。明白了吗？现在试着回想一下三周前的午餐吃了什么。第二种记忆可能没有那么强烈--但为什么不呢？为什么我们会记得一些事情，而不是其他事情？又为什么记忆最终会消失？