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    If you put your history notes under your pillow (枕头) and sleep on them the night before an exam, will you do any better on the test? Most of us have hoped this might help. However, _______ can't go through the pillow into your brain. But that doesn't mean you can't learn while you sleep.  

    Scientists aren't exactly sure how it works, but they have discovered that the brain can learn things during sleeping hours.

    In one experiment(实验), researchers gave German speakers some Dutch words to learn. Then, they divided them into three groups. The researchers played Dutch words for people in Group 1 while they slept, without telling these German speakers what they were doing. The sound was low so it didn't wake them up, and only the newly introduced words were used.

    Another group listened to the same words while they were awake. The researchers found the people in Group 1 were better able to identify(确认) and translate the words later. This was true only for the words that were played while they slept. The third group listened to words while they walked. The walkers did not have the same success remembering the words as the sleeping group.

    The researchers later found that people had more slow-wave(慢波的) brain activity throughout the night. They said that more slow waves made people have better memory for the new words.