If you put your history notes under your pillow and sleep on them the night before an exam, will you do any better on the test? Most of us have held out hope this might help, but alas, knowledge can’t seep through the pillow into the 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 soak up things during slumber. Consider the following:

Foreign words

In one experiment, researchers gave native German speakers some basic Dutch vocabulary words. Afterwards, they played words for some study participants while they slept, without the participants' knowledge. The volume was set low so it didn’t wake them up, and only the newly introduced words were used.

Other study participants listened to the same words while they were awake, but those who heard the words in their sleep were better able to identify and translate them later. This was true only for the specific words that were played while they slept. Another group listened to words while they walked; the walkers did not have the same success remembering the words as the sleeping group.

When the EEGs of the sleeping learners were evaluated, they revealed that those participants had more slow-wave brain activity throughout the night; more slow waves, they concluded, resulted in better retention of the new words.

Musical melodies

Having trouble learning a new melody? Listening to it while you sleep could do the trick. In another sleep-and-learning study, researchers had a group of subjects learn a guitar melody from a play-along video lesson; then the participants took a nap.

What the volunteers didn’t know was that some of them were treated to recordings of the melody they had just learned while they were asleep. As you can probably guess, those who heard it while napping were able to play the tune far better than those who didn’t hear it.

Memories

Well, you don’t exactly learn memories when you sleep, but one group of researchers found that you can make memories stick during slumber. As Business Insider explains, our brains use a special “tagging system” to distinguish between important experiences and insignificant ones. The important events go to long-term memory storage, while the inconsequential ones are left in a waiting area, where they are eventually replaced by new ones.

But two studies around memory found that using sound or smell can help people have a better grasp of their memories, even insignificant ones. In one study, participants heard specific sounds when they were arranging icons on a computer. While the subjects slept, the researchers played a selection of the sounds to some of the participants. The group who heard the sounds were not only better able to recall the specific objects associated with the sounds that were played, but all of the items.

In the odor study, a similar approach was used by employing smell instead of sound. When people were exposed to the scent of rose while learning something, they remembered it better when they were given the same whiffs during sleep.

And with this in mind, Natalie Wolchover of Life's Little Mysteries recommends the following technique: study a foreign language vocabulary list while sitting next to a rosemary plant, and then put the plant on your bedside table for the night, the smell of rosemary may influence your brain to spend more time strengthening the memories of the vocabulary than it otherwise would. 

Maybe nocturnal help with the history exam isn't such a stretch after all.

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