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You may not be able to unlock all the secrets of the universe while you snooze, but it's still possible to reinforce what you've already learned.

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[INTRO ♪].

We've probably all done this at some point in our lives: it's the night before a big exam, and … you haven't started studying yet. You'll just have to cram as much information as possible into your brain in one night and hope you remember it tomorrow.

Wouldn't it be nice if you could just go to sleep, have a recording of everything you need to know playing in the background, and wake up ready for the test? Unfortunately for those of us who are chronic procrastinators, that doesn't work. You can't learn new information while you sleep.

But it turns out that you can boost your recall of what you studied while you were awake. The idea that you can learn totally new information while you sleep has been debunked for a long time. Way back in 1955, researchers showed pretty conclusively that it doesn't work.

Earlier studies had suggested that people could learn new things just by hearing them in their sleep, but there were problems with the methods used in those studies, so the team wanted to look into it more closely. Using an EEG, which measures brain activity, to monitor how deeply asleep the subjects were, they found that people were only able to remember the information played to them if they heard it when they were in the lighter stages of sleep. The … really, really light stages.

So light, in fact, that the participants were actually mostly awake. 62 years later, that study's conclusions still stand: there's no good evidence that you can learn totally new information in your sleep. But scientists have found that there might be a way to boost the part of the learning process that happens during sleep. Sleep plays a vital role in how you create and store memories.

While you're awake, you learn all sorts of new stuff, taking in facts and experiences just from going about your everyday life. That's when your brain encodes memories, making new connections between neurons so you can remember it all later. Then, when you go to sleep, your brain goes through the consolidation phase of memory formation.

Scientists aren't totally sure how that works, but they think your brain turns all that stuff you just learned into solid, long term memories by reactivating them and strengthening those new connections. And recent research has found that there are ways to kind of hack that process. In a 2007 study, for example, a group of neuroscientists had people learn the locations of a bunch of different objects while it smelled like roses, then made it smell like roses again while they were asleep.

When they woke up, the subjects were better at remembering where the objects were, compared to when they did the same task without any smells. The researchers proposed that when the subjects smelled roses while they slept, that boosted the memory consolidation process because their brains associated the smell with the memories of the object locations. Basically, the smell acted as a cue to their brains to reactivate those memories, strengthening the connections between the neurons that stored them.

And stronger connections meant they had an easier time recalling the memories when they woke up. That 2007 study was small, but later studies that tested the idea found similar results. And other research has found that this works with more than just odor cues.

You can do it with sound, too. For example, in a study published in The Journal of Neuroscience in 2013, 60 people were asked to place 72 images in different locations on a computer screen. Each time they placed an item, a corresponding sound was played— so for example, if they were placing down a picture of a cat, they'd hear a meow.

They were told that remembering each of these items later on would earn them a certain number of points. Half of the items had super high point values, and half were super low. But to get the most points possible, they had to remember where they placed absolutely everything.

And with 72 items, that wouldn't be easy. After they'd made their placements, the subjects took a 90 minute nap— just about enough for one full cycle of sleep. While the people in the experimental group were sleeping, they were played 18 of the sounds associated with low value items.

The people in the control group just slept with white noise playing instead. Once they were wide awake and trying to remember the locations of as many items as they could for those sweet, sweet science points, the subjects mostly remembered the ones with high point values. But the people in the experimental group also tended to remember the low-value items—the ones they'd been reminded of while they slept.

The researchers concluded that, just like in the studies on odor cues, the sounds cued the subjects' brains to reactivate the memories associated with them. That strengthened those memories, so they were better at recalling them later. And, again like with odor cues, other studies have also found that sound cues can boost your recall.

For example, in a 2014 study that involved 68 subjects, a group of researchers found that playing sound cues while people were asleep helped them learn a new language. They had people learn 120 new words and their translations, then played some of those new words back to them while they slept. The team found that people were able to remember about 10% more of the cued words than the words they hadn't heard while they were asleep.

But, in a follow-up study published the next year, the same group of researchers found that if they played the new words and their translations, the memory boost went away. So, it wasn't hearing the information while they slept that helped them remember it. It was the sound they associated with the memory.

When they heard the word and its translation, it became more than a simple sound cue, and the second word interfered with the memory consolidation process. So the next time you're cramming for a test, you might want to try connecting the new information with certain sounds or smells, then letting yourself hear or smell those things again when you go to sleep. You still might not do as well as you would have if you'd just studied properly, but hacking your memory could help you get a few more questions right.

Good luck! Thanks for watching this episode of SciShow Psych! If you want to learn more cool stuff like this about our weird human brains, you can go to and subscribe. [OUTRO ♪].