When you go to bed tonight, put the book under your pillow. Waking up tomorrow morning, you can remember everything that is written in it.
Remember this advice from your student days? Unfortunately, it doesn't work if you want to learn something new.
But don't give up hope. It turns out there are actually things you can learn, or at least improve your understanding, while you sleep. Most of them depend on one thing - sound.
Here are some skills you can improve while sleeping.
Foreign words
In a new experiment, native speakers of German started learning Dutch, starting with a basic vocabulary. Then they went to bed.
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Unbeknownst to the participants in the experiment, while they slept, some basic words for one group were played. The control group was not exposed to this effect. Later, when scientists had to pass tests on these words, the group that listened to them at night was able to better identify and translate them.
To make sure that the conclusions were tied to sleep (and not the result of the fact that this group additionally listened to words), members of another group listened to their recording while they were busy with something else during waking, to for example, walking. The results showed that they could not remember new words as well as those people who slept while listening.
Musical skills
In another experiment, researchers taught a group of people to play tunes on a guitar using a technique from the video game Guitar Hero. After that, all the volunteers went to bed. After waking up, everyone was asked to play again.
Unbeknownst to the sleeping participants, the same melody that they had just learned was played for one group. The other group was the control group. Volunteers who were played a sound while they slept, even if they had no memory of it, played a melody much better than those who did not hear it during sleep.
Where did you leave anything
In a 2013 study, scientists asked 60 people to use a computer to move a virtual object to a specific location on the screen. At this time a certain melody was played to them. Then two experiments were conducted during which the participants had to sleep. During the first experiment, they slept as usual, without playing any sounds. During the second, the melody that was played when they placed the object was played again, although none of the participants remembered hearing it.
Not surprisingly, after sleep, people's memory faded. But their memories were less lost when they heard - even unconsciously - the melody that played as they placed the object. Interestingly, their memories were sharper when participants were additionally told that the virtual object was of great importance.
How to protect special memories
Scientists believe that our brains use a special labeling system to separate critical memories from less important ones. As a result, the former fall directly into our long-term memory, while the less important are replaced by new ones.
But scientists believe there is a way to "hack" the system in our favor.
In a recent study, they found that people who listened to a memory-related sound - even a nonessential one - were able to retain it much better.
First, they worked with a group of volunteers to place icons on a computer screen in a specific location. The computer was programmed to play a specific sound as each object moved. When placing a cat icon, for example, a meowing sound was played; the placement of the bell icon was accompanied by a ringing sound. The researchers then allowed the participants to sleep. While one group slept, the scientists played the sounds of some of the icons. The other group heard nothing.
People who listened to any of the sounds were able to remember all objects better. Even one sound helped to evoke multiple memories.
What happens while we sleep, and is it good for our brain?
Our brain activity slows down during the night, but some of us spend more time in a special phase called slow sleep than others.
Scientists believe that slow-wave sleep is the phase during which some of our short-term memories are transferred to long-term storage in our prefrontal cortex.
In some experiments in which the researchers were able to study the brain wave activity of sleeping volunteers, they noticed that those who were exposed to sound at night (be it the German words that were played during the first study, or the guitar melody in the second experiment) also had a longer phase of slow sleep.
In other words, perhaps the more slow-wave sleep we get, the better, in the first place, for learning new skills and retaining important memories.