This post is also available in Dutch.
Sleep is an important part of life. It allows our bodies to recover as well as to process everything that happened during the day. It has also been shown to be vital to our memory: During sleep, information we gained and learned is transferred from short-term memory to long-term memory. This process is called consolidation.
Sleep on it
Past research has already proven what some high school teachers used to say: Study before you go to bed and you will remember better the next day. For young kids and adults alike, researchers have shown that sleep (or, more precisely, sleep consolidation) has a beneficial effect on remembering newly introduced words. Even very short naps, for example: only 6 minutes, seem to be enough to improve the recall of words.
A few years ago, scientists in Switzerland took further steps and investigated how memory was affected by listening to words while asleep. At the University of Zurich, they invited native German speakers into the lab and had them listen to the Dutch translations of 120 German words which were displayed on a screen. The participants were asked to memorise as many words as possible. Afterwards, they were divided into four groups: while some continued to listen to the translations awake, either occupied by another task or without distractions, another group just went to sleep. The last group could sleep as well, but they heard the Dutch translations again during sleep. Each time they entered the non-rapid eye-movement (non-REM) stage, the researcher re-played the words. The results show that the “only sleep” group performed better than the waking groups, confirming that sleep consolidation helps learning. However, the group who could also listen to the words during sleep outperformed them all.
Doing things in your sleep
Recently, scientists at the University of Bern discovered that, while asleep, our brains might be capable of more than only reinforcing what we just learned . We can also learn new things. In their study, the participants heard made-up words in combination with real German words. In each pair, the made-up word was heard first, followed by the German word. The words were names of objects that differed in size. After waking up, they had to perform a task that would gauge their knowledge of the made-up words: indicating the size of the object the word referred to.
In order to process new information and allow
this memory formation, the brain apparently needs to be in the so called
“slow-wave” phase of the non-REM sleep, which is known as deep sleep. When a
deep sleep phase preceded the German word of the pair, the association was most
likely to be learned.
This knowledge could open up all kinds of new ideas
and ways to learn new information. Hold your horses, however, before you race
off into dreamland listening to all of your study material. Further research on
this way of learning needs to be conducted before we know whether, for example,
it could affect sleep quality. But maybe listening to some vocabulary before
your next big trip could pay off.
 Sleep usually goes through two stages: rapid eye movement and non-rapid eye movement. The former is a more active stage during which we dream vividly, while the latter is more relaxed, showing calmer brain activity. We wrote about this a while back: http://blog.donders.ru.nl/?p=5649&lang=en.
Julia Egger is a PhD candidate at the Language Development Department of the Max Planck Institute for Psycholinguistics where she works on how the environment influences how children learn new words.