Listening to other languages while you sleep help reinforce learning, a team of Swiss psychologists has found.

Writing in the journal Cerebral Cortex, a team from the Swiss National Science Foundation (SNSF) led by biopsychologist Björn Rasch explains how the technique helps reactivate memories in order to consolidate them.

"Here, we tested for the first time whether verbal cueing during sleep can improve vocabulary learning."

Sixty German-speaking student volunteers were asked to sit and learn a series of Dutch words for the first time at around 10pm. Half were asked to then go to sleep, still under lab conditions, while the other half had to stay up. While the former were in non-rapid eye movement sleep, those same words they learned at 10pm were played back to them. The other group also had the words played back to them while they were awake.

The sleep deprived stayed up, and at 2am the sleeping group were woken and everyone was tested on the same group of words. Despite only hearing the Dutch words in their sleep, the students that got some shut eye could remember the German translation better than the group forced to stay awake. In fact the playback appeared to have no effect on those that were up all night. "Verbal cueing failed to improve memory during active and passive waking," write the authors.

It is, of course, entirely reasonable to assume that sleep depravation versus rest played a part in the results. However, the team accounted for this by also taking EEG recordings -- they measured the electrical activity in the brain as the volunteers listened back to the recordings while they slept. They found there was "a pronounced frontal negativity in event-related potentials, a higher frequency of frontal slow waves as well as a cueing-related increase in right frontal and left parietal oscillatory theta power". The latter is a particular indication of correlation, since the parietal lobe is responsible for integrating sensory information and also processing language. Theta oscillations, a type of EEG feedback, are associated with memory encoding when people are awake. It suggests the same thing happens when we're sleeping, or at least helps strengthen the original memory.

"Our method is easy to use in daily life and can be adopted by anyone," said Rasch.

For decades people have attempted to squeeze in knowledge while they sleep, hoping that through subliminal communication they can up their IQ or change their behaviour just by pressing play and having a nap. But there is more and more evidence to suggest this could be the case one-day.

A study by Northwestern University in Illinois published in 2009 showed that when a group of volunteers were taught to associate memories with sounds, when those sounds were later played back to them during the night the memories were consolidated. Then in 2012, neurobiologists from the Weizmann Institute of Science in Israel found that they could actually teach people to associate smells with sounds by conditioning them while they slept. It suggests we can actually learn entirely new things while we're sleeping, not just consolidate old memories. 

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