Swiss psychologists have found that listening to new languages
when asleep can actually help to reinforce learning.

The team from the Swiss National Science Foundation (SNSF) who
were writing for the journal Cerebal Cortex, carried out the
experiment on sixty German-speaking student volunteers. The
students were gathered together at 10pm in order to learn a
selection of Dutch words for the first time. Whilst half of the
students went to sleep under lab conditions, the other half were
instructed to stay awake. Both groups then had the Dutch words
played back to them.

After re-testing the students at approximately 2am, those who
had got some shut eye could remember the new words better than
those who were forced to stay awake.

EEG recordings, which measured the electrical activity in the
brain of those volunteers who slept, found that they had a higher
frequency of frontal slow waves as well as more activity in both
the right frontal and left parietal lobe of the brain, which is
responsible for processing new languages.

All in all this study proved that the brain takes in new
information more effectively whilst sleeping and is more likely to
remember information on awakening.