Scientists have discovered the clearest evidence yet that REM sleep is critical for memory.
Researchers, writing in the journal Science, said they had found that disrupting brain activity in sleeping mice can stop the animals remembering things they learned that day.
According to the study the researchers found that by switching off certain brain cells they could silence a particular, rhythmic type of brain function – without waking the mice.
If they did this during REM sleep, the mice failed subsequent memory tests.
REM sleep in humans is when dreams take place but it has been unknown as to whether this phase of sleep is important for cementing memory.
It is a type of sleep seen across the animal kingdom including in birds and lizards.