Expounding on their hypothesis that sleep is needed to clear the brain's short-term memory storage and make room for new information, Matthew Walker, from University of California/Berkeley (California, USA), and colleagues have found that an hour-long nap in the early afternoon can improve the capacity to learn.  The team recruited 39 healthy young adults and randomly assigned them to take a 90-minute early afternoon nap, or stay awake for the same duration Whereas both groups performed at comparable levels on a learning task completed prior to the nap time, another mental challenge after the naptime was completed markedly better by those who napped than those who stayed awake.   The findings support the notion that fact-based memories are temporarily stored in the hippocampus before being sent to the brain's prefrontal cortex, but this memory transfer is optimized with Stage 2 non-REM sleep.