Scientists say a bursts of brain waves called sleep spindles may network between important regions of the brain to clear a path to learning.
They say this spindle driven networking is most likely to occur during stage 2 of non-REM sleep. That tends to happen before the deepest sleep.
Scientists say stage 2 non-REM sleep can account for half of a person's sleep and usually occurs in the second half of the night. That's why sleeping six hours or less may be short-changing yourself.