Sleep and learning

Many competing theories have been advanced to discover the possible connections between sleep and learning in humans. One theory is that sleep consolidates and optimizes the layout of memories, though recent evidence suggests this may be restricted to explict procedural memories [1].

Increased learning
Popular sayings such as "sleep on it" or "consult the pillow" reflect the theory that remolded memories produce new creative associations in the morning. Many studies demonstrate that a healthy sleep produces a significant learning performance boost. Healthy sleep must include the appropriate sequence and proportion of NREM and REM phases, which play a different role in memory consolidation-optimization process.

A study [2] has also found that after sleep there is an increased insight, that is, a sudden gain of explicit knowledge. Thus during sleep the representation of new memories are restructured.

Other theories
Other researchers' theories on additional functions of sleep differ significantly. One older idea is the energy conservation theory. Others claim that REM sleep is needed to "refresh" the brain after NREM phase, or that REM is needed to prevent stasis of fluids in the eye.