The REM sleep - Memory consolidation hypothesis

It has been hypothesized that REM (rapid eye movement) steep has an important role in memory consolidation. The evidence for this hypothesis is reviewed and found to be weak and contradictory. Animal studies correlating changes in REM steep parameters with learning have produced inconsistent results and are confounded by stress effects. Humans with pharmacological and brain lesion-induced suppression of REM steep do not show memory deficits, and other human steep-learning studies have not produced consistent results. The time spent in REM steep is not correlated with learning ability across humans, nor is there a positive relation between REM steep time or intensity and encephalization across species. Although steep is clearly important for optimum acquisition and performance of learned tasks, a major role in memory consolidation is unproven.