The REM sleep-memory consolidation hypothesis

Abstract

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

Fig. 1.

Sleep durations in representative mammals. Daily REM sleep time in mammals does not positively correlate with encephalization. The highest levels of REM sleep are seen in the platypus and the lowest in the dolphin. Despite our unique learning capabilities, human REM and non-REM sleep parameters are not unusual and are in accord with our size and level of maturity at birth relative to other mammalian species. Number of hours of REM sleep and total sleep across the 24-hour cycle are listed for each animal pictured (36, 37). [Photo credits: platypus, Tom McHugh/Photo Researchers; opossum (photo is of a Virginia opossum), Alden M. Johnson, California Academy of Sciences; ferret (photo is of a black-footed ferret), © D. Robert Franz/CORBIS; big brown bat, © 1997 Merlin Tuttle, from Bats: Shadows in the Night, used by permission of Crown Children’s Books; hedgehog, Maurizio Lanini/CORBIS; armadillo, John and Karen Hollings-worth/U.S. Fish and Wildlife Service; human, Kristi Alderman; guinea pig, Animals Animals; guinea baboon, Mickey Gibson/Animals Animals; sheep, Barbara Wright/Animals Animals; horse, Lucie R. Alderman; giraffe, Arthur J. Emmrich, California Academy of Sciences; dolphin, Gerard Lacz/Animals Animals]