Sleep aids memory. Whether tested in animals or humans, studies have shown that sense memories–such as learning a certain sequence of dance steps–take root more solidly when paired with adequate rest. Now new research shows that so-called declarative memories–such as a sequence of facts–also benefit from slumber, especially when subjects are challenged with subsequent, competing information.

Jeffrey Ellenbogen of Harvard Medical School and his colleagues recruited 60 healthy subjects–excluding night owls, the restless and the lethargic–and asked them to memorize 20 pairs of random words, such as blanket and village. The participants were assigned to one of five groups of 12 and had unlimited time to learn the pairings. Two of the groups began learning at 9 A.M and returned for testing at 9 P.M. that evening–with no naps allowed–and two of the groups began learning at 9 P.M. and returned for testing at 9 A.M. the following morning after a night’s sleep.

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