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.
The sleepers barely outperformed their sleepless peers in the first comparison: sleepers accurately recalled 94 percent of the pairings compared to just 82 percent for their peers. But when the researchers added a twist--forcing subjects in two of the groups to learn a new set of word pairs 12 minutes prior to testing--the well-rested radically outperformed the sleepy; sleepers recalled 76 percent of the initial pairs compared to just 32 percent for their peers who had gone without shut-eye. "Memories after sleep are resilient to disruption," the researchers conclude in the paper outlining the finding published yesterday in Current Biology.
Ellenbogen and his colleagues also attempted to control for concerns that the time of day might account for the finding. After all, many people perform at their best in the morning. The fifth group of 12 subjects learned the 20 word pairs at 9 P.M. one day and returned for testing as well as interference from a new set of words at 9 P.M. the following day. This group did almost as well as the original sleepers, recalling 71 percent of the original word pairs. In conjunction with animal studies that show such memories are replayed in the brain during rest, the researchers argue that sleep "orchestrates the strengthening of memories and thereby renders them less vulnerable to interference." Sleeping on it may just be the best way to remember something.