Past studies have shown that people's non-declarative memories, also known as "how to" memories, benefit from getting enough sleep, but the effect on declarative memories was unknown. Declarative memories are the memories of facts and events.
"We sought to explore whether sleep has any impact on memory consolidation," says lead researcher Dr. Jeffrey M. Ellenbogen.
The study, published in the July 11 issue of Current Biology, examined 60 people without sleep disorders or abnormal sleep patterns, and who did not use prescription drugs. The participants were divided into four groups. One group would sleep before testing, one would wake before testing, one would sleep before testing with interference, and the final group would wake before testing with interference.
"Interference is the concept in memory research that learning some new piece of information leads to the forgetting of something else, particularly when that something else is very similar," Ellenbogen said.
Study participants in the non-interference groups showed recall abilities that were slightly higher when compared to the wake group, and even the interference group that was allowed to sleep showed significantly better recall than the wake group.
"The benefit was even larger than we were anticipating." Ellenbogen said.
The scientists said the findings lead them to believe that sleep is imperative to the creation and preservation of memories, and that sufficient sleep is particularly important to people with mentally demanding lives, such as doctors and college students.