Generations of school students have gone to bed the night before a test with their class notes tucked under their pillow, hoping the knowledge would somehow be magically transferred into their brains while they slept.
That they were not completely taken in by a superstitious belief has now been demonstrated by a team of neuropsychologists, who have shown that even a brief sleep can significantly improve retention of learned material in memory.
Even an hour of sleep can help memory
Sara Studte, a graduate biologist specializing in neuropsychology at Saarland University in Germany, working with her PhD supervisor Axel Mecklinger and co-researcher Emma Bridger, examined how power naps influence memory performance.
The results are clear: “Even a short sleep lasting 45 to 60 minutes produces a five-fold improvement in information retrieval from memory,” says Mecklinger.
Strictly speaking, memory performance did not improve in the nap group relative to the levels measured immediately after the learning phase, but they did remain constant.
“The control group, whose members watched DVDs while the other group slept, performed significantly worse than the nap group when it came to remembering the word pairs,” says Professor Mecklinger. “The memory performance of the participants who had a power nap was just as good as it was before sleeping, that is, immediately after completing the learning phase.”
Examining the hippocampus
The researchers were particularly focused on the role of the hippocampus — a region of the brain in which memories are ‘consolidated’ — the process by which previously learned information is transferred into long-term memory storage.
“We examined a particular type of brain activity, known as ‘sleep spindles,’ that plays an important role in memory consolidation during sleep,” says Studte.
A sleep spindle is a short burst of rapid oscillations in the electroencephalogram (EEG). “We suspect that certain types of memory content, particularly information that was previously tagged, is preferentially consolidated during this type of brain activity,” says Mecklinger. Newly-learned information is effectively given a label, making it easier to recall that information at some later time. In short, a person’s memory of something is stronger, the greater the number of sleep spindles appearing in the EEG.
In order to exclude the possibility that the participants only recall the learned items due to a feeling of familiarity, the researchers used the following trick: the test subjects were required to learn not only 90 single words, but also 120 word pairs, where the word pairs were essentially meaningless.
Axel Mecklinger explains, “A word pair might, for example, be ‘milk-taxi.’ Familiarity is of no use here when participants try to remember this word pair, because they have never heard this particular word combination before and it is essentially without meaning. They therefore need to access the specific memory of the corresponding episode in the hippocampus.”
The research teams draws a clear conclusion from its study: “A short nap at the office or in school is enough to significantly improve learning success. Wherever people are in a learning environment, we should think seriously about the positive effects of sleep,”says Axel Mecklinger.