Remember when you were in high school or college, and faced with studying for a big test? At some point along the way, you probably heard the old theory that going to sleep with your textbook under your pillow would help you magically transfer the knowledge into your memory banks. Unfortunately, there is no evidence to support the magical transfer, but a new study, published in the journal Neurobiology of Learning and Memory, has established a correlation between sleeping and retaining learned information.
A research project at Saarland University in Germany has demonstrated that a short nap, lasting about an hour, can dramatically improve memory performance. Headed by Professor Axel Mecklinger and coordinated by graduate research student Sara Studte, the study examined 41 volunteers. The participants were asked to learn single words and word pairs. At the end of the learning phase, the participants were tested to see what information they retained. Then the group was divided roughly in half. The control group watched a DVD, while the other group were allowed to sleep. Afterward, the participants were all re-tested. The group that had taken a nap retained substantially more word pairs in memory than did the control group. Professor Mecklinger reported:
Even a short sleep lasting 45 to 60 minutes produces a five-fold improvement in information retrieval from memory.
The difference in the two groups was exhibited in the pre-nap and post-nap results. The group that slept for about an hour demonstrated the same memory performance after the nap as they did before the nap. The memory performance of the control group was significantly worse when tested after approximately an hour of watching the DVD.
The study focused on the role of the hippocampus, the portion of the brain in which memories are consolidated. The consolidation is the process through which previously learned information is transferred into storage in the long-term memory. The researchers explain:
We examined a particular type of brain activity, known as “sleep spindles,” that plays an important role in memory consolidation during sleep. [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.
The brain essentially gives learned information a label, to make it easier to retrieve that information at a later time. The study demonstrates the greater the number of sleep spindles that appear in the EEG, the stronger the person’s memory of information.
To ensure the validity of the study, the researchers gave the participants not only 90 single words, but also 120 word pairs which were essentially meaningless. A sample word pair cited by Dr. Mecklinger was “milk-taxi.” Because the participants have not seen these two words paired in other contexts, they cannot rely on memory clues. Participants must therefore access the specific memory of the learning episode in the hippocampus.
The researchers conclude:
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.
The same principle applies at home. We know challenging our brains to learn new information helps us stay mentally alert. Now we know taking a “power nap” supports our ability to retain new information.