We know that sleep strengthens memory. Logging rest, particularly slow-wave sleep, helps convert new information and experiences into long-term recollections through a process called consolidation. Now, a new study, published in the journal eLife, suggests that consolidation happens not only during your nightly #hardeight, but also during those shorter respites from consciousness we call naps. The napping brain, however, doesn’t treat all information equally, according to the study press release. Rather, it prioritizes information associated with reward processing.
In the study, 31 volunteers were randomly divided into “sleep” and “wake” groups and told to review eight pairs of pictures. While they were supposed to commit all eight pairs to memory, researchers promised a higher reward for remembering four of the pairs. After viewing the photos, volunteers took a 90-minute nap, during which time the “sleep” group napped and the wake group relaxed. Then, researchers tested volunteers’ photo memory and asked them to rate their confidence with respect to accurate recall. Three months later, researchers surprised volunteers with a repeat photo quiz and confidence rating. During both tests, volunteers simultaneously underwent hippocampal brain scans. Previous neuroimaging work has shown slow spindles, which are deep brain oscillations linked to memory consolidation, erupt in the hippocampus region during sleep.
During the initial quiz, both groups recollected the four pairs of high-reward photos equally well. But, the sleep group came out ahead at the three-month follow up, demonstrating sharper recall where it counted and reporting higher confidence ratings.
The sleep group also exhibited more hyped-up hippocampuses from the get-go. During the first test, regional activity was higher, but during the second test, researchers also saw increased connectivity between the hippocampus and two brain regions, the medial prefrontal cortex and striatum, which are involved in memory consolidation.
Together, photo-recall test results and neuroimaging scans suggest that the brain prioritizes memorizing information with a higher reward potential. The subsequent naps, for volunteers who got them, seem to have sealed in the high-priority info and shipped it off to the relevant brain regions for long-term storage. Three months later, the info remained safely tucked away in storage, available for use.
The study helps us better understand the brain as an efficient and discriminating information-absorbing machine, and further clarifies the role of sleep in aiding that process. So, the takeway seems obvious: Go memorize a bunch of photos for no particular reason. Then sleep on it. Send yourself a calendar invite for a re-test in early 2016. Make your friend do the same without that nap. Feel superior. Or just be sure to steal a quick nap during a study break to solidify the facts.