How to 'Cram' While Sleeping

Falling asleep is a gradual process.
Falling asleep is a gradual process. (Image credit: Image via Shutterstock)

Forget pulling all-nighters: There's a more restive way to cram for tests. New research by neuroscientists at Northwestern University in Chicago shows people can actually learn while they're asleep. How?

The trick is coaxing your unconscious brain to speed-build a set of memories — whatever it is you need to memorize in a hurry — instead of slowly cementing the memories over the course of months, as it normally would.

In the new study, published online June 24 in the journal Nature Neuroscience, study participants were given diagrams that showed them how to play two simple piano melodies, each 12 notes long. They spent an equal amount of time practicing playing each tune, then took a 90-minute nap. While they slept, one of the melodies was quietly played on repeat for four minutes. As a result, upon awakening, the study participants could accurately play the cued melody 4 percent more often than the melody that was not played while they slept — a significant memory boost, considering it resulted from just four minutes of "sleep-learning."

"The re-activation process in the experiment is thought to affect a naturally occurring memory consolidation process that normally proceeds over months (possibly years)," said Paul Reber, a psychologist at Northwestern and co-author of the study. [How Do We Fall Asleep?]

EEG scans of the sleeping study participants' brains revealed spindle activity — a type of brain wave thought to be associated with memory processing — in the part of their brains associated with hand motor skills and song learning in songbirds and humans. The more time the sleepers spent in the slow-wave sleep stage during which they exhibited this spindle activity, the bigger the difference between their accuracy playing the cued tune and the uncued tune. This suggests the cuing was influencing that memory consolidation process during slow-wave sleep.

So, besides piano songs, what kinds of information can you "cram" while asleep?

Clearly, resting your textbook near your dreaming head won't do any good. "As long as the memory is tied to a specific type of sound, it looks like the sound can re-activate and strengthen the previously learned information," Reber told Life's Little Mysteries. "It is possible this effect would help with strengthening memories from a classroom or lecture and that it could even help speed up second-language learning."

In other words, if you're learning a foreign language, it may help to play recordings of the language while you sleep. If you need to memorize information presented in a classroom lecture, it might also help to record the lecture and play it quietly at night.

Past research has shown this same memory consolidation process can be triggered by smells, too. If you study a Spanish vocabulary list while sitting next to a rosemary plant, and then put the plant on your bedside table for the night, the smell of rosemary may influence your brain to spend more time strengthening the memories of the Spanish vocabulary than it otherwise would.

Follow Natalie Wolchover on Twitter @nattyover. Follow Life's Little Mysteries on Twitter @llmysteries. We're also on Facebook & Google+.

Natalie Wolchover

Natalie Wolchover was a staff writer for Live Science from 2010 to 2012 and is currently a senior physics writer and editor for Quanta Magazine. She holds a bachelor's degree in physics from Tufts University and has studied physics at the University of California, Berkeley. Along with the staff of Quanta, Wolchover won the 2022 Pulitzer Prize for explanatory writing for her work on the building of the James Webb Space Telescope. Her work has also appeared in the The Best American Science and Nature Writing and The Best Writing on Mathematics, Nature, The New Yorker and Popular Science. She was the 2016 winner of the  Evert Clark/Seth Payne Award, an annual prize for young science journalists, as well as the winner of the 2017 Science Communication Award for the American Institute of Physics.