Like every overachiever in high school, I had always wondered if there was some way to use sleep for something productive. You spend a third of your life asleep, is there some way to get an edge from it? The idea of learning in your sleep via dreams is ancient, but how much of the real world actually bleeds over?
Pretty much everyone has a memory of “learning” something in their sleep and recalling it later. Anecdote doesn’t really prove anything though, and science has struggled to get close. Jung’s theories on the unconscious included the idea that dreams were the integration of conscious and unconscious ideas. Dreams communicate what the unconscious interprets, but also what it observes. While I love Jung’s theories, a lot of them are typically considered metaphysics or philosophy rather than hard science.
Sleep is important, but science has barely scratched the surface of what exactly sleep does. It’s important, it touches on learning, it cleans the brain, but what exactly is it? Science has been struggling with this question for ages.
What Science Shows
An experiment (II. A.) done by Rosa Heine in 1914 provided some of the first scientific evidence linking sleeping and learning. Soon after came the Psycho-Phone which supposedly inspired you as you sleep with a recording of various, inspirational key phrases. The concept ties in with the Jungian idea that the subconscious communicates with the conscious mind via dreams or sleep.
Older claims were pretty much all debunked, but more recent science has shown some evidence of learning in sleep. Participants were tested on hearing a noise when sleeping on whether they could more readily identify it during a conscious learning session. The issue with this study is that the benefits depend on the phase of sleep (REM [Rapid Eye Movement] or NREM [Non Rapid Eye Movement]), and to top it off, stimuli during deep NREM can harm learning upon awakening.
This isn’t the only experiment of its type. We get a negative association with arbitrary learning in the previous experiment, but what happens with something more focused? Different experiments tested different aspects of this concept.
Novel information can be learned in sleep. Linguistic information can be learned or reinforced in NREM sleep. Input during sleep can reinforce skills.
Novel Information in Sleep
New information can be acquired during REM sleep. The experiment for this study used simple nonverbal cues to create associations. Smells combined with tones led to a novel association.
A similar study was done making associations between cigarettes and unpleasant odors. Subjects which were exposed to the unpleasant odors in conjunction with cigarette odor tended to smoke less. This study also had a difference in the stages of sleep with the second stage of (NREM) sleep having the biggest effect (34.4 ± 30.1%) while REM sleep had a smaller effect (11.9 ± 19.2%).
This at least shows learning in our sleep is possible, but the specifics get a bit complicated. Newer research just adds to the complexity. Will that “learn a language in your sleep” app do something or is it all pseudoscience? Have we jumped to conclusions or gotten ahead of the game?
Linguistic Learning in NREM Sleep
A study done with German participants learning Dutch vocabulary found evidence that listening to linguistic input during NREM sleep led to better than average linguistic advancement. They weren’t putting on a podcast and waking up fluent in Dutch, but they were getting something out of it. Further re-exposure to the input led to an even greater understanding, like that acquired via repetition or study.
Another experiment showed evidence of implicit vocabulary learning during NREM sleep as well. Slow-wave peaks correlated to better retention and encoding. This experiment used a made up set of words which ruled out any kind of subconscious knowledge about the terms.
Research hasn’t really touched on a full-on language learning approach, but we know at least some level of linguistic input is possible. We barely understand sleep, let alone the number of variables which would go into just constructing such a study. The conclusion we get is that at least we get some positive linguistic learning during NREM sleep (in a controlled setting).
Input for Skills
A further study delves into whether sleep can be used to reinforce skills rather than target novel learning. Participants learned a sequence in conjunction with a melody like any number of rhythm games or musical games (think Guitar Hero or similar). Participants which heard the melody while napping during the slow-wave phase (deep NREM interspersed with REM) did better than those who didn’t hear the melody while napping.
Sleep doesn’t just improve learning, it improves reinforcement as well. There are all sorts of reasons to learn a new language, and the learning process requires learning and reinforcement. Research hasn’t really gotten that much further into the crossover between sleep and language learning (as of writing at least).
Further Research
Future research would need to address what the connection is to really answer our question. While we have what appears to be many relevant pieces which should give us some degree of progress with learning a language or similar, we only have potential pieces to the puzzle. Can these pieces even fit together? Just how much learning actually goes on during sleep and is it worth it?
At least one experiment has suggested a negative correlation with learning attempts during a specific phase of sleep. Others have focused on only specific phases or seen neutral or better. Where is the line, or is it variable depending on content?
It will take a huge amount of work to really nail down whether complex learning occurs during sleep. There aren’t really any compelling studies which suggest complex learning at present though. Bits and pieces might work, but that doesn’t mean they complement one another.
Learning Materials
Each of our experiments has a specific methodology that it uses, and we don’t have a known limit to complexity. Will any learning materials provide some value, or is their a complexity limit? Most “subliminal learning” courses expect some passive uptake in information. YouTube, or your platform of choice is littered with “learn [thing] while you sleep” courses, lessons, etc.
Even if the method itself works, is the content using the right methodology? There really isn’t a right answer until an experiment provides it unfortunately. We have a loose correlation that our brain can learn certain types of structured information in sleep, and that it can also learn unstructured information sometimes, but nothing really showing the limits (if any) of sleep learning.
Conclusion
Sleep learning feels a bit like supplements at the moment. You have an answer which says that certain things correlate in certain situations, and the natural logical jump is to put them together because they fit. While the pieces fit, it doesn’t mean it’s more than coincidence.
We can learn certain arbitrary pieces of information under certain conditions, we can be primed for linguistic learning under other certain conditions, and skills can be reinforced, but nothing says that all of these can be chained together in a way which beats conscious studying. Sleep might provide value for learning, but is the juice worth the squeeze? The answer is unfortunately an unenthused “maybe” at best.
A lot more work needs to be done to actually determine whether this process is a net gain or loss. We can see specific cons in specific scenarios. Modern psychology points to sleep as a reinforcement of memories and research shows that learning during sleep can clash with learning on awakening.
I wouldn’t put much stock in it personally, but I also wouldn’t turn off a quiet lecture that helped lull me to sleep. I’ve had dreams about things I’ve heard sleeping and I’ve had dreams about complete nonsense despite hearing things. There’s potential in general, but a lot more (or less) potential on an individual basis. Science can’t tell you right now, but you can always take a leap of faith if you’re willing. Does it work for you or does it not? That’s the best you get right now.
Image by alessandra barbieri from Pixabay