Research from a team in Paris has found that new auditory memories can be formed while we sleep, as long as they are delivered during the right sleep phase. The idea we can form new memories while we slumber has been a topic of great debate among scientists in recent years and this new study demonstrates that the brain can indeed learn new information in a sleeping state.
The realm of "sleep learning" has sat precariously on the fringes of pseudoscience for decades. Subliminal sleep brain training is popular in the self-help world, but science has struggled to clearly show whether or not we do actually have a capacity to take in new information while we sleep.
The connection between sleep and memory has been the subject of much research, and the process of sleeping has been shown to play an important part in how we retain new information. This process is generally referred to as memory consolidation, where we essentially sort all the information gathered during our waking day and file it into higher cortical centers.
Exactly what information is consolidated during different sleep phases is still the subject of some debate, but the general view is that emotional memories are consolidated during REM sleep, while declarative memories such as facts and figures are consolidated during slow wave, or deep sleep.
In this new study, researchers exposed sleeping subjects to white noise that incorporated repeated patterns of tones. The goal was to study how their brains responded to those sounds at different stages of sleep under electroencephalographic analysis, and also to see if the subjects had greater recognition of these sounds upon waking, which would indicate their brains had learned the sound patterns while sleeping.
Interestingly, according to both the analysis of the EEG results and through behavioral responses after waking, all subjects seemed to display evidence of learning the sound patterns if they were heard in REM sleep phases. Learning characteristics were also displayed when subjects were in the N2 sleep phase, which occurs right before entering the slow-wave (N3) deep sleep phase.
Conversely, the opposite effect was seen in when the sounds were played to subjects across the deep sleep (N3) phase. The study found that if EEG results displayed the sound pattern as being learned through REM or N2 phases, it was effectively erased or unlearned, if subsequently played through the N3 phase.
This fascinating result further adds weight to reconciling the two seemingly contradictory theories on sleep's function in memory. The inability for subjects to imprint new memories during N3 deep sleep indicates this is most likely when the brain is effectively discarding unnecessary information. Whereas the more active N2 and REM phases indicate times when the sleeping brain can still accept information. Hence, sleep can act as both memory consolidation and "memory dump" depending on the phase.
Ultimately, this new study makes it clear that our brains are certainly able to remember auditory signals heard while asleep as long at the sounds are delivered during the correct phase. Further investigation needs to be done to see if this phenomenon translates into more complex auditory learning, such as words, but the big takeaway here is that you better time those sleep learning tapes to the right sleep phase otherwise you may be sending all that knowledge straight to the brain dump.
The research was published in the journal Nature Communications.
Source: Depasser les Frontieres