This post is by associate Triage Practitioner, and guest blogger, Matthew Savage
Whilst we are all told from a very early age that sleep is important, many people are not fully clear on what the actual reasons really are. Proposed functions of sleep include brain detoxification, brain thermoregulation, tissue restoration and energy conservation or “recharging” (Maquet, 2007) but a strong link also exists between sleep and memory consolidation. With over a century of research suggesting that sleep is important for memory consolidation and stabilization, it is a surprise that it still remains unclear whether or not people can learn in their sleep. What we do know is that sufficient levels of sleep ensure what we have learnt during the day can be arranged and stored by the brain where necessary (Rasch and Born, 2013) and some research even suggests that we can learn novel pieces of knowledge that we have never been learnt before during sleep.
Sleep Defined
As already noted, sleep is vital to our functioning, as a lack of it can lead to serious emotional, physical and cognitive issues, including depression, reduced immune system function, lowered libido and physical symptoms such as diabetes, high blood pressure, heart attack, heart failure and stroke. Sleep can be defined as a natural, reversable state of reduced responsiveness, meaning that we are not as responsive to external stimuli due to loss of consciousness. If we are sleep deprived, this can lead to subsequent prolonged sleep to recover (Rasch and Born, 2013) and taking a nap after learning new pieces of information can help to protect these memories, stopping them from decaying. Neuroscientists believe this consolidation occurs both whilst awake and whilst sleeping. When asleep, our bodies work through four stages of sleep with two major types of sleep defined as Slow-wave sleep (SWS) and Rapid-eye moment sleep (REM). Each stage is experienced in an alternative, cyclic manner and are defined as follows:
1) Slow-wave sleep (SWS) is a period of low frequency, high amplitude waves with slowed oscillation across the cortex, with bursts of activity called spindles occurring. These bursts of neurons are very important for memory consolidation as the neurons re-fire in the same way they did when you first formed a memory trace, and this strengthens the connections between neurons and the memory itself (Sukel, 2019). Different parts of the brain are active during this process compared to REM sleep, with the thalamus and hippocampus relatively active as the day’s experiences are stabilized and moved from the hippocampus to regions across the brain (Gholipour, 2019).
2) Rapid-eye moment sleep (REM) – This is the phase of sleep where most dreaming occurs and a person’s brain activity and other physiological responses such as heart rate and blood pressure increase. There is also some muscular paralyses, which is believed to be a protective factor for the body due to the higher level of brain activity in this stage. High frequency brain waves take place during REM and new learnings and motor skills from the day are processed, committing some to memory and deleting others (Summer, 2022).
Both stages are vital in memory consolidation which is the process whereby a memory becomes resistant to decay or further interference from other factors which may causes us to forget a memory (Walker and Stickgold, 2004). But are they associated with new learning?
Learning New Information Whilst Asleep
As far back as 1914, studies have examined whether or not we can learn new material during sleep, a process called hypnopaedia. It was established early on that learning new material just before sleep resulted in better recall compared to learning completed earlier in the day (Gholipour, 2019). Later studies supported these results also. For example, one study challenged participants to remember image and word pairings whilst awake, with associated sounds played for some words. Once the participants were asleep, associated sounds were played overnight and it was found that participants could recall the pairings that had been cued with a sound better than those which had not. This indicated that some learning should take place during the day but also that associations could be made whilst asleep (Sukel, 2019).
However, whilst it can be said that memory reactivation does take place during sleep and neurons fire in the same sequence as when a memory was created, it still remains unclear if brand new memories can be formed or new information learnt whilst asleep. Research now suggests that a basic form of learning, known as conditioning, can take place during sleep, similar to the famous experiment of Pavlov who conditioned dogs to salivate to a bell when food was present and noted the dogs continued to salivate when the bell was rung without food due to the conditioned association. A number of studies have seen humans behave in a similar way after being exposed to smells and sound pairings whilst asleep (Israeli, 2012) and another found people smoked less after smelling cigarettes paired with rotten odours overnight (Arzi, 2014). In reference to words, a number of studies have also found that, by feeding people with fake words and meanings whilst asleep, the participants could often put that fake word into a category, such as “big” or “small” or select it correctly from a multiple choice list of meanings (Zust et al, 2019).
So does this mean I can learn a new language in my sleep?
Despite strong evidence for these associations, the short answer to the above question is that it is unlikely you can learn complex information in your sleep. Most of the above studies have shown that implicit, or unconscious information fed to participants whilst they sleep, can be recalled when awake at a very basic level. However, more complex learning, such as learning new words, particularly in a different language, is not heavily supported in the literature. Something such as learning a new language is much more complex than associating sounds or smells and involves learning meaning, tone and order and this is not something which seems possible whilst asleep (Gholipour, 2019). In addition to this problem, studies have found that any new information that is fed to participants must be delivered during certain brain “up-states” of high level activity during sleep, instead of during passive “down-states”, meaning that even the stage of sleep must be optimal for simple associative learning. This has been measured by electroencephalography (EEG) and is another barrier to learning during sleep.
Conclusion
Whilst it may be possible to learn some basic information such as pairing, conditioning and associations (Mona, 2021) whilst sleeping through conditioning and implicit, unconscious memory, studies do not suggest that complex information can be learnt during sleep. It also has to be remembered that sleep is important for consolidating information we have learnt throughout the day and it is a time for the brain to encode, consolidate and store important information. It is also a time for the brain to rest and recharge so even if it is found we can learn complex information in our sleep, strong evidence already exists supporting just how important sleep is for storing knowledge, retaining important memories and allowing us to function properly to solve real world problems whilst awake – a trade-off that must be considered!
About Matt Savage
Matthew Savage is an associate triage practitioner and neurological personal trainer. He has two masters degrees, one in psychology, another in clinical neuroscience at the distinction level and is also a Level 3 Personal trainer. Matthew combines his knowledge and interest in neuroscience, cognitive and physical rehabilitation and general wellbeing to provide positive physical and mental support to his clients.
References
Gholipour, B., (2019). Can You Learn Anything While You Sleep? Livescience. Future US Inc. Doi: https://www.livescience.com/64920-how-learn-during-sleep.html
Maquet P, (2001). The Role of Sleep in Learning and Memory. Science 294, 1048. Doi: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.463.8639&rep=rep1&type=pdf
Mona, B. (2021). Can sleep Help You Learn? Here’s What Research Has to Say. Healthline. Doi: https://www.healthline.com/health/sleep/sleep-learning
Rasch, B., & Born, J. (2013). About sleep's role in memory. Physiological reviews, 93(2), 681–766. https://doi.org/10.1152/physrev.00032.2012
Sukel, K. (2019). Can You Learn in Your Sleep? Brainfacts.org. Society of Neuroscience. Doi: https://www.brainfacts.org/thinking-sensing-and-behaving/sleep/2019/can-you-learn-in-your-sleep-100419
Summer, J. (2022). What is REM Sleep and How Much Do You Need? Sleep Foundation. Doi: https://www.sleepfoundation.org/stages-of-sleep/rem-sleep
Walker, M. P., & Stickgold, R. (2004). Sleep-dependent learning and memory consolidation. Neuron, 44(1), 121–133.