It is a well-known fact that humans need a lot of sleep to function normally. We spend almost a third of a day asleep, and at the end of our lives will have spent around 25 years asleep. It is recommended to sleep for around 7 or 8 hours, but many individuals get significantly less due to stress, school, or work. Sleep is broken up into two general parts – non-REM sleep and REM sleep – that are distinguished based on the presence or lack of rapid eye movements. Non-REM sleep is broken into four stages; stages 1 and 2 are considered light sleep and stages 3 and 4 are considered deep sleep. Throughout a night of sleep, you cycle through the stages before entering brief periods of REM sleep.
REM sleep is the closest a person is to being awake and is the part of a night of sleep where you are dreaming. Sleep is still a bit of a mysterious and controversial process, as research has provided differing results about the function of sleep. In the future, research is needed to look into the mechanisms that occur during sleep in order to understand how exactly sleep works to promote learning and memory.
Previous research ties sleep closely with memory consolidation. Interruption of REM periods and deprivation of REM sleep have been shown to negatively affect one’s ability to encode an associative memory (Roe, Walsh & Bjorness, 2010). This is thought to be related to the importance of sleep in maintaining LTP within hippocampal and frontal cortex neurons and facilitating the neuronal plasticity (Romcy-Pereira & Pavlides, 2004). However, REM-sleep deprivation both impaired and enhanced LTP in different parts of the brain, providing conflicting evidence (Romcy-Pereira & Pavlides, 2004) about the relationship between sleep and memory. Interestingly, research showed that REM sleep deprivation of over two weeks had no negative effects on behavior and functioning (Purves et al., 2001). It is likely but still unclear that REM sleep is essential for normal memory processes, as it seems that REM sleep deprivation has conflicting effects.
To bring in another piece to the puzzle, the relationship between REM sleep and antidepressants is a very interesting one. Individuals diagnosed with depression often have trouble sleeping and lack of sleep is something that treatment should address. Antidepressant drugs tend to further disrupt sleep, especially REM sleep. Across treatment drug classes (e.g. MAOIs or SSRIs), REM sleep decreased and latency to enter REM sleep increased for almost all classes (Wichniak et al., 2017). This suggests that reduced REM sleep is key in treatment for depression, and individuals taking antidepressants generally do not have any apparent side effects of this reduction.
Furthermore, one of the main parts of REM sleep that distinguishes it from other sleep stages is the experience of dreams. Ranging from very realistic to wildly unrealistic, the purpose of dreaming has been speculated about for years. There are many hypotheses regarding the purpose of dreams, but the question still remains unanswered. Dreams could be a way to regulate one’s emotions – the scenarios during a dream could help us understand and make sense of how we feel. Dreams could be a place for the mind to work out any negative emotions that someone might be feeling, instead of letting them burst out at inopportune times during the day. Likewise, dreaming may be a way for the brain to process events during the day. Dreaming could also be related to memory consolidation in a way that parts of our dreams are based on what we experienced during the day, and by going over these events or salient parts of the day during a dream helps to solidify them into a memory. Commentary around dreaming has also brought up the idea that dreaming is a separate state of consciousness in which we perceive and emote but in a simulation of reality. In this state of consciousness, the brain is able to understand consequences of actions to be done in the future (Hobson & Friston, 2012). However, not everyone dreams and this does not seem to be a problem. The true purpose of dreams has not been discovered, but it does not appear that absence of dreams has any negative impact on normal functioning.
General sleep deprivation has devastating results on cognition, behavior and brain structure. Periods of sleep deprivation have tangible consequences, which contrasts with the apparent lack of consequences of REM sleep deprivation. So, do we really need REM sleep to function?
Hobson, J. A. & Friston, K. J. (2012). Waking and dreaming consciousness: Neurobiological and functional considerations. Progress in Neurobiology 98(1): 82-98.
Purves, D., Augustine, G. J., & Fitzpatrick, D., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001. The Possible Functions of REM Sleep and Dreaming. Available from: https://www.ncbi.nlm.nih.gov/books/NBK11121/.
Roe, G. R., Walsh, C. M., & Bjorness, T. E. (2010). Both duration and timing of sleep are important to memory consolidation. Sleep 33(10): 1277-1278.
Romcy-Pereira, R. & Pavlides, C. (2004). Distinct modulatory effects of sleep on the maintenance of hippocampal and medial prefrontal cortex LTP. European Journal of Neuroscience 20(12): 3453-3462.
Wichniak, A., Wierzbicka, A., Walecka, M., & Jernajczyk, W. (2017). Effects of antidepressants on sleep. Current Psychiatry Reports 19(9): 63. doi: 10.1007/s11920-017-0816-4.