Emotions are some of our strongest memory enhancers. When we consider which episodic events from the past are most memorable, they are often tied to specific and strong emotions. Whether it’s the memory of joyous birthdays, or the stress of losing your parents in a store as a child, or even grief associated with the death of your first pet – these memorable past events are laced with palpable emotion. Science suggests that we tend to remember negative experiences slightly more than positive experiences. From an evolutionary perspective, this makes sense. Emotions like fear, pain, or sadness, when tied to a memory, help prevent us from repeating behaviors that brought about those emotions in the first place. If you were painfully bitten by a snake while hiking, it would help to remember this memory long after so that when hiking or walking outside in the future you may use greater caution. While from a survival standpoint remembering emotional events is beneficial, this process has particular implications. Notably, traumatic experiences are more likely to be consolidated and stored in our long term memory.
REM sleep is a sleep stage in which key emotion and memory structures in the brain including the amygdala, emotion-regions of the cortex, and the hippocampus are active (Walker 208). For this reason, REM is believed to aid the consolidation of emotionally toned memories (Walker 208). The transfer of traumatic memories and their associated emotions to our long term memory during REM-sleep is of particular importance to researchers and trauma exposed individuals alike. A traumatic event can greatly impact a person’s quality of life, causing fear, anxiety, and depression to permeate their everyday experiences. It can also lead to Post-Traumatic Stress Disorder or PTSD, which is characterized by flashbacks, nightmares, or severe anxiety after a traumatic event (Mayo Clinic). Interested in reducing emotional suffering and PTSD-onset after a trauma, researchers have hypothesized about sleep interventions following a trauma.
Because REM sleep aids in memory consolidation, it may actually strengthen emotionally-rich traumatic memories and contribute to the development of psychopathologies like PTSD. As an intervention, it has been theorized that sleep deprivation following a trauma may reduce consolidation and thereby protect an individual from emotional suffering (Repantis et al 2020). Unfortunately, two-pronged pilot study in Germany aiming to first delineate the relationship between sleep and traumatic memories, and follow up by examining sleep deprivation failed due to lack of consenting participants (Repantis et al 2020). Individuals asked to enroll in the study declined, with the majority feeling it would be too burdensome to use a polysomnography at home following a trauma (Repantis et al 2020). Notably, the detrimental effects of sleep deprivation, from impaired emotional regulation, drowsiness, and even weakening of the immune system, are alarming (Walker). Do the potential benefits of reduced consolidation really outweigh the risks of sleep deprivation? This is still up for debate in the scientific community, but perhaps the answer is no. Do other therapies have less side-effects and are more effective? Maybe, hopefully, yes!
In this review paper, researchers set forth a secondary, yet contradictory, hypothesis for sleep intervention after trauma. While sleep deprivation, and specifically REM deprivation, may prevent consolidation of a memory, sleep itself may have significant therapeutic benefits (Repantis et al 2020). May we recall that in the book, Why We Sleep, Matthew Walker, a well known sleep researcher, called REM-sleep a “soothing balm” that “takes the painful sting out of difficult, even traumatic, emotional episodes” (Walker 207). The therapeutic nature of sleep itself, especially REM sleep’s ability to consolidate a memory and tenuate the emotional tinge of that memory in healthy individuals is promising. In the context of the snake bite mentioned earlier, it would be like remembering the painful bite and events surrounding the trauma, but not having to re-experience the visceral emotional conditions of the trauma when recalling the memory.
While REM may strengthen a memory, promising studies suggest that REM sleep may also successfully reduce the emotional tone of that particular memory. A newly published paper looked to rats to examine the effect of sleep enhancement on fear-associated memory processing after a trauma. Optogenetically engineered rats were exposed to lengthy prolonged stressors to induce behavioral changes that resemble PTSD in humans (Davis and Vanderheyden 2020). Subsequently, optogenetic activation of hypothalamic melanin-concentrating cells occurred for one out of every five minutes for seven days following the single prolonged stress condition in the experimental group; the control group received no stimulation (Davis and Vanderheyden 2020). The experiment found that in comparison to the control, optogenetically stimulated rats experienced significant increases in REM sleep duration and significantly improved fear-associated memory processing (Davis and Vanderheyden 2020). Although the results are limited by not examining long-term effects on rats, these findings suggest that post-trauma REM sleep is a valid therapeutic.
Davis and Vanderheyden’s findings will likely lead to enhanced post-trauma therapeutic seeking sleep research. I am eager to see what new information will be found in coming years because many questions still remain unanswered. Namely, how long do the therapeutic effects of post-trauma REM sleep last? And, how much extra REM sleep would an individual need to achieve these therapeutic effects? Would the amount needed for therapeutic benefits be realistic? Moreover, how do we achieve such enhanced REM sleep in humans, especially when there are very few drugs that are known to increase the duration of REM?
Another important consideration is whether or not this intervention would help individuals suffering from PTSD. PTSD can develop from within three months to even years after a traumatic experience (Mayo Clinic). Additionally, PTSD patients have been found to have numerous sleep disturbances from decreased sleep time and slow wave sleep, to increased waking after falling asleep, and most notably, significantly decreased REM (Zhang et al. 2019). It brings into question whether or not increasing REM-sleep in these individuals would have similar therapeutic effects to enhancing REM-sleep immediately following a traumatic event. Perhaps though there is a time constraint on the benefits of sleep. The consolidation of a traumatic memory is of particular importance. PTSD is thought to arise when the emotional tinge of a memory is not sufficiently separated from the memory itself. Because of this, REM-enhancing therapies may only benefit individuals who have yet to consolidate the traumatic memory.
Moreover, Davis and Vanderheyden’s findings highlight potential limitations of current, and widely used, therapies for PTSD sufferers. Beyond cognitive and exposure therapy techniques, PTSD patients are often given SSRIs to combat depression and anxiety that often co-occur with the mental condition (Mayo Clinic). However, these therapies are known to decrease the amount of REM, and may not actually benefit an individual’s fear-based trauma processing (Davis and Vanderheyden 2020). It will be interesting to see what impacts these findings have on the future of PTSD therapy as a whole.
Overall, it is safest to say that we don’t know if we should prescribe sleep to ameliorate the acute and chronic emotional distress caused by a traumatic event. In keeping with my scientific self, I don’t want to jump to conclusions. It is clear that future research is needed to better parse out the role of sleep in fear-associated memories following a traumatic event, and even clearer that many more questions will arise from new research.
Davis, Christopher J., and William M. Vanderheyden. “Optogenetic Sleep Enhancement Improves Fear-Associated Memory Processing Following Trauma Exposure in Rats.” Nature News, Nature Publishing Group, 22 Oct. 2020, www.nature.com/articles/s41598-020-75237-9.
“Post-Traumatic Stress Disorder (PTSD).” Mayo Clinic, Mayo Foundation for Medical Education and Research, 6 July 2018, www.mayoclinic.org/diseases-conditions/post-traumatic-stress-disorder/symptoms-causes/syc-20355967.
Repantis, Dimitris et al. “REM sleep in acutely traumatized individuals and interventions for the secondary prevention of post-traumatic stress disorder.” European journal of psychotraumatology vol. 11,1 1740492. 6 Apr. 2020, doi:10.1080/20008198.2020.1740492
Walker, Matthew P. Why We Sleep: the New Science of Sleep and Dreams. Penguin Books, 2018.
Zhang Y., Ren R., Sanford L. D., Yang L., Zhou J., Zhang J., … Tang X. (2019). Sleep in posttraumatic stress disorder: A systematic review and meta-analysis of polysomnographic findings. Sleep Medicine Reviews. doi:10.1016/j.smrv.2019.08.00