“First of all, dreaming connects.” — Ernest Hartmann, 1996
REM sleep, or dreaming sleep, is known to be an important stage of sleep for learning. One aspect of REM sleep seems to be its capacity to enable us to form new connections by integrating new experiences into our elaborate and immense network of personal experience. Several studies have looked at how associative processing in REM sleep might lead to insight or creativity.
For instance, when awakening from REM sleep, subjects are better at finding solutions to anagrams, a task that requires creative associative processing in order to rearrange a jumble of letters to produce a new word (Walker et al., 2002). In another experiment (Cai et al., 2009), subjects who took a nap that contained REM sleep performed better on a remote associate’s task, in which subjects were required to find a link between three seemingly unrelated words (i.e., Falling, Actor, Dust). Following REM sleep, but not NREM sleep or an equivalent period awake, subjects were better able to find the solution (Answer: Star).
However, REM sleep may be selective in the types of memories it chooses to integrate and associate. For instance, sleep preferentially consolidates memories that are more important for the future, such as emotional experiences. As an example, if subjects study both emotional and neutral stimuli prior to sleep, they will have better memory for the emotional stimuli after sleep.
With this in mind, a recent study attempted to assess the associative power of REM sleep on emotional vs. neutral stimuli (Carr and Nielsen, 2015). The study used a Word Associations Task, in which subjects were given a single word stimulus, either emotional (Lonely), or neutral (Canoe), and were asked to respond with three meaningful word associations. The responses provided were compared with normative data for typical word associations. For example, the three most common word associations given for the word “Lonely” are sad, alone, and depressed. A response of deserted or desolate would be considered uncommon, and thus indicative of broader associative processing.
The subjects in the study were split into three groups. The first group took a nap but was awakened from NREM sleep (after about 60 minutes), the second group was awakened from REM sleep (after about 70 minutes), and the third group stayed awake.
As expected, subjects gave less common responses following REM sleep, suggesting that REM sleep activated broader and more unusual associations between word stimuli. However, this effect was found only for emotional, and not neutral words. Further, subjects who stayed awake or had only NREM sleep consistently responded with typical word associations to both emotional and neutral stimuli.
These findings both agree with prior research and expand results to point to the preferential associative consolidation of emotional as opposed to non-emotional memory. Of note, post-hoc analyses in the study showed that the associative effect was especially strong for positive emotion words, suggesting that positive emotional experiences may particularly enhance the spreading and forming of new connections during REM sleep.
What is the function of dreaming in this process? Well, REM dreams are typically found to be immersive, vivid, emotional, and bizarre, attributes which seem to reflect the associative and emotional memory processing occurring in REM sleep.
Some researchers suggest that dreaming applies creative problem solving skills to current emotional and stressful situations. To elaborate, the open associative nature of REM sleep may provide access to a multitude of thoughts, ideas, and emotions. In this way, confronting recent stress in dreams may recruit emotional problem-solving skills unavailable while awake, providing creative solutions to current concerns.
Further, positive dream experiences may promote broad and connective associations. That the subjects in the study showed broad associations especially for positive stimuli supports this concept, which is corroborated by waking findings that positive emotion increases creativity, open-mindedness, and curiosity. On the contrary, negative dream experiences may restrict associative spread. Because of this, approaching problems with a positive mindset while awake could enhance their processing during sleep.
Here, then, are some things to consider before you go to sleep:
In sum, REM sleep integrates recent emotional memories by forming broad associations to past experience. Try some of the suggestions above to steer the connections your mind makes during sleep.
Cai, D. J., Mednick, S. A., Harrison, E. M., Kanady, J. C., & Mednick, S. C. (2009). REM, not incubation, improves creativity by priming associative networks. Proceedings of the National Academy of Sciences, 106(25), 10130-10134.
Carr, M., & Nielsen, T. (2015). Morning Rapid Eye Movement Sleep Naps Facilitate Broad Access to Emotional Semantic Networks. Sleep.
Hartmann, E. (1996). Outline for a theory on the nature and functions of dreaming. Dreaming, 6(2), 147.
Walker, M. P., Liston, C., Hobson, J. A., & Stickgold, R. (2002). Cognitive flexibility across the sleep–wake cycle: REM-sleep enhancement of anagram problem solving. Cognitive Brain Research, 14(3), 317-324.