Recent study suggests dreams are related to a 'memory replay' function of sleep.

Many sleep researchers avoid sampling dreams in their studies, perhaps because dreams can be difficult to record, quantify, and analyze. Instead, sleep research tends to focus on more tangible measures, such as patterns of brain activation, to try to understand how sleep functions in learning and memory. One of the first breakthroughs in dream science came in 1953, when researchers Aserinsky and Kleitman linked dreams with a quantifiable characteristic of sleep, specifically the "rapid eye movements" of REM sleep. Because rapid eye movements are easily detected, we are able to better predict when dreams are occurring by looking at corresponding eye movements. In fact, it's thought that eye movements are actually a signal that the eyes are "scanning" the dreamworld, also known as the scanning hypothesis.


Michelle CarrMichelle Carr, Ph.D, is a researcher at Swansea University Sleep Laboratory. She holds a PhD in Biomedical Science from the University of Montreal, where she conducted research at the Dream and Nightmare Laboratory. Prior to that, she received dual degrees, a BS in Brain and Cognitive Science and a BA in Psychology, from the University of Rochester in 2010. Her work focuses on the role of REM sleep and dreams in emotional memory, along with comparative studies of nightmare disorder and PTSD. Other research interests include sleep paralysis, lucid dreaming, consciousness studies, and the use of dreamwork in psychology.

Editor: Saad Shaheed


A new study in Sleep Spindles & Cortical Up States (2016) just broke another barrier in dream research. The authors found that the frequency at which people recall dreams is actually related to brain activity during another phase of sleep, non-REM sleep (a period without eye movements). This exciting finding further supports the notion that dreams are not simply epiphenomena, or meaningless by-products of sleep—they are intricately related to the neurophysiology and functional patterns of sleep.

The study looked at the short bursts of brain activity that occur during non-REM sleep, called "sleep spindles." These spindles appear as a quick ripple of activity that researchers can easily spot on a polysomnogram. Spindles have become a measure of interest in many areas of sleep research because they are consistently associated with memory consolidation during sleep, along with more general measures of intelligence and cognitive abilities. It’s thought that these bursts of activity are actually responsible for transferring memory from short term to more stable long term stores in the brain; in other words, these spindles carry recent experiences into more stable memory stores while you sleep. 

Many researchers think that dreams also are related to the "replay" and consolidation of memory during sleep, and dream recall has been related to general intelligence and performance on various tasks. For instance, individuals who recall more dreams actually perform better on a mirror tracing task, where you have to trace a figure by regarding only its reflection in a mirror (Dumel et al., 2015). According to this study, having better visuospatial capacity may equip these individuals to generate and/or recall more vivid dreams during sleep.  

Another phenomenon in dream research, the "day-residue" effect, refers to the consistent finding that people tend to dream about experiences of the previous day, such as experimental stimuli that were presented in the laboratory. Many researchers believe that day-residue, like spindles, reflects a form of memory replay that functions to consolidate recent experiences during sleep. 

Nonetheless, the findings linking sleep spindles with intellectual abilities and memory consolidation are much more robust and consistent than any evidence for dreaming's role in memory. The current study thus set out to explore whether there exists a relationship between the two.

A total of 53 participants, averaging 24.2 years old, completed a sleep and dream log from home by telephone for two weeks; they called a recording system each morning to report their sleep pattern and respond to questions about their dreams. Participants reported whether they had any dreams the previous night, and whether they were bad dreams or nightmares. Participants also spent one night in the laboratory for an EEG-recorded sleep; these EEG recordings were used to calculate the number of sleep spindles that occurred during the night. Finally, analyses were conducted to assess whether there was a relationship between the frequency of dream recall during the two-week dream log and the number of sleep spindles recorded during the night in the lab.

The results showed that the density of sleep spindles was significantly correlated with the number of dreams, bad dreams, and nightmares recalled during the two-week period. Interestingly, the correlations were somewhat stronger for the bad-dream recall measure, suggesting that the relationship between spindles and dreaming might be specifically linked to some emotional memory function of sleep and dreaming.

The authors suggest that both dreams and their physiological neighbor, the sleep spindle, may reflect forms of "memory replay" that occur during sleep. While further research is warranted, the findings are a welcome development for dream researchers, who, in majority, have long maintained that dreams are related to the function of sleep.

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