For a long time, it was generally accepted that dreams only occur during REM sleep. However, scientists then found out that we have different kinds of dreams throughout the night, based on changes in the activity of our brain, eye movement, and muscle tone. These changes reflect different stages of sleep: REM (or Rapid Eye Movement) and non-REM, or “slow-wave” sleep.
However, how do these dreams differ from each other? And why is REM sleep much shorter than slow sleep? Scientists led by Joshua M. Martin from the Federal University of Rio Grande do Norte, Brazil, tried to answer these questions. Previous studies have shown that we are more likely to remember REM dreams – they account for 82% of all remembered dreams upon awaking. That is why scientists used to believe that dreams only occur in the rapid phase. After all, we very rarely remember any other kind of dream.
In addition, the memories of REM dreams are more detailed and longer than those of non-REM phase. This is evidenced by reports describing dreams. Unlike REM dreams, other dreams are mostly riddled with “blanks spots”: for example, we might remember that we dreamed of our grandmother, but we do not remember the plot of the dream. Reports of dreams in the fast and slow phases also differ in content: REM dreams are described as more vivid, bizarre, and emotional, in which we are completely immersed in a parallel universe created by our imaginations.
In their experiment, the scientists analyzed data from 133 dream reports by analyzing words received from twenty participants in a sleep laboratory. Participants were awakened during the REM and non-REM sleep phases recorded by polysomnography. The results of the experiment confirmed previous findings and found a larger structural connectedness in REM sleep reports. This means that the descriptions of these dreams are more similar to stories, in which we use more unique words, emphasizing their complex structure.
REM dreams were recalled by 90% of the participants, who described them as continuous narratives, while slow dreams were made up of unrelated visual images (42.5%) or conceptual, non-visual experiences (13.79%). During REM sleep, our brain is more active, while the body is completely relaxed due to muscle atony, which allows us to fully immerse ourselves in an interactive dream environment or see lucid dreams. However, slow sleep is necessary for us to rest and restore the body, which is why these phases alternate. Many advanced practitioners are able to control the transitions between these phases by prolonging their REM sleep to deepen lucid dreaming.
The article was published in July 2020 in the journal Plos One.
