Your Dreams Are More Complex Depending on What Stage of Sleep You're In, Study Finds

 The quality and complexity of dreams appear to vary with our stages of sleep, per a replacement analysis.

Before the twenty-first century, we accustomed think dreams only occurred during rapid eye movement (REM) sleep, but more modern research shows people sometimes recall dreams even once they are woken from non-REM stages of sleep. 

Whether these two kinds of dreaming are inherently different are a few things neuroscientists are still trying to work out.  

When patients are woken during slumber, research shows they'll usually recall elaborate, vivid, and emotional story-like dreams. In contrast, those woken during non-REM stages remember their dreams less, and also the dreams themselves tend to be more thought-like.

These are important findings, but they're also supported by subjective reports. REM dreams are often described in additional words, for example, but when the length of the outline is controlled for, differences in elaboration disappear or are highly diminished.

Researchers in Brazil have now developed a high-speed analyzing tool that may take these qualitative reports and display them in a very more objective graph form, taking under consideration biases for both length and language.

"We know REM dreams are longer and more like movies," says neuroscientist Sidarta Ribeiro from the University of Sao Paulo in Brazil. 

"Automating the method of study, as we did within the study, made possible the first-ever quantitative measurement of this structural difference."

Compared to traditional methods, which depend on parsing out the meaning of words, this non-semantic graph analysis was able to instead target the general tone of what was said.

Focusing on 133 previously collected dream reports from 20 participants, who were woken at different stages of dreaming, researchers graphed out the words, replacing them with nodes on a graph.

Analyzing their structural organization, the new tool found REM dream reports were way more complex and filled with connected information compared to dreams during non-REM sleep.

And this was true no matter the report's length.

"This is that the first study to use graph theory to point out that REM dream reports have more structural connectedness than non-REM dream reports," says neuroscientist Joshua Martin from Humboldt University in Berlin.

"Not to depreciate the relevance of traditional methods, but these results are important because they show that computational methods may be applied to studies of dreaming."

While non-REM sleep is suspected of getting some restorative function, we're still not really sure why sleep exists. If dreaming during this stage is really of unique quality, as this new research suggests, then REM and non-REM dreaming may well be driven by distinct underlying mechanisms that might play differing roles in our biology. 

Compared to REM dreams, dreams from the N2 stage – a deep, non-REM, slow-wave sleep – were shorter, less frequently recalled, less intense, and more thought-like. 

Of course, sleep studies include many limitations beyond mere subjectivity. Being woken up continuously throughout the night could itself be impacting the standard of sleep among volunteers.

Recall of dreams may additionally be warped by sleep inertia – that weird stage between waking and sleeping – although dreams' narrative complexity appears to remain identical even once participants have woken up properly.

While complex dream narratives can still occur in non-REM sleep, the authors suspect the very physiology of REM sleep, which shows great cortical activity and muscle atonia, could be a better time for interactive narratives to unfold uninterrupted.

"In this sense, dream experiences that are coherent, immersive, and story-like could also be more easily organized into a report with larger connectedness, while dream experiences that are fragmented and isolated are relatively harder to prepare mentally and thus are structurally less connected," the authors explain. 

Not only do the results of the study complement existing literature on dream reports and sleep, but they also support recent and more objective measurements of dream bank databases. 

A study published in 2020, for example, used an algorithm to sift through 24,000 dreams and located various "statistical markers" that support the hypothesis that our dreams are a continuation of lifestyle.

One algorithm isn't enough to place this mystery to bed, but mathematical tools like this one may be useful when it involves assessing our sleep and our dreams with as little bias and with as many considered factors as possible.

The current study was conducted at a way smaller scale, but it offers a number of the primary really objective measurements on dreams that we have got.