Exploring the Mystery of REM Sleep

“To sleep, perchance to dream”

What role does REM sleep play in humans and animals?   And why do we dream at all?   Ever since the 1950s, researchers have known that sleep occurs in different stages and that the deepest part of sleep, which usually happens in the early hours of the morning, can be recognized by rapid, random eye movements.  

This stage of sleep is now known as REM (rapid eye movement) sleep and is linked to extremely vivid dreaming.   Among the different theories about REM sleep’s function are that it helps in forming new memories, stimulates the central nervous system, and  restores brain chemistry to a normal balance. 

Along with rapid eye movements,  REM sleep is also recognized by low muscle tone and a rapid, shallow EEG pattern.  In most adults, REM sleep can happen four or five times on average each night making up only 25% of the total time spent sleeping.   Researchers have also found evidence of REM sleep in almost all land-based mammal and bird species and even some aquatic mammals such as dolphins. 

As for how REM sleep first evolved, a recent article published in the journal Dreaming has suggested an intriguing new hypothesis.  Written by Ionnanis Tsoukalas of Sweden’s Stockholm University, the article suggests that REM sleep, and dreaming in general, evolved out of an ancient defense mechanism still seen in many species.   Of different defense mechanisms used by animals in danger, Tsoukalas’ article focuses on tonic immobility, or the faint response.  

To read more, check out my new Psychology Today blog post.


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