Goal of the Study?

In this review article from Current Biology Review.1 the authors’ singular goal was to update the general scientific community about recent mechanistic, functional and conceptual development in understanding REM sleep biology and pathobiology.   This review also outlines the historical origins of the discovery of REM sleep, the diversity of REM sleep expression across and within species, the potential functions of REM sleep, the neural circuits that control REM sleep, and how dysfunction of REM sleep mechanisms underlie debilitating sleep disorders such as REM sleep behaviour disorder and narcolepsy. 

Why are they doing this study?

The functional role of REM sleep in normal biology remains an open question as well as one of the more intriguing mysteries in science. Indeed, Science magazine identified how and why we dream during REM sleep as one of the most important and conspicuous knowledge gaps in science. Although REM sleep appears important for certain types of learning and memory, it remains virtually unknown how REM sleep actually facilitates plasticity and learning.  It also remains unclear if REM sleep serves the same biological function(s) across the lifespan. It is unknown why REM sleep amounts are typically higher in young and developing animals than in older ones? These age-related differences in REM sleep amounts suggest that REM sleep function may vary across an animal’s lifespan, but those potential functions remain unclear.

What was done?

An up-to-date review of the recent pathobiology of REM sleep in both humans and animals.

 

What did they find?

The amount of REM sleep can vary across and within species and their development age.  Some animals like birds and sea mammals seem to be able to expand and contract their REM sleep based on their environment and ecological pressures.  One of the more widely supported ideas is that REM sleep functions to facilitate the formation and consolidation of certain types of spatial and emotional types of memories.  Other functions ascribed to REM sleep range from facilitating cortical plasticity, restoration of aminergic cell receptor functions and improving general creativity.  REM sleep increases toward the end of the sleep period and there is some emerging evidence to suggest it may also function as a stimulus to the central nervous system to prepare for wakefulness.

Why do these findings matter?

REM sleep Behaviour Disorder (RBD) is a neurological condition characterized by loss of the biological mechanisms that cause REM sleep paralysis, resulting in excessive motor behaviours during REM sleep. Movements in RBD range from shouting and sporadic limb jerks to more complex movements such as punching or kicking. These movements in RBD are not innocuous as they can result in a physical injury of the patient and/or their bed-partner. But, the most alarming aspect of RBD is that the majority of patients develop a neurodegenerative disease within 6–15 years of initial RBD diagnosis.  RBD is currently the strongest known predictor of a class of neurodegenerative disorders known as synucleinopathies with 80-90% of patients developing Parkinson’s disease, dementia with Lewy bodies or multiple system atrophy.