The Biology of REM Sleep

Abstract

• Recent advances in understanding REM sleep due to neuroscience tools.
• REM sleep impacts sensorimotor function.
• Review covers:
  • Discovery of REM sleep
  • REM sleep diversity across species
  • Functions of REM sleep
  • Neural circuits controlling REM sleep
  • Disorders linked to REM sleep dysfunction.

Introduction

• REM sleep discovery credited to Eugene Aserinsky, Nathaniel Kleitman, William Dement, and Michel Jouvet.
• Characterized by:
  • Rapid eye movements
  • Specific brain-wave patterns
  • Muscle atonia
  • Cortical activity similar to wakefulness.
• REM sleep alternates with non-REM sleep.
• Important for memory consolidation.

REM Sleep Across Species

• Found in terrestrial mammals, birds, reptiles, and some aquatic invertebrates.
• Variations in REM sleep duration and cycle across species.
• REM sleep critical for brain development in newborn mammals.
• Expression varies due to environmental and ecological pressures.

REM Sleep Function

• REM sleep’s role in biology and neuropsychiatry is still unclear.
• Potential functions:
  • Brain development
  • Sensorimotor learning
  • Memory consolidation and synapse regulation.
• Studies show REM sleep deprivation impairs memory.
• REM sleep may aid in creativity and readiness for wakefulness.

Brain Circuitry Controlling REM Sleep

• REM sleep involves circuits in the brainstem, especially the sublaterodorsal nucleus (SLD).
• SLD neurons produce motor atonia by activating inhibitory interneurons.
• Involves REM-on and REM-off neurons creating a flip-flop switch.
• Orexin and melanin-concentrating hormone (MCH) neurons influence REM sleep.

Pathobiology of REM Sleep

• Disorders include REM sleep behavior disorder (RBD) and narcolepsy.

REM Sleep Behavior Disorder (RBD)

• Loss of normal REM sleep paralysis, leading to motor behaviors during sleep.
• Linked to neurodegenerative diseases like Parkinson's.
• May result from synucleinopathy-induced degeneration of REM circuits.

Narcolepsy/Cataplexy

• Linked to loss of hypothalamic orexin cells.
• Characterized by excessive sleepiness, disrupted REM sleep, and cataplexy.
• Cataplexy involves intrusion of REM sleep paralysis into wakefulness.
• Emotional triggers may link cataplexy with REM sleep circuits.

Conclusions and Future Directions

• Significant progress in understanding REM sleep's mechanisms and functions.
• Remaining questions:
  • Universal presence of REM sleep in animals
  • REM sleep's role in learning and memory
  • Complete identification of REM sleep circuits.
• Importance of studying REM sleep in relation to human diseases, particularly neurodegenerative disorders.