A neuroscience researcher documents that REM sleep is generated by activation of pontine cholinergic neurons (REM-on cells). Which finding is characteristic of REM sleep physiology?

• A Increased muscle tone with vivid dreaming
• B Decreased cerebral blood flow due to cholinergic vasoconstriction
• C High-amplitude slow waves with thermoregulatory conservation
• D Muscle atonia mediated by glycinergic inhibition of spinal motor neurons ✓

Explanation

REM sleep is characterized by rapid eye movements, vivid dreaming, a desynchronized (low-amplitude mixed frequency) EEG similar to wakefulness, and paradoxical muscle atonia. The atonia results from active glycinergic (and GABAergic) inhibition of spinal anterior horn motor neurons via the sublateral dorsal nucleus pathways, preventing the acting out of dreams. Cerebral blood flow actually increases in REM. Thermoregulation is impaired (poikilothermy) during REM sleep.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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