REM sleep physiology — MRCPsych Paper A MCQ

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ModerateNeurophysiology and neurochemistryREM sleep physiologyMRCPsych Paper A

A 29-year-old woman undergoes polysomnography. When awakened during one recorded epoch, she reports vivid dreaming. The EEG shows low-amplitude mixed-frequency activity, while the chin EMG shows marked muscle atonia. Which sleep stage is most likely?

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Correct answer: A — REM sleep

The correct answer is A, REM sleep. REM sleep combines cortical activation—producing a low-amplitude, mixed-frequency EEG resembling wakefulness—with profound postural muscle atonia and frequent vivid dreaming. N1 is light NREM sleep, usually characterised predominantly by theta activity rather than the full REM pattern. N2 is identified by sleep spindles and K-complexes. N3 is slow-wave sleep and shows high-amplitude delta activity. Quiet wakefulness may also produce relatively low-amplitude EEG activity, but normal skeletal muscle tone is retained; marked chin-EMG atonia therefore strongly favours REM sleep. The concurrence of wake-like EEG activity and motor inhibition accounts for the description of REM sleep as paradoxical sleep.

Reference: Brown RE, Basheer R, McKenna JT, Strecker RE, McCarley RW. Control of sleep and wakefulness. Physiological Reviews. 2012;92(3):1087–1187. See Figures 1 and 10 and the REM sleep section. https://pubmed.ncbi.nlm.nih.gov/22811426/