REM behaviour disorder results from which underlying problem that occurs during rapid eye movement sleep?

Introduction / Context:
This question examines your knowledge of sleep physiology, specifically rapid eye movement sleep and a condition called REM behaviour disorder. Understanding what normally happens to skeletal muscle tone during REM sleep and what goes wrong in this disorder is important in neurology and psychiatry. The correct option describes the key pathophysiological change that leads to dramatic acting out of dreams.

Given Data / Assumptions:
- Rapid eye movement sleep is a stage of sleep associated with vivid dreaming.- In healthy individuals, there is profound loss of skeletal muscle tone, often called atonia, during REM sleep.- REM behaviour disorder is a clinical condition in which people physically act out their dreams.- The question asks for the underlying problem that produces this disorder.

Concept / Approach:
The key concept is that REM behaviour disorder results from failure of the brainstem mechanisms that normally silence most skeletal muscle activity during REM sleep. This atonia protects the sleeper from enacting the dream content. In REM behaviour disorder, this protective paralysis is incomplete or absent, so the dreamer may kick, punch, shout or perform complex behaviours. The strategy is to identify which option refers to loss of muscle paralysis, and to distinguish this from other sleep problems such as obstructive sleep apnoea, insomnia or simple poor dream recall.

Step-by-Step Solution:
Step 1: Recall that normal REM sleep shows rapid eye movements, vivid dreams and almost complete paralysis of skeletal muscles.Step 2: In REM behaviour disorder, patients act out their dreams, indicating that muscle paralysis is not functioning properly.Step 3: Consider each option and look for a description of this failure of muscle atonia.Step 4: Option A explicitly states loss of the normal muscle paralysis during REM sleep, which matches the known mechanism of REM behaviour disorder.Step 5: Confirm that the remaining options describe other sleep issues, such as abnormal hormone secretion or airway obstruction, which do not match the disorder in question.

Verification / Alternative check:
A quick textbook style description of REM behaviour disorder highlights dream enactment behaviours due to failure of REM related muscle atonia.Polysomnography studies show increased muscle activity during REM episodes in affected individuals.These facts directly support option A and rule out explanations based purely on melatonin levels, airway obstruction or absence of eye movements.

Why Other Options Are Wrong:
Option B is wrong because people with REM behaviour disorder still experience rapid eye movements; the problem is not absence of REM but loss of muscle paralysis.Option C is wrong because failing to remember dreams is common in many people and is not a violent dream enactment disorder.Option D is wrong because melatonin levels are associated with sleep timing rather than specific acting out of dreams.Option E is wrong because upper airway obstruction and loud snoring describe obstructive sleep apnoea, which involves breathing pauses rather than complex motor behaviours tied to dream content.

Common Pitfalls:
A frequent misconception is to equate any unusual night time movement with sleepwalking, which occurs mainly in non rapid eye movement sleep, not in REM sleep.Another pitfall is to confuse REM behaviour disorder with nightmares, which involve distressing dreams but not necessarily vigorous physical enactment.Some learners also assume that hormone imbalances such as altered melatonin are responsible for all sleep disorders, which is not the case here.

Final Answer:
REM behaviour disorder results from loss of the normal muscle paralysis that should occur during rapid eye movement sleep.