Not a feature of paradoxical sleep is :
**Core Concept**
Paradoxical sleep, also known as REM (rapid eye movement) sleep, is a stage of sleep characterized by rapid eye movements, low muscle tone, and high brain activity, similar to being awake. This stage is crucial for memory consolidation, learning, and emotional regulation.
**Why the Correct Answer is Right**
During paradoxical sleep, the body is paralyzed through a process called atonia, which prevents acting out dreams. This is mediated by the inhibition of motor neurons in the spinal cord by the brainstem, specifically the locus coeruleus and the raphe nuclei. This inhibition is essential to prevent physical harm during the intense, often vivid dreams experienced during REM sleep.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because reduced body temperature is indeed a feature of paradoxical sleep, as the body's thermoregulatory mechanisms are less active during this stage.
**Option B:** Incorrect because increased heart rate is a characteristic of paradoxical sleep, as the body's autonomic nervous system is active, preparing the individual for potential threats.
**Option C:** Incorrect because increased brain activity is a hallmark of paradoxical sleep, as the brain undergoes intense neural activity, similar to being awake.
**Clinical Pearl / High-Yield Fact**
Remember that paradoxical sleep is essential for memory consolidation and learning, and its disruption can lead to impaired cognitive function and mood disorders.
**Correct Answer: C. Increased body temperature.**