The slow wave sleep predominating in first one third of night sleep is feature of which phase of sleep?
**Core Concept**
The slow wave sleep (SWS) is a stage of non-rapid eye movement (NREM) sleep characterized by low-frequency brain waves, typically seen during the early stages of sleep. This stage is essential for physical recovery and memory consolidation.
**Why the Correct Answer is Right**
The slow wave sleep predominating in the first one-third of night sleep is a feature of stage 3 NREM sleep, also known as deep sleep. During this stage, the brain waves slow down to delta waves (0.5-4 Hz), and the body becomes less responsive to external stimuli. This stage is crucial for the release of hormones that regulate growth and development, such as growth hormone and prolactin.
**Why Each Wrong Option is Incorrect**
**Option A:** Stage 1 NREM sleep is characterized by a transition from wakefulness to sleep, with a mix of alpha, theta, and delta waves. It is not associated with slow wave sleep.
**Option B:** REM sleep is characterized by rapid eye movements, low muscle tone, and high brain activity, which is opposite to the characteristics of slow wave sleep.
**Option C:** Stage 2 NREM sleep is a lighter stage of sleep, characterized by a mix of slow waves and spindles, but not as deep as stage 3.
**Clinical Pearl / High-Yield Fact**
It is essential to note that sleep stages can be disrupted in various sleep disorders, such as insomnia, sleep apnea, and narcolepsy, which can lead to impaired memory consolidation and physical recovery.
**Correct Answer:** A. Stage 3 NREM sleep.