**Core Concept**
Sleep is a complex physiological state characterized by distinct stages, including REM (Rapid Eye Movement) and NREM (Non-Rapid Eye Movement) sleep. REM sleep is associated with rapid eye movements, increased brain activity, and vivid dreams. The electroencephalogram (EEG) is a crucial tool for assessing brain activity during sleep, and different stages of sleep are characterized by unique EEG patterns.

**Why the Correct Answer is Right**
During REM sleep, the EEG rhythm recorded from the surface of the scalp is predominantly alpha and beta waves. Alpha waves (8-12 Hz) are typically seen in relaxed, closed eyes states, while beta waves (13-30 Hz) are associated with active, attentive states. The presence of alpha and beta waves during REM sleep reflects the increased brain activity and cortical excitability characteristic of this stage. This is in contrast to NREM sleep, where delta and theta waves are more prevalent.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect, as beta waves are indeed present during REM sleep, but alpha waves are not typically associated with this stage.
**Option B:** Incorrect, as alpha waves are not characteristic of REM sleep; they are more commonly seen in relaxed, closed eyes states.
**Option C:** Incorrect, as delta waves are typically seen in deep NREM sleep, not during REM sleep.
**Option D:** Incorrect, as theta waves are more commonly associated with drowsiness or early stages of NREM sleep, not REM sleep.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the EEG rhythms during sleep stages can vary between individuals and can be influenced by factors such as sleep disorders, medications, and neurological conditions. A thorough understanding of EEG patterns during different sleep stages is crucial for accurate diagnosis and management of sleep-related disorders.

✓ Correct Answer: A. ab.