The structure of sleep

Polysomnography reveals a structured progression of sleep stages, each with distinct brain and body activity. Stage 1 is transitional, with rolling eye movements. Stage 2, true sleep, features K-complexes and spindles. Stages 3 and 4 are deep sleep, marked by high amplitude delta waves. After deep sleep, REM sleep occurs, characterized by rapid eye movements and muscle relaxation. Understanding these stages is crucial for exploring sleep's relationship with brain functions, especially memory.

Explain the differences between stage 3 and stage 4 sleep.

What is rapid eye movement (REM) sleep and how does it differ from slow wave sleep?