#01: What is Sleep?

Sleep architecture consists of two primary types: non-rapid eye movement (non-REM) sleep and rapid eye movement (REM) sleep. Non-REM sleep, subdivided into four stages of increasing depth, features powerful brain waves and sleep spindles that facilitate memory consolidation. These stages alternate with REM sleep in roughly 90-minute cycles, a rhythm observed across mammalian species. While the first half of the night is dominated by deep non-REM sleep, the second half shifts toward increased REM sleep, which is essential for dreaming and emotional processing. Cutting sleep short disproportionately impacts this second half, leading to a significant loss of REM sleep. Understanding this structural balance allows for the optimization of sleep schedules to ensure the brain receives the full spectrum of restorative benefits provided by each stage.