Đề thi VSTEP Reading B2 — The Science of Sleep Cycles

Although humans spend roughly one-third of their lives sleeping, the purpose of sleep remains one of biology's most enduring puzzles. Modern research has identified that sleep is not a single state but a complex cycle of distinct phases. A complete sleep cycle typically lasts about 90 minutes and consists of four stages. The first three stages are known as non-REM sleep, during which the body relaxes, heart rate slows, and brain activity decreases. The fourth stage, REM (Rapid Eye Movement) sleep, is when most dreaming occurs. During REM sleep, the brain becomes highly active, while the body's muscles remain essentially paralyzed. Interestingly, the body does not distribute these stages evenly throughout the night. The first half of sleep contains more deep non-REM stages, which are essential for physical recovery. The second half contains longer REM periods, which play a critical role in memory consolidation and emotional regulation. Understanding these patterns has practical implications. Sleep researchers now recommend that adults focus on sleep quality rather than just quantity, suggesting that completing four to five full cycles each night leads to better cognitive performance and overall health.