The Power of Sleep - Lesson 1 - The Science of Sleep: NREM and REM
Sleep is composed of two primary phases: **Non-Rapid Eye Movement (NREM)** sleep and **Rapid Eye Movement (REM)** sleep. Each plays a unique role in supporting physical and mental health. During NREM sleep, which accounts for roughly 75–80% of the night, your body moves through three progressive stages.
Stage 1: Is light sleep, often lasting just a few minutes as you transition from wakefulness.
Stage 2: This marks the beginning of true sleep. During this stage, your heart rate slows, body temperature drops, and your brain begins to produce unique patterns of brain activity known as sleep spindles and K-complexes.
Sleep spindles are short bursts of rapid brain waves that help protect your sleep by blocking out external noises and disturbances, allowing you to stay asleep more easily.
K-complexes are brief, high-amplitude brain waves that occur in response to external stimuli, like a sound or movement. They act as a built-in "sleep shield," helping your brain decide whether to stay asleep or wake up.
Both of these features are also believed to play an important role in processing and storing new information, supporting memory consolidation and learning while you rest.
Stage 3: Also known as slow-wave sleep or deep sleep, is where physical recovery and repair happen. This is when your body produces growth hormone, repairs tissues, and fortifies the immune system.
**REM sleep**, on the other hand, is where most dreaming takes place. It is characterized by rapid eye movement, increased brain activity, and temporary muscle paralysis to prevent you from physically acting out your dreams. REM sleep is essential for brain function, it helps process emotions, organize memories, and foster creative problem-solving. As the night progresses, REM periods become longer, especially during the early morning hours. Without enough REM sleep, your ability to focus, manage stress, and regulate emotions may suffer significantly.
The Sleep Cycle
A complete sleep cycle typically lasts 90-110 minutes. Throughout a healthy night’s rest, you’ll experience four to six of these cycles. The cycle begins with NREM sleep, moving through the three stages, and ends with REM. Each cycle has a different balance of NREM and REM sleep.
Early in the night, deep sleep (Stage 3) dominates, which is vital for physical recovery. As the night goes on, REM sleep becomes more prevalent. This cycling is critical; it’s not just about the number of hours you sleep, but how many full cycles your body completes. Interrupting the sleep cycle (due to waking up often, stress, alcohol, or light exposure) robs the body of vital recovery time.
