1. Electrophysiological Characteristics
EEG Activity: During REM sleep, the brain exhibits mixed-frequency activity that closely resembles the awake state. This is typically low-amplitude, high-frequency brainwaves, particularly in the frontal regions of the brain.
Eye Movements: The most defining feature of REM sleep is the rapid eye movements. These movements are caused by the positive charge of the cornea. As the eyes move, they generate electrical activity that creates opposing signals on the EEG. When you look to the right, the cornea of the right eye moves closer to the right frontal electrode (F8), causing a positive wave, while the left eye moves away from the left frontal electrode (F7), creating a negative wave.
2. Muscle Atonia
Muscle Paralysis: One of the most important features of REM sleep is muscle atonia (paralysis). This is a protective mechanism that prevents the sleeper from physically acting out their dreams. While the brain is highly active, the body remains still, preventing potentially harmful movements.
3. Physiological Changes
Heart Rate and Breathing: During REM sleep, heart rate and breathing can become irregular, with fluctuations that vary in intensity and frequency. These fluctuations are generally mild but can be more pronounced in individuals with certain health conditions.
Breathing Patterns: Breathing may become faster and shallower, reflecting the brain’s increased activity during REM sleep.
4. Role in Sleep and Cognition
Dreaming: REM sleep is the stage most associated with vivid dreaming. The increased brain activity and mixed-frequency patterns are thought to be linked to the creation and processing of dreams.
Memory Consolidation: REM sleep plays an essential role in the consolidation of memories, particularly for procedural and emotional memories. It helps in the processing of information learned during the day, aiding in both long-term retention and emotional regulation.
Emotional and Cognitive Processing: REM sleep is thought to be important for emotional regulation and cognitive functions, helping to process and integrate emotions from daily experiences.
5. Sleep Cycle
REM sleep usually starts about 90 minutes after falling asleep and recurs multiple times throughout the night in cycles that become longer as the night progresses. A typical adult experiences several REM cycles per night, each lasting anywhere from 5 to 45 minutes.
In summary, REM sleep is a crucial stage of the sleep cycle, marked by unique physiological and neurological characteristics, including rapid eye movements, irregular heart rate and breathing, muscle atonia, vivid dreams, and a key role in memory and emotional processing.