In which stage of sleep do sleep spindles occur?

Sleep spindles are characteristic brainwaves that occur primarily during Stage 2 non-REM sleep. This stage of sleep is critical for memory consolidation and is marked by distinctive wave patterns observed on an electroencephalogram (EEG). During Stage 2, the brain displays bursts of oscillatory brain activity, known as sleep spindles, which typically last for about 0.5 to 2 seconds.

These spindles are believed to play a role in sensory processing and in the stabilization of sleep. Stage 2 also encompasses other significant features, such as K-complexes, which serve as a protective mechanism that helps to inhibit arousal to external stimuli, allowing sleep continuity.

In contrast, the other stages of sleep do not prominently feature sleep spindles. Stage 1 consists mainly of light sleep and transitional sleep with theta waves, Stage 3 is known for slow-wave sleep characterized by delta waves, and REM sleep, where vivid dreams occur, is marked by a different pattern of brain activity altogether, often resembling wakefulness.