What phase of sleep do sleep spindles occur?

Sleep spindles are characteristic brainwave patterns that occur primarily during Stage 2 of non-REM sleep. They are defined as bursts of oscillatory brain activity that typically last for about 0.5 to 2 seconds and represent a period of neural synchronization. The presence of sleep spindles is associated with the processing and consolidation of memory, as well as a deeper state of physiological relaxation and sleep maintenance.

During Stage 1 sleep, which is a light sleep phase, and Stage 3 sleep, also known as deep sleep or slow-wave sleep, different brain activity patterns are predominant. Specifically, Stage 1 is primarily characterized by theta waves, while Stage 3 shows delta waves. REM sleep, on the other hand, is marked by rapid eye movements and a brain wave pattern that more closely resembles wakefulness, which also does not include sleep spindles.

Thus, the occurrence of sleep spindles is a clear indication of Stage 2 sleep, reflecting its unique role in the sleep cycle and overall restorative processes during sleep.