Which sleep stage is characterized by sleep spindles and K-complexes?

Which sleep stage is characterized by sleep spindles and K-complexes?

• A. N1 sleep
• B. N2 sleep
• C. REM sleep
• D. N3 sleep

Answer: (B)

Spindles and K-complexes are the hallmark features of N2 non-REM sleep. In this stage, you see brief bursts of 12–14 Hz activity called sleep spindles, along with large, sharp K-complex waves that can occur spontaneously or in response to stimuli. These features help protect sleep from external arousal and support memory processes as sleep deepens from lighter to deeper non-REM stages. Other stages have different signatures: N1 shows lighter, theta-dominated activity with little to no spindles or K-complexes; N3 is dominated by delta waves indicating deep slow-wave sleep; REM sleep features rapid eye movements and a distinct, more mixed-frequency pattern with little to no spindles or K-complexes.

Spindles and K-complexes are the hallmark features of N2 non-REM sleep. In this stage, you see brief bursts of 12–14 Hz activity called sleep spindles, along with large, sharp K-complex waves that can occur spontaneously or in response to stimuli. These features help protect sleep from external arousal and support memory processes as sleep deepens from lighter to deeper non-REM stages.

Other stages have different signatures: N1 shows lighter, theta-dominated activity with little to no spindles or K-complexes; N3 is dominated by delta waves indicating deep slow-wave sleep; REM sleep features rapid eye movements and a distinct, more mixed-frequency pattern with little to no spindles or K-complexes.