What physiological response is indicated by the presence of K-complexes?

The presence of K-complexes is indicative of brain arousal, particularly during sleep. K-complexes are sharp, high-amplitude waves that occur in response to external stimuli and are considered an essential part of sleep architecture. They can be thought of as markers of the brain's ability to process stimuli while remaining in a sleep state, thereby reflecting momentary disturbances or threats to sleep continuity.

While K-complexes can appear during non-REM sleep and are often associated with deep sleep stages, their primary function is to aid the brain in maintaining sleep despite potentially disruptive factors. This ability to arouse the brain enhances the chances of returning to stable sleep rather than fully waking. The occurrence of K-complexes highlights how the brain remains responsive and active even during sleep, differentiating them from other sleep features like sleep spindles, which are primarily involved in sleep stability and memory consolidation.