Kkomplex

A K-complex, sometimes written as Kkomplex, is a distinctive waveform observed on electroencephalography (EEG) during sleep. It typically appears as a single, large deflection consisting of a sharp negative spike followed by a slower positive component, lasting several hundred milliseconds and reaching amplitudes on the order of 100 to 200 microvolts in central to frontal regions.

K-complexes occur predominantly during non-rapid eye movement sleep, especially stage N2. They can arise spontaneously or be elicited by external stimuli such as sounds or tactile input. In non-REM sleep, they occur with a density of about one per minute in N2, and their occurrence tends to decrease as sleep deepens toward slow-wave sleep.

Physiologically, K-complexes are generated by thalamo-cortical networks and are thought to reflect a transient arousal that briefly heightens cortical responsiveness before sleep is preserved. They are often followed by sleep spindles and are most prominently recorded in central and frontal EEG leads (for example Cz, C3, C4, and Fz).

Functionally and clinically, K-complexes are a defining feature of stage N2 sleep and serve as a marker of arousal threshold. They may play a role in processing external information during sleep and in memory-related consolidation processes. In routine sleep studies, the presence of K-complexes is typical of healthy sleep; abnormalities in their frequency, amplitude, or elicitation can be observed in various sleep or neurological conditions, including sleep disorders such as obstructive sleep apnea.

In summary, the K-complex is a characteristic N2 sleep waveform generated by thalamo-cortical activity, reflecting a brief arousal response that is quickly suppressed to maintain sleep continuity.