Physiology, K Complex

Excerpt

Sleep is a swiftly reversible state of decreased metabolism, responsiveness and, motor activity, which is broadly categorized into rapid eye movement (REM) and non-rapid eye movement (NREM). The NREM sleep phase again subdivides into stage N1, stage N2, and stage N3. The K-Complex is a waveform identified on electroencephalography (EEG), which primarily occurs during Stage 2 (N2) of NREM sleep, along with sleep spindles, which make up the two distinct features seen in this stage.

The K-complex (KC) is a sharp, well-delineated, high-voltage, biphasic wave that lasts for more than 0.5 seconds and has been termed as the largest event in a healthy human EEG. On EEG, it was described by Laurino et al. as having a short positive voltage peak, which is usually at 200 milliseconds, followed by a large negative complex at around 550 milliseconds and finally, a long-lasting positive peak at 900 milliseconds. However, the initial short positive peak may not always be present. The occurrence of K-complexes may be spontaneous (spontaneous K-complex [SKC]), as a response to an internal stimulus such as a respiratory interruption or in response to an external stimulus like a touch on the skin (evoked K-complex [EKC]). Though K-complexes are generated in widespread areas of the cortex, they are seen maximally over the frontal and superior frontal cortices.