Intracranial cortical localization of the human K-complex

ObjectiveThe K-complex was first identified in human sleep EEG more than 70 years ago, but the localization of its intracranial generators is an unresolved issue. In this study, K-complexes recorded using simultaneous scalp and intracranial EEG were analyzed to discover the intracranial distribution of the human K-complex.MethodsStereoelectroencephalographic recordings were performed in six patients with medically-refractory epilepsy. Full 10–20 scalp montages were used and intracranial macroelectrodes sampled medial, lateral and basal frontal and temporal cortices, medial and lateral parietal and occipital cortices, as well as the hippocampus and thalamus. Spontaneous K-complexes were visually identified in stage II sleep and averaged off-line.ResultsThe intracranial K-complex field was maximal over the anterior and superior aspects of the medial and lateral frontal lobe cortices, consistent with the frontal midline scalp EEG maximum. The frontal maximum surface-negative field was volume conducted as an inverted, positive field posteriorly and inferiorly, the polarity reversing laterally above the inferior temporal region and medially above the cingulate cortex.ConclusionsAs suggested by the scalp EEG topography, the intracranial distribution of the human K-complex is maximal over the anterior and superior frontal cortices. K-complex generation appears limited to cortical regions above the inferior temporal sulcus laterally, the cingulate sulcus medially and the parietooccipital junction posteriorly.SignificanceThe human K-complex is produced by synchronous cortical activity that appears maximal intracranially over the superior medial and lateral aspects of the frontal lobes. The cingulate cortex and functionally related mesial temporal structures appear uninvolved in human K-complex generation.