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eNeuro. 2015 Sep 17;2(4). pii: ENEURO.0028-15.2015. doi: 10.1523/ENEURO.0028-15.2015. eCollection 2015 Jul-Aug.

Distribution, Amplitude, Incidence, Co-Occurrence, and Propagation of Human K-Complexes in Focal Transcortical Recordings

Author information

1
Department of Neurosciences, University of California, San Diego , San Diego, California 92093.
2
Department of Radiology, University of California, San Diego , San Diego, California 92093.
3
Aix-Marseille Université , Marseille 13385, France ; INSERM, Institut de Neurosciences des Systèmes UMR 1106 , Marseille 13005, France ; Assistance Publique-Hôpitaux de Marseille, Timone Hospital , Marseille 13005, France.
4
Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Harvard University , Boston, Massachusetts 02114.
5
Department of Neurosciences, University of California, San Diego , San Diego, California 92093 ; Department of Radiology, University of California, San Diego , San Diego, California 92093 ; Department of Psychiatry, University of California, San Diego , San Diego, California 92093.

Abstract

K-complexes (KCs) are thought to play a key role in sleep homeostasis and memory consolidation; however, their generation and propagation remain unclear. The commonly held view from scalp EEG findings is that KCs are primarily generated in medial frontal cortex and propagate parietally, whereas an electrocorticography (ECOG) study suggested dorsolateral prefrontal generators and an absence of KCs in many areas. In order to resolve these differing views, we used unambiguously focal bipolar depth electrode recordings in patients with intractable epilepsy to investigate spatiotemporal relationships of human KCs. KCs were marked manually on each channel, and local generation was confirmed with decreased gamma power. In most cases (76%), KCs occurred in a single location, and rarely (1%) in all locations. However, if automatically detected KC-like phenomena were included, only 15% occurred in a single location, and 27% occurred in all recorded locations. Locally generated KCs were found in all sampled areas, including cingulate, ventral temporal, and occipital cortices. Surprisingly, KCs were smallest and occurred least frequently in anterior prefrontal channels. When KCs occur on two channels, their peak order is consistent in only 13% of cases, usually from prefrontal to lateral temporal. Overall, the anterior-posterior separation of electrode pairs explained only 2% of the variance in their latencies. KCs in stages 2 and 3 had similar characteristics. These results open a novel view where KCs overall are universal cortical phenomena, but each KC may variably involve small or large cortical regions and spread in variable directions, allowing flexible and heterogeneous contributions to sleep homeostasis and memory consolidation.

KEYWORDS:

SEEG; depth recordings; k-complex; memory; sleep

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