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Science 22 May 2009:
Vol. 324. no. 5930, pp. 1084 - 1087
DOI: 10.1126/science.1169626
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Reports

The Human K-Complex Represents an Isolated Cortical Down-State

Sydney S. Cash,1,*,{dagger} Eric Halgren,2,* Nima Dehghani,2 Andrea O. Rossetti,5 Thomas Thesen,3 ChunMao Wang,3 Orrin Devinsky,3 Ruben Kuzniecky,3 Werner Doyle,3 Joseph R. Madsen,4 Edward Bromfield,5 Loránd Eross,6 Péter Halász,7,9 George Karmos,8,9 Richárd Csercsa,8 Lucia Wittner,6,8 István Ulbert6,8,9,*

The electroencephalogram (EEG) is a mainstay of clinical neurology and is tightly correlated with brain function, but the specific currents generating human EEG elements remain poorly specified because of a lack of microphysiological recordings. The largest event in healthy human EEGs is the K-complex (KC), which occurs in slow-wave sleep. Here, we show that KCs are generated in widespread cortical areas by outward dendritic currents in the middle and upper cortical layers, accompanied by decreased broadband EEG power and decreased neuronal firing, which demonstrate a steep decline in network activity. Thus, KCs are isolated "down-states," a fundamental cortico-thalamic processing mode already characterized in animals. This correspondence is compatible with proposed contributions of the KC to sleep preservation and memory consolidation.

1 Department of Neurology, Epilepsy Division, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
2 Departments of Radiology, Neurosciences, and Psychiatry, University of California at San Diego, San Diego, CA 92093, USA.
3 Comprehensive Epilepsy Center, New York University School of Medicine, New York, NY 10016, USA.
4 The Children’s Hospital, Boston, MA 02115, USA.
5 Brigham and Women’s Hospital, Boston, MA 02115, USA.
6 National Institute of Neurosurgery, H-1145 Budapest, Hungary.
7 National Institute of Psychiatry and Neurology, Epilepsy Center, H-1145 Budapest, Hungary.
8 Institute for Psychology, Hungarian Academy of Sciences, H-1394 Budapest, Hungary.
9 Péter Pázmány Catholic University, Department of Information Technology, H-1083 Budapest, Hungary.

* These authors contributed equally to this work.

{dagger} To whom correspondence should be addressed. E-mail: scash{at}partners.org

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Spatial characterization of interictal high frequency oscillations in epileptic neocortex.
C. A. Schevon, A. J. Trevelyan, C. E. Schroeder, R. R. Goodman, G. McKhann Jr, and R. G. Emerson (2009)
Brain 132, 3047-3059
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Science. ISSN 0036-8075 (print), 1095-9203 (online)