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J Neuropsychiatry Clin Neurosci. 2017 Summer;29(3):236-247. doi: 10.1176/appi.neuropsych.16060120. Epub 2017 Jan 25.

Focal Changes to Human Electrocorticography With Drowsiness: A Novel Measure of Local Sleep.

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From the Department of Neurology, University of Texas Medical School at Houston, Houston, Tex. (JDS, GK); the Department of Neurobiology and Anatomy, University of Texas Medical School at Houston, Houston, Tex. (JDS, MIC, BJH, CB, VD); Department of In Vivo Pharmacology, Merck Research Laboratories, West Point, Penn. (BJH); and the Vivian L. Smith Department of Neurosurgery, University of Texas Medical School at Houston, Houston, Tex. (NT).


Drowsiness may be defined as the progressive loss of cortical processing efficiency that occurs with time passing while awake. This loss of cortical processing efficiency is reflected in focal changes to the electroencephalogram, including islands of increased delta power concurrent with drop-offs in neuronal activity (i.e., focal cortical inactivity). The authors hypothesized that these focal changes are evidenced at individual electrodes by combination of increased instantaneous amplitude in delta band and decreased instantaneous frequency in theta-alpha band, permitting their categorization as "active" and "inactive." An analysis of records from six patients with refractory epilepsy undergoing video-electrocorticographic monitoring was conducted. Feature extraction and state classification on multiple recordings revealed focal changes consistent with the hypothesis, as well as progressively increased numbers of inactive electrodes with time awake. The implications of these findings on the study of sleep, and particularly local sleep, are discussed.


Biological Rhythms; Neurophysiology; Research Design and Methodology; Sleep

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