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      Sleep spindles in rats with absence epilepsy

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          Abstract

          Absence epilepsy is an idiopathic generalized non-convulsive type of epilepsy associated with aberrant activity in the thalamocortical network. The common neuronal network mechanism of spike–wave discharges (a manifestation of absence epilepsy) and sleep spindles suggests a close relationship between them. This paper overviews electroencephalographic (EEG) properties of anterior sleep spindles in a genetic Wistar Albino Glaxo from Rijswijk (WAG/Rij) rat model of absence epilepsy. Epileptic discharges in WAG/Rij rats appear spontaneously, and their incidence increases with age. In epileptic rats, time–frequency profile of sleep spindles distinguished from that in non-epileptic subjects by shorter duration, lower intraspindle frequency, and contained less slow-wave components, etc. Some pro-epileptic modifications of spindle activity can also be observed in EEG in epileptic WAG/Rij rats.

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          Most cited references 65

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          Sleep spindles: an overview

          Sleep spindles are a distinctive EEG phasic feature of NREM sleep and are prevalent during stage 2 as compared to slow wave sleep. While the neurophysiological mechanisms of spindle generation, that involves thalamic and corticothalamic networks, have been recently delineated and are briefly reviewed, their definitive functional meaning still remains to be elucidated. This review summarizes the present knowledge on visually scored and automatically detected spindles, as well as the literature on EEG power in the sigma band. Among the factors known to affect sleep spindles and sigma activity, their intra-cycle temporal dynamics, their time-course across sleep cycles, the reciprocal relationship with delta activity, the effects of sleep deprivation, of circadian factors and of ageing, and their role in information processing have been discussed. Moreover, specific attention has been paid to the existence of functionally and topographically distinct slow- and fast-spindles, also taking into account the presence of large inter-individual differences. Nevertheless, several fundamental issues remain to be elucidated: the physiological mechanisms controlling age-related changes in spindle parameters; the role of melatonin as a spindle-promoting agent; the relationships between plastic mechanisms (after stroke, or as a consequence of learning) and modifications in spindle activity; the possibility of using some spindle parameters as an index of the severity of developmental disorders in abnormal maturational processes.
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            The function of the sleep spindle: a physiological index of intelligence and a mechanism for sleep-dependent memory consolidation.

            Until recently, the electrophysiological mechanisms involved in strengthening new memories into a more permanent form during sleep have been largely unknown. The sleep spindle is an event in the electroencephalogram (EEG) characterizing Stage 2 sleep. Sleep spindles may reflect, at the electrophysiological level, an ideal mechanism for inducing long-term synaptic changes in the neocortex. Recent evidence suggests the spindle is highly correlated with tests of intellectual ability (e.g.; IQ tests) and may serve as a physiological index of intelligence. Further, spindles increase in number and duration in sleep following new learning and are correlated with performance improvements. Spindle density and sigma (14-16Hz) spectral power have been found to be positively correlated with performance following a daytime nap, and animal studies suggest the spindle is involved in a hippocampal-neocortical dialogue necessary for memory consolidation. The findings reviewed here collectively provide a compelling body of evidence that the function of the sleep spindle is related to intellectual ability and memory consolidation. Copyright © 2010 Elsevier Ltd. All rights reserved.
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              Sleep spindles in humans: insights from intracranial EEG and unit recordings.

              Sleep spindles are an electroencephalographic (EEG) hallmark of non-rapid eye movement (NREM) sleep and are believed to mediate many sleep-related functions, from memory consolidation to cortical development. Spindles differ in location, frequency, and association with slow waves, but whether this heterogeneity may reflect different physiological processes and potentially serve different functional roles remains unclear. Here we used a unique opportunity to record intracranial depth EEG and single-unit activity in multiple brain regions of neurosurgical patients to better characterize spindle activity in human sleep. We find that spindles occur across multiple neocortical regions, and less frequently also in the parahippocampal gyrus and hippocampus. Most spindles are spatially restricted to specific brain regions. In addition, spindle frequency is topographically organized with a sharp transition around the supplementary motor area between fast (13-15 Hz) centroparietal spindles often occurring with slow-wave up-states, and slow (9-12 Hz) frontal spindles occurring 200 ms later on average. Spindle variability across regions may reflect the underlying thalamocortical projections. We also find that during individual spindles, frequency decreases within and between regions. In addition, deeper NREM sleep is associated with a reduction in spindle occurrence and spindle frequency. Frequency changes between regions, during individual spindles, and across sleep may reflect the same phenomenon, the underlying level of thalamocortical hyperpolarization. Finally, during spindles neuronal firing rates are not consistently modulated, although some neurons exhibit phase-locked discharges. Overall, anatomical considerations can account well for regional spindle characteristics, while variable hyperpolarization levels can explain differences in spindle frequency.
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                Author and article information

                Journal
                sscus
                SSCUS
                Sleep Spindles & Cortical Up States
                Sleep Spindles & Cortical Up States
                Akadémiai Kiadó (Budapest )
                11 November 2017
                :
                :
                : 1-10
                Affiliations
                [ 1 ] Institute of Higher Nervous Activity and Neurophysiology of Russian Academy of Sciences , Moscow, Russia
                Author notes
                [* ]Correspondence: Evgenia Sitnikova, Ph.D., D.Sc., Institute of Higher Nervous Activity and Neurophysiology of Russian Academy of Sciences, Butlerova str., 5A, Moscow 117485, Russia, E-mail: eu.sitnikova@ 123456gmail.com
                10.1556/2053.01.2017.004
                © 2017 The Author(s)

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium for non-commercial purposes, provided the original author and source are credited.

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                Figures: 6, Tables: 0, Equations: 0, References: 71, Pages: 10
                Categories
                ORIGINAL PAPER

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