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      Sleep spindles in rats with absence epilepsy


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          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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          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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              Grouping of spindle activity during slow oscillations in human non-rapid eye movement sleep.

              Based on findings primarily in cats, the grouping of spindle activity and fast brain oscillations by slow oscillations during slow-wave sleep (SWS) has been proposed to represent an essential feature in the processing of memories during sleep. We examined whether a comparable grouping of spindle and fast activity coinciding with slow oscillations can be found in human SWS. For negative and positive half-waves of slow oscillations (dominant frequency, 0.7-0.8 Hz) identified during SWS in humans (n = 13), wave-triggered averages of root mean square (rms) activity in the theta (4-8 Hz), alpha (8-12 Hz), spindle (12-15 Hz), and beta (15-25 Hz) range were formed. Slow positive half-waves were linked to a pronounced and microV (23.4%; p < 0.001, with reference to baseline) at the midline central electrode (Cz). In contrast, spindle activity was suppressed during slow negative half-waves, on average by -0.65 +/- 0.06 microV at Cz (-22%; p < 0.001). An increase in spindle activity 400-500 msec after negative half-waves was more than twofold the increase during slow positive half-waves (p < 0.001). A similar although less pronounced dynamic was observed for beta activity, but not for alpha and theta frequencies. Discrete spindles identified during stages 2 and 3 of non-rapid eye movement (REM) sleep coincided with a discrete slow positive half-wave-like potential preceded by a pronounced negative half-wave (p < 0.01). These results provide the first evidence in humans of grouping of spindle and beta activity during slow oscillations. They support the concept that phases of cortical depolarization during slow oscillations, reflected by surface-positive (depth-negative) field potentials, drive the thalamocortical spindle activity. The drive is particularly strong during cortical depolarization, expressed as surface-positive field potentials.

                Author and article information

                Sleep Spindles & Cortical Up States
                Sleep Spindles & Cortical Up States
                Akadémiai Kiadó (Budapest )
                11 November 2017
                : 1-10
                [ 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
                © 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.

                : 26 August 2017
                : 22 September 2017
                Page count
                Figures: 6, Tables: 0, Equations: 0, References: 71, Pages: 10
                ORIGINAL PAPER

                Evolutionary Biology,Medicine,Psychology,Educational research & Statistics,Social & Behavioral Sciences
                spike–wave discharges,animal model,EEG analysis,time–frequency analysis,absence epilepsy,sleep spindles


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