Maximum a posteriori estimation of change points in the EEG

A new approach for EEG segmentation is introduced. This is based on a methodology for optimal segmentation of non-stationary signals derived from the maximum a posteriori estimation principle. It is a model-based, not sequential approach that allows for segmentation at different resolution levels. The features of the methodology are illustrated by its application to EEG recordings containing several types of spectral changes due to normal and pathological variations of spontaneous brain rhythmic activities, as well as physiological artifacts.     

Rhythmic components of the EEG of 6-month-old children

Spectral EEG characteristics were studied in 12 six-month healthy children in a state of attention, attracted by visual stimuli and also at lowering of the level of visual afferentation and in drowsiness. 12 parts of EEG records free from artefacts were used, with analysis epoch 5 s and discretion frequency 100 counts/s. Three independent rhythmic EEG components have been revealed in alertness state, corresponding by criteria of functional reactivity and topographic localization to theta, alpha and mu EEG rhythms of the adult man. It is suggested that formation of dominating EEG rhythm with age occurs due to changes in dominant relations of the key rhythmic successions with independent genesis.     

Functional interrelations of brain structures in the cat during the generation of rhythmic activity. III. Cluster analysis of rhythmic indices

The functional interrelationships of the brain structures of freely moving cats in generation of rhythmic EEG activity during the states of drowsiness and light sleep were evaluated using the claster analysis of mean values indexes of rhythms in different structures as well as correlation coefficients between them in time. It was shown that according these parameters visual cortical areas and lateral geniculate body appeared in different clusters. Lateral geniculate body suggested not to be the only pacemaker of EEG rhythms in visual cortex. The wide convergence of subcortical inputs to the visual cortex and possibility of autonomic generation of EEG rhythms at the cortical level are discussed as putative mechanisms of dissociation of EEG activities in visual cortex and thalamus.     

A genetic study of the human low-voltage electroencephalogram

Summary The studied phenotype, the low-voltage electroencephalogram (LVEEG), is characterized by the absence of an alpha rhythm from the resting EEG. In previous studies, evidence was found for a simple autosomal-dominant mode of inheritance of the LVEEG. Such a polymorphism in brain function can be used as a research model for the stepwise elucidation of the molecular mechanism involved in those aspects of neuronal activity that are reflected in the EEG. Linkage with the variable number of tandem repeats (VNTR) marker CMM6 (D20S19) and localization of an LVEEG (EEGV1) gene on 20q have previously been reported, and genetic heterogeneity has been demonstrated. This latter result has been corroborated by studing new marker (MS214). The phenotype of the LVEEG is described here in greater detail. Its main characteristic is the absence of rhythmic alpha activity, especially in occipital leads, whereas other wave forms such as beta or theta waves may be present. Analysis of 17 new families (some of them large), together with 60 previously described nuclear families, supports the genetic hypothesis of an autosomal-dominant mode of inheritance. Problems connected with the analysis of linkage heterogeneity, exclusion mapping, and the study of multipoint linkage are discussed. A possible explanation of the localization of LVEEG in the close vicinity of another gene influencing synchronization of the normal EEG, the gene for benign neonatal epilepsie, is given.     

Detection of moments of operation of functional units in the human cortex using a new method of EEG analysis]

A new approach to EEG processing was proposed. The method allows the poorly predicted points on an EEG recording to be found, which are interpreted as the moments when certain functional units of the brain are engaged or disengaged. The functional units may be probably represented by columns or supercolumns. The method was tested in EEG recordings when the visual illusions were induced in a subject by a rhythmic photostimulation. The method seems to be rather promising.     

Sleep-Stage Correlates of Hippocampal Electroencephalogram in Primates

It has been demonstrated in the rodent hippocampus that rhythmic slow activity (theta) predominantly occurs during rapid eye movement (REM) sleep, while sharp waves and associated ripples occur mainly during non-REM sleep. However, evidence is lacking for correlates of sleep stages with electroencephalogram (EEG) in the hippocampus of monkeys. In the present study, we recorded hippocampal EEG from the dentate gyrus in monkeys overnight under conditions of polysomnographical monitoring. As result, the hippocampal EEG changed in a manner similar to that of the surface EEG: during wakefulness, the hippocampal EEG showed fast, desynchronized waves, which were partly replaced with slower waves of intermediate amplitudes during the shallow stages of non-REM sleep. During the deep stages of non-REM sleep, continuous, slower oscillations (0.5–8 Hz) with high amplitudes were predominant. During REM sleep, the hippocampal EEG again showed fast, desynchronized waves similar to those found during wakefulness. These results indicate that in the monkey, hippocampal rhythmic slow activity rarely occurs during REM sleep, which is in clear contrast to that of rodents. In addition, the increase in the slower oscillations of hippocampal EEG during non-REM sleep, which resembled that of the surface EEG, may at least partly reflect cortical inputs to the dentate gyrus during this behavioral state.     

Ontogenetic analysis of the EEG-activation reaction in children

Frequency characteristics of EEG-reaction have been analysed in children of 3-10 years in the process of realization of the orienting reflex to sound stimuli. An enhancement of theta- and alpha-oscillations has been found in such conditions which becomes less pronounced to 9-10 years. In the last age group, the reaction of blockade of the basic rhythm of the background EEG (alpha-oscillations of 10 Hz) is formed, combined with local enhancement of other rhythmic components of this frequency range. Functional significance of different forms of EEG activation reaction has been determined. The question is discussed of functional heterogeneity of rhythmic components of the alpha-range and their differential involvement in the reaction reflecting complex mechanisms of cortical activation.     

Dynamics of the Adolescent EEG Parameters with Changes in the CNS Functional State (Relaxation) Influenced by Rhythmic Acoustic Stimulation

Age-related specific features of the regulation of the CNS functional state (relaxation) were studied in adolescents between the ages of 14 and 15 years using 6-Hz rhythmic stimulation. The dynamics of the EEG findings (spectral power density, coherence functions) in the quiet wakefulness–relaxation–initial-state cycle was analyzed. The dynamics of the functional state was controlled by changes in the electrodermal resistance (EDR). The data showed that the studied group of adolescents was heterogeneous by the effectiveness of self-regulation: the majority was characterized by marked shifts whose distribution character was close to normal; the others, by mild EDR changes. It was shown that, with the use of rhythmic stimulation, relaxation shifts were more marked than those induced by common psychotherapeutic techniques. The basic relaxation changes in the EEG parameters are related to changes in the coherence function values, i.e., increases in its values, especially those of distant relations (with the focus) of significant connections in the frontal regions. The rate of the occurrence of relaxation changes in the coherence values is substantially higher in the low-frequency band (5 to 7 Hz) than in the EEG -band, constituting 20 to 50% in terms of different relations. The revealed specific features of the relaxation dynamics of the EEG parameters are analyzed in the age-related aspect. The influence of higher structures of the CNS and puberty-related rearrangements in the system of neuroendocrine regulation on the effectiveness of the regulatory function is discussed.     

Daily rhythmic behaviors and thermoregulatory patterns are disrupted in adult female MeCP2-deficient mice

Mutations in the X-linked gene encoding Methyl-CpG-binding protein 2 (MECP2) have been associated with neurodevelopmental and neuropsychiatric disorders including Rett Syndrome, X-linked mental retardation syndrome, severe neonatal encephalopathy, and Angelman syndrome. Although alterations in the performance of MeCP2-deficient mice in specific behavioral tasks have been documented, it remains unclear whether or not MeCP2 dysfunction affects patterns of periodic behavioral and electroencephalographic (EEG) activity. The aim of the current study was therefore to determine whether a deficiency in MeCP2 is sufficient to alter the normal daily rhythmic patterns of core body temperature, gross motor activity and cortical delta power. To address this, we monitored individual wild-type and MeCP2-deficient mice in their home cage environment via telemetric recording over 24 hour cycles. Our results show that the normal daily rhythmic behavioral patterning of cortical delta wave activity, core body temperature and mobility are disrupted in one-year old female MeCP2-deficient mice. Moreover, female MeCP2-deficient mice display diminished overall motor activity, lower average core body temperature, and significantly greater body temperature fluctuation than wild-type mice in their home-cage environment. Finally, we show that the epileptiform discharge activity in female MeCP2-deficient mice is more predominant during times of behavioral activity compared to inactivity. Collectively, these results indicate that MeCP2 deficiency is sufficient to disrupt the normal patterning of daily biological rhythmic activities.     

The phenomenon of the functional dissolution of the wakefulness-sleep cycle in white rats under the influence of immobilization]

Studies have been made on functional dissolution of the sleep cycle in albino rats due to immobilization of various duration. It was shown that 1-day immobilization increases microactivational representation in the EEG, facilitates rhythmic movements of the lower jaw, affects relative duration of the diurnal and nocturnal sleep, increases sleep fragmentation, and in some of the animals decreases the EEG amplitude. It is suggested that strong stress results in the return of sleep mechanisms to a more ancient level.     

Formation of the functional organization of the cerebral cortex at rest in young schoolchildren varying in the maturity of cerebral regulatory systems: I. Analysis of EEG spectral characteristics in the state of rest

Spectral correlation analysis of the EEG was used to study the organization of the rhythmic electrical activity (EA) of the cerebral cortex in normal children aged seven to eight and nine to ten years and children with the two types of functional immaturity of cerebral regulatory systems most common at this age, namely, fronto-thalamic regulatory system immaturity (IFTS) and brainstem nonspecific activation system immaturity (deficiency) (DNA). Statistical comparison (ANOVA) of these groups of children with respect to the absolute and relative α-and ?-band spectral powers of the background EEGs of 12 cortical areas showed the specific features of the effects of functional immaturity of regulatory systems at different levels on the cortical rhythmic EA pattern at rest. DNA led to a significant increase in the absolute spectral power of α and ? waves recorded in all derivations in both age groups, which indicated a generalized decrease in cortex activation in these children. IFTS caused a significant decrease in the relative strength of α waves and an increase in the strength of ? waves. Taking into account the results of ontogenetic studies, this may be regarded as evidence for a relative underdevelopment of cortical rhythm-generating networks. The absolute spectral powers of both α and ? waves were decreased in all groups of children by nine to ten years of age, which indicated that nonspecific activation was enhanced in the age interval studied. Significant changes were observed in children with functional immaturity of regulatory systems. In children with DNA, the age-related increase in cortex activation was expressed as a significant increase in the α-rhythm peak frequency. In children with IFTS, by nine to ten years of age, both the absolute and relative strengths of ? waves were decreased in most cortical areas studied, which may be regarded as the progressive formation of cortical rhythm-generating mechanisms.     

节律性听觉刺激下的神经振荡同步化及其应用

大脑的感觉、情绪、认知等功能与其神经振荡模式有密切的联系。通过施加节律性刺激可以调控大脑的神经振荡模式,进而影响个体感受、情绪状态和认知功能等。与近年来常见的非侵入性电刺激和磁刺激相比,同样依赖于外部刺激输入的节律性感觉刺激具有成本低、易操作等优点,被认为是一种极具潜力的神经调控手段。本文以节律性听觉刺激为例,系统综述了不同类型的节律性听觉刺激如何影响大脑的神经振荡模式,进而影响相关状态和功能;并通过总结外部节律性听觉刺激对个体感知觉、情绪与认知功能的影响,讨论其生理机制和应用前景。     

Vagal afferents and EEG rhythms in the Sl area in anesthetized cats: similarities between responses to electrical and chemical (phenyldiguanide) stimulations

In anesthetized, artificially ventilated cats with open chest, bilateral stimulation of all afferent vagal fibres (pulse duration: 800 microseconds, 30 Hz, train duration 30 to 40 s) produced marked changes in the spontaneous EEG activities in the primary somatosensory cortex (Sl area). They were characterized by depressed background rhythms, with a tendency to desynchronization, decreased amplitude and number of spindles, with altered pattern, and/or evoked sustained fast rhythmic activities. These effects occurred within 1 to 5 sec during vagal stimulation. On the contrary, the EEG response was weaker or absent when only myelinated vagal afferents were stimulated (100 microseconds). I.v. injection of phenyldiguanide (PDG), used for stimulation of unmyelinated vagal sensory fibres and mainly of pulmonary afferents, induced EEG changes within the first 30 s, similar to those observed during electrical vagal stimulation. These EEG responses were unrelated to the induced hypotension. Cervical bivagotomy produced persistent changes in EEG activity, with enhancement of the magnitude, duration and number of spindles, which resembled the delayed effects induced by PDG. The present results obtained with three test agents (electrical or chemical vagal stimulation and bivagotomy) demonstrated that, in cats, vagal afferent information interacted with the spontaneous EEG rhythms in the Sl area.     

The effect of a high-intensity radiation exposure on the brain function of monkeys. The postradiation changes in the EEG response to rhythmic photostimulation]

In experiments with monkeys (Macaca fascicularis) it has been shown that whole-body irradiation with a dose of 45 Gy (6.5 Gy/s) causes considerable changes in the EEG response to rhythmic photostimulation (PS). These changes are: reduction of the desynchronizing effect of PS with regard to a background rhythmicity; decrease in the reception rate of the rhythms of light flashes (RLF); narrowing of the RLF frequency range; and increase in the reaction momentum. The postirradiation changes in the EEG response to PS are considered as a manifestation of inhibition of the cortex functional activity and impairment of sensory information processing in the brain.     

New aspects of the neurophysiological mechanism of the action of nootropic preparations

The influence of nootropic drugs on EEG spectral power of the cortex and hippocamp was studied in resting rats. All these drugs had a specific action on EEG spectral power, causing an increase and stabilization of maximum basic distribution peak of the EEG spectral power. Such action may be attributed to better organization of rhythmic activity in theta-range. The drugs also decreased interhemispheric asymmetry of the cortical and hippocampal EEG. The authors suggest that the increase and improvement of the basic rhythmic activity in the brain and an increased level of distant (spatial) synchronization form the basis for the nootropic drug effect.     

Existence of respiratory interneurons in the cervical spinal cord of the rabbit

A spinal "respiration" generator has been shown to fire phrenic motoneurones in rhythmic bursts. It is very likely driven through bulbo-spinal inspiratory neurones in intact preparations. Although no direct evidence for respiratory interneurones at the C4-C5 spinal levels has been obtained so far (except for Renshaw cells ), it is currently believed that only few inspiratory inputs to the phrenic motoneurones are transmitted monosynaptically from the medulla. We have tried here to record spinal interneuronal respiratory activities in decorticate, unanaesthetized, vagotomized and curarized rabbit preparations. Different functional categories of interneurones could be identified at the C4-C5 spinal levels: inspiratory and expiratory interneurons with various discharge patterns which rather well correspond to the functional categories of inspiratory and expiratory bulbo-spinal neurones described by Bianchi and Richter. In addition, multiunit inspiratory bursting could be followed over several 100 microns during each electrode penetration. The different categories of interneurones were encountered laterally from 700 to 1,000 microns, at depths ranging from 300 to 500 microns dorsally to the phrenic nucleus, down to the nucleus itself. These results indicate that part of the medullary inspiratory drive is channelled via spinal cord interneurones; they also suggest that an inhibition of phrenic motoneurones from the bulbo-spinal expiratory drive takes place via interneurones.     

Functional interrelation of the brain structures of the cat during the generation of rhythmic activity. I. The frequency characteristics of the electroencephalogram

The similarity of frequency parameters of electroencephalograms (EEG) recorded from visual, associative and sensorimotor cortical area, caudate nucleus and several thalamic nuclei have been analysed using the period analysis of EEG and cluster analysis of data obtained to clarify the functional interrelationships between these parts of the brain during generation of rhythmic activity of different types. Functional interrelationships between brain structures in freely moving cats during the states of drowsiness and slow-wave sleep have been shown to differ from "classical" thalamo-cortical pacemaker relations.     

Voluntary regulation of the functional state and its influence on the effectiveness of cognitive activity during adolescence

We have analyzed the impact of voluntary relaxation on the functional organization and the effectiveness of the voluntary prestimulus attention in performing cognitive tasks in adolescents at the ages of 12–13 and 13–14 years. The effectiveness of cognitive task performance (audio-verbal short-term memory) was estimated on the basis of the number of correctly remembered words. We have found that both age groups are characterized by reduced capacity for voluntary relaxation and its impact on the effectiveness of cognitive task performance. The analysis of the coherence function of EEG rhythmic components in a situation of voluntary attention focused on the performance of cognitive tasks showed no significant change in the interaction of the prefrontal cortex with other cortical areas during the switch from quiet wakefulness or post-relaxation state to the preparation to perform the task, which is typical of adults and young children. Our findings can be a result of sub-optimal functioning of voluntary regulation mechanisms and organization of activities during adolescence.     

Concurrent Electroencephalography Recording During Transcranial Alternating Current Stimulation (tACS)

Oscillatory brain activities are considered to reflect the basis of rhythmic changes in transmission efficacy across brain networks and are assumed to integrate cognitive neural processes. Transcranial alternating current stimulation (tACS) holds the promise to elucidate the causal link between specific frequencies of oscillatory brain activity and cognitive processes. Simultaneous electroencephalography (EEG) recording during tACS would offer an opportunity to directly explore immediate neurophysiological effects of tACS. However, it is not trivial to measure EEG signals during tACS, as tACS creates a huge artifact in EEG data. Here we explain how to set up concurrent tACS-EEG experiments. Two necessary considerations for successful EEG recording while applying tACS are highlighted. First, bridging of the tACS and EEG electrodes via leaking EEG gel immediately saturates the EEG amplifier. To avoid bridging via gel, the viscosity of the EEG gel is the most important parameter. The EEG gel must be viscous to avoid bridging, but at the same time sufficiently fluid to create contact between the tACS electrode and the scalp. Second, due to the large amplitude of the tACS artifact, it is important to consider using an EEG system with a high resolution analog-to-digital (A/D) converter. In particular, the magnitude of the tACS artifact can exceed 100 mV at the vicinity of a stimulation electrode when 1 mA tACS is applied. The resolution of the A/D converter is of importance to measure good quality EEG data from the vicinity of the stimulation site. By following these guidelines for the procedures and technical considerations, successful concurrent EEG recording during tACS will be realized.