EEG correlates of hypnotic susceptibility based upon fast Fourier power spectral analysis

The purpose of the present study was to determine if there were differences between high and low hypnotic susceptible subjects based upon fast Fourier power spectral analysis of the EEG recorded both before and during hypnotic tasks from frontal-temporal and occipital-parietal locations. Significant differences were obtained based upon EEG recording electrode location, EEG frequency within six different frequency domains, and hypnotic tasks. However, no main effect differences were obtained based upon hypnotic susceptibility. In contrast to some evoked potential studies in which a few differences have been obtained based on hypnotic susceptibility the lack of any EEG differences in this study even when positive and negative hallucination tasks were employed may have implications for the role of the neocortex in mediating hypnotic phenomena.We would like to acknowledge Dr. Michael K. Smith for his help in developing the statistical analysis and for his help in transforming the linear data employed in the ANOVAs in this study.     

Localizing Movement-Related Primary Sensorimotor Cortices with Multi-Band EEG Frequency Changes and Functional MRI

Electroencephalographic (EEG) oscillations in multiple frequency bands can be observed during functional activity of the cerebral cortex. An important question is whether activity of focal areas of cortex, such as during finger movements, is tracked by focal oscillatory EEG changes. Although a number of studies have compared EEG changes to functional MRI hemodynamic responses, we can find no previous research that relates the fMRI hemodynamic activity to localization of the multiple EEG frequency changes observed in motor tasks. In the present study, five participants performed similar thumb and finger movement tasks in parallel EEG and functional MRI studies. We examined changes in five frequency bands (from 5–120 Hz) and localized them using 256 dense-array EEG (dEEG) recordings and high-resolution individual head models. These localizations were compared with fMRI localizations in the same participants. Results showed that beta-band (14–30 Hz) desynchronizations (power decreases) were the most robust effects, appearing in all individuals, consistently localized to the hand region of the primary motor cortex, and consistently aligned with fMRI localizations.     

Changes in human EEG alpha activity following exposure to two different pulsed magnetic field sequences

The present study investigates the effects of a weak (+/-200 microT(pk)), pulsed, extremely low frequency magnetic field (ELF MF) upon the human electroencephalogram (EEG). We have previously determined that exposure to pulsed ELF MFs can affect the EEG, notably the alpha frequency (8-13 Hz) over the occipital-parietal region of the scalp. In the present study, subjects (n = 32) were exposed to two different pulsed MF sequences (1 and 2, used previously) that differed in presentation rate, in order to examine the effects upon the alpha frequency of the human EEG. Results suggest that compared to sham exposure, alpha activity was lowered over the occipital-parietal regions of the brain during exposure to Sequence 1, while alpha activity over the same regions was higher after Sequence 2 exposure. These effects occurred after approximately 5 min of pulsed MF exposure. The results also suggest that a previous exposure to the pulsed MF sequence determined subjects' responses in the present experiment. This study supports our previous observation of EEG changes after 5 min pulsed ELF MF exposure. The results of this study are also consistent with existing EEG experiments of ELF MF and mobile phone effects upon the brain.     

Human electrophysiological and cognitive effects of exposure to ELF magnetic and ELF modulated RF and microwave fields: a review of recent studies

The investigation of weak (<500 microT), extremely low frequency (ELF, 0-300 Hz) magnetic field (MF) exposure upon human cognition and electrophysiology has yielded incomplete and contradictory evidence that MFs interact with human biology. This may be due to the small number of studies undertaken examining ELF MF effects upon the human electroencephalogram (EEG), and the associated analysis of evoked related potentials (ERPs). Relatively few studies have examined how MF exposure may affect cognitive and perceptual processing in human subjects. The introduction of this review considers some of the recent studies of ELF MF exposure upon the EEG, ERPs and cognitive and perceptual tasks. We also consider some of the confounding factors within current human MF studies and suggest some new strategies for further experimentation.     

Online Classification of Multiple Motor Imagery Tasks Using Filter Bank Based Maximum-a-Posteriori Common Spatial Pattern Filters

ObjectiveThe main objective of this paper is to propose a novel technique, called filter bank maximum a-posteriori common spatial pattern (FB-MAP-CSP) algorithm, for online classification of multiple motor imagery activities using electroencephalography (EEG) signals. The proposed technique addresses the overfitting issue of CSP in addition to utilizing the spectral information of EEG signals inside the framework of filter banks while extending it to more than two conditions.Materials and methodsThe classification of motor imagery signals is based upon the detection of event-related de-synchronization (ERD) phenomena in the μ and β rhythms of EEG signals. Accordingly, two modifications in the existing MAP-CSP technique are presented: (i) The (pre-processed) EEG signals are spectrally filtered by a bank of filters lying in the μ and β brainwave frequency range, (ii) the framework of MAP-CSP is extended to deal with multiple (more than two) motor imagery tasks classification and the spatial filters thus obtained are calculated for each sub-band, separately. Subsequently, the most imperative features over all sub-bands are selected and un-regularized linear discriminant analysis is employed for classification of multiple motor imagery tasks.ResultsPublicly available dataset (BCI Competition IV Dataset I) is used to validate the proposed method i.e. FB-MAP-CSP. The results show that the proposed method yields superior classification results, in addition to be computationally more efficient in the case of online implementation, as compared to the conventional CSP based techniques and its variants for multiclass motor imagery classification.ConclusionThe proposed FB-MAP-CSP algorithm is found to be a potential / superior method for classifying multi-condition motor imagery EEG signals in comparison to FBCSP based techniques.     

Cognitive brain–Computer interface and probable aspects of its practical application

A new type of brain-computer interface was elaborated. It considers a variety of brain activity parameters to determine the type of mental operation being performed at the moment. The corresponding algorithm previously developed in the lab was modified for real-time application. The possibility of interface application for cognitive skills training was investigated. In the proposed paradigm, as soon as the EEG spectral pattern was adequate for the current task, some clue to the solution was presented. As we supposed, such positive biofeedback should facilitate memorization of the current brain state. After just one learning session, the differences in EEG spectra, corresponding to two types of tasks, were concentrated in more narrow frequency ranges. It indicates a decrease in mental effort. Moreover, the majority of subjects succeeded in solving the tasks faster, which is evidence of increased efficiency. The developed interface could be used for the new type of training, based on objective features of brain activity.     

EEG beta and gamma powers when comparing certain psychophysiological states with normal and weakened electromyogram of facial muscles

With the advancement of contemporary techniques for studies of high-frequency electroencephalograms (EEGs), possible contamination of the EEG with the electromyogram (EMG) of pericranial muscles has raised more and more concern. The aim of the present study was to demonstrate if certain EEG correlates of mental activities can be revealed in a high-frequency scalp EEG in spite of EMG contamination. Nineteen healthy women who performed similar test tasks before and after cosmetic injections of Dysport in various facial regions for reduction of the activity of facial muscles took part in the study. Inductions of emotional states with different valences, memory storing, and extraction of verbal information were used in the test tasks. The default state of rest was examined as well. During performance of the tasks, parallel registrations of the EEG from the scalp surface (19 channels) and EMG from several facial muscles (6 channels) were carried out. Changes in the spectral power in β₂ and low γ frequency bands (18–40 Hz) in EEG- and EMG-derivations after Dysport injections were analyzed. Changes in the spectral power in the same bands in pairwise comparisons for the test tasks before and after Dysport injections were also analyzed separately. It was demonstrated that Dysport injections lead to reduction of the EMG power in areas of the injections and to reduction of EEG power in the frontal and temporal derivations. However, the EEG-correlates revealed when comparing different test tasks remained qualitatively invariable as for after and before Disport injections. These facts confirm that EMG makes a noticeable contribution to the electric activity registered from the scalp in the frequency ranges greater than 18 Hz. At the same time, one can see that at least in certain experimental situations the influence of EMG does not make impossible identification of EEG-correlates of mental activity with EEG registration from the head surface at least in the β₂ and low γ frequency bands (18–40 Hz).     

The reflection of different aspects of brain activation in the electroencephalogram: Quantitative electroencephalography of the states of rest with the eyes open and closed

The rest states with the eyes open (RSEO) and closed (RSEC) were subjected to quantitative EEG study as states similar in the pattern of mental activity and subjective assessments but different in the EEG pattern. The mean values of the spectral power and EEG coherence function were compared in 74 subjects for the following bands: Δ, ?, α₁, α₂, β₁, β₂, and γ. Upon the transition from the RSEC to the RSEO, the EEG local power significantly decreased over the whole cortex for the α, ?, and β bands. A simultaneous decrease in the EEG power in all the bands (including β and γ) was most pronounced (as judged by relative changes and tests of significance of difference) in the parietooccipital derivations immediately related to the cortical zones where an increase in the neuronal activity upon opening the eyes is most probable. A significant increase in the EEG power was observed only for the γ band in frontal derivations F ₃ and F ₄. Significant differences in the mean EEG coherence in the RSEO-RSEC comparison were present in many derivation pairs, especially in the α₂, β₁, β₂, and γ bands. For each of these bands, the number of differences determined on the basis of Fisher test was more than 70% of the maximum possible number. In the overwhelming majority of cases, the coherence was lower in the RSEO; however, in the caudal cortical zones, a higher coherence in the α₁, ?, and Δ bands in the RSEO was rather typical. The results confirmed that the two states under study differ in a number of averaged EEG parameters with high statistical significance and may be used as reference states during performance of tasks with the eyes open and closed, respectively. The differences between the RSEC and the RSEO may be caused by the fact that the RSEC is a functional state oriented predominantly to the analysis of internal information (internally oriented), and the RSEO, predominantly to the analysis of information coming from the outside (externally oriented). The pattern of the observed EEG differences points to a combination of effects both localized in the visual zone and reflecting changes in the network cortical activity, i.e., simultaneous, although nonuniform, changes over all the main zones of the cortex. Comparison of the results with published estimations of differences in the local cerebral blood flow (ICBF) between the RSEO and the RSEC shows that increase in the ICBF may be associated with a local decrease in the EEG spectral power in any frequency band, including the high-frequency β and γ bands, or several frequency bands simultaneously.     

Strategy and results: Sex differences in electrographic correlates of verbal and figural creativity

Sex differences in electroencephalographic (EEG) correlates of creativity were studied using verbal and figural divergent tasks to be performed in accordance with the instructions to “give any solution” or “give an original solution.” The common effect was a greater activity of the right hemisphere, which did not depend on the sex, task type, or instructions for performance of the tasks. The α₂ and β₂ rhythms were the main EEG frequency correlates of creative thinking; the degree and sign of their reactivity depended on the aforementioned factors. Although the creative abilities in men and women were similar under test conditions, the EEG correlates of both figural and verbal tasks were sex-dependent. A high reactivity of the α₂ rhythm was more marked during verbal creative thinking in women; and that of the β₂ rhythm, during figural creative thinking in men. The instruction-related improvement of the critical selection of solutions was to a greater extent reflected by changes in the cortical activity, more pronounced in the frontal cortex in the women. Thus, the same creative productivity in men and women was mediated by different strategies of performance of both figural and verbal tasks, and the sex-related differences in these strategies remained even when the motivation for creativity was changed.     

Effects of muscimol and flurazepam on the sleep EEG in the rat

In order to assess the possible role of GABA receptor function in the hypnotic property of benzodiazepines, we have examined the sleep EEG in rats given the GABA agonist muscimol, alone and in combination with flurazepam. Muscimol 0.05 and 0.1 mg/kg IP failed to alter sleep latency or total sleep time, and did not interact with the sleep-enhancing properties of flurazepam 20 mg/kg IP. These observations, in conjunction with a previous study of bicuculline, suggest that the hypnotic property of benzodiazepines may not be mediated by alteration of GABAergic activity.     

Characteristics of EEG reactivity changes during the performance of dual tasks in healthy subjects (voluntary postural control and calculation)

Comprehensive EEG and stabilography investigation with separate and simultaneous performance of motor (voluntary postural control) and cognitive (calculation) tasks has been performed in 20 healthy subjects (22 ± 0.7 years). Specific spatial and frequency reactive changes have been found during motor task performance. These included an increase in coherence in the EEG α band for distant derivation pairs in the right hemisphere, as well as in symmetric parietal-occipital areas in both hemispheres. Cognitive task performance was accompanied by an increase in coherence for the slow bands (δ and θ) with a higher activation in the left hemisphere and frontal cortex areas. In performing the dual task, one could observe activation of spatial and frequency changes including both motor and cognitive tasks. In the dual tasks where both components were performed worse as compared to the control, reactive reorganization of EEG coherence was less pronounced than during the performance of separate tasks. A decrease in the coherence of the α₁ band in the frontal areas appeared as a zone of “conflict of interest” or interference. In dual tasks with better performance of each component as compared to the control, EEG coherence increased in each specific area, as well as in the areas of “conflict of interests.”     

A digital signal processing system for EEG frequency analysis

This paper describes the digital signal processing work of a research project for studying children's cognitive processes by analyzing EEG signals during school-related tasks. The EEG being analyzed involves two homologous channels (left and right parietal area), and is recorded on magnetic tapes. The objective of the analysis is to determine if, by examining the alpha band of the ongoing EEG, different school tasks and correct vs incorrect responses can be detected. Analysis of alpha-band calls for the determination of signal power in the 7-12 Hz frequency band (adjusted for the age of the subjects) for each channel as well as correlation between the channels. A digital signal processing scheme implemented on an Apple II microcomputer was developed for such an analysis. The results obtained are discussed.     

Topographic Electrophysiological Signatures of fMRI Resting State Networks

Background

fMRI Resting State Networks (RSNs) have gained importance in the present fMRI literature. Although their functional role is unquestioned and their physiological origin is nowadays widely accepted, little is known about their relationship to neuronal activity. The combined recording of EEG and fMRI allows the temporal correlation between fluctuations of the RSNs and the dynamics of EEG spectral amplitudes. So far, only relationships between several EEG frequency bands and some RSNs could be demonstrated, but no study accounted for the spatial distribution of frequency domain EEG.

Methodology/Principal Findings

In the present study we report on the topographic association of EEG spectral fluctuations and RSN dynamics using EEG covariance mapping. All RSNs displayed significant covariance maps across a broad EEG frequency range. Cluster analysis of the found covariance maps revealed the common standard EEG frequency bands. We found significant differences between covariance maps of the different RSNs and these differences depended on the frequency band.

Conclusions/Significance

Our data supports the physiological and neuronal origin of the RSNs and substantiates the assumption that the standard EEG frequency bands and their topographies can be seen as electrophysiological signatures of underlying distributed neuronal networks.     

Does hypnotizability affect human upright stance?

Subjects highly (Highs) and low susceptible to hypnosis (Lows) show different imagery and attentional capabilities and also peculiar somatomotor, vegetative and electroencephalographic differences in basal and task conditions. Since attention is one of the main component of hypnotic susceptibility and also a relevant factor for postural control, the aim of the experiment was to study actual differences between Highs and Lows at the eyes closure during upright stance. Visual and motor imagery as well as attentional/disattentional capabilities were evaluated through psychological tests. Posture was monitored though Elite systems during upright stance with open and closed eyes. At the eyes closure, Highs and Lows exhibited a different body sway modulation. Possible different compensation mechanisms are suggested for the two groups and interactions between attentional/arousal systems responsible of hypnotic phenomenology and postural control are underlined.     

Changes in EEG coherence during tests for nonverbal (Figurative) creativity

Brain neurodynamics was studied by the EEG method during the performance of a task for figurative (or imaginative) creativity. The EEG was recorded in 19 standard derivations according to the international 10–20 system in 30 subjects. The following creative tasks were presented to subjects to involve them in the creative process: (Crl) thinking up and drawing an original picture; (Cr2) drawing a face, a house, and a clown in an original manner; (C1) drawing a picture from memory; and (C2) drawing geometric figures without any system. All the tasks had to be performed using a given set of geometric figures (a circle, semicircle, triangle, and rectangle). Statistical analysis of the EEG coherence function in these states for the frequency bands Δ, θ, α₁, α₂, β₁, β₂, and γ showed that the performance of creative and control tasks was associated with significant coherence changes in all the EEG frequency bands. As compared to the control tasks, performance of creative tasks caused an increase in the coherence of the α₁-and α₂ bands, more pronounced when creative tasks were compared with the second control task. In addition, the performance of the creative tasks (as compared to the control tasks) was accompanied by a decrease in the interhemispheric coherence of high-frequency rhythms (β₂ and γ) and an increase in the intrahemispheric coherence of these rhythms. The findings are compared to the results of previous EEG studies on creative activity.     

Comparison of the effects of the subjective complexity and verbal creativity on EEG spectral power parameters

The EEG recording was made when the subjects performed tasks that involved overcoming the stereotype (creative) and retrieving information from memory (noncreative) with the usual and complicated presentation of the initial material (incomplete proverbs and sayings without concluding words). The subjective complexity of the task performance under different conditions was assessed. The EEG power from 19 EEG derivations was compared in the β₂ and γ frequency bands. The creative task performance was associated with a marked increase in the EEG power; significantly more complicated noncreative tasks were not accompanied by marked changes in the EEG power in these bands.     

Sex differences in EEG power changes in retention of dichotically and monaurally presented verbal stimuli

EEG power mapping was used to study gender differences in hemispheric functional organization during memorizing dichotically and monaurally presented verbal information. Right-handed students (12 men and 14 women) participated in experiments. The EEG was recorded from 16 electrodes placed at homologous sites of the left and right brain hemispheres. Task-related changes in the thetal power in men differentiated between monaural presentations to different ears, i.e., situations of oppositely directed attention. In women the thetal power reactivity (the difference between the band power logarithms under baseline conditions and in task interval) differentiated between dichotic and monaural presentations of words, i.e., situations with different memory loads. Gender differences were also found in the alpha frequency band. Power changes in the alpha 1 band in all memory tasks and power changes in the alpha 2 were more evident in the right hemisphere in men but in the left hemisphere in women. In contrast, in the posterior temporal lead the alpha 2 power reactivity in men was higher in the right hemisphere, whereas in women the lateral differences were absent. As compared to men, the alpha 2 desynchronization in women was also more pronounced in posterior regions of both hemispheres. There were no gender differences in efficacy of memorizing. It is suggested that different processing strategies rather than different behavioral performance may be responsible for the revealed specific spatiotemporal EEG patterns.     

The effect of valproic acid on sleep structure and ethanol consumption in rats with various types of individual reactivity before and after stress exposure

The influence of valproic acid on sleep structure and alcohol motivation was studied in pretyped rats prior and following REM sleep deprivation. During EEG recording of wake-sleep cycle valporoic acid was shown to produce hypnotic action dependent on drug dosage in high active and low active animals. There was also shown that following REM sleep deprivation low active animals significantly reduced ethanol consumption under valproic acid influence. It seems likely from the results obtained that valproic acid could be used as hypnotic and antialcoholic drug.     

Automatic classification algorithms of the EEG monitor Narcotrend for routinely recorded EEG data from general anaesthesia: a validation study.

Impacts of hypnotic drugs on brain function are reflected in the EEG. The EEG monitor Narcotrend performs an automatic classification of the EEG using a scale which was proposed by Kugler for visual evaluation of the EEG. In this article the results of a validation study of the automatic classification algorithms implemented in the EEG monitor Narcotrend are presented. Visual and automatic classification of EEG data recorded in routine clinical practice were compared. The correlation between visual and automatic assessment was high (Spearman rank correlation r = 0.90, prediction probability Pk = 0.90) and a sufficient agreement between visual and automatic assessment was achieved for 92% of the analysed EEG epochs. The results of the study suggest that the automatic classification algorithms implemented in the EEG monitor Narcotrend yield a reliable assessment of the depth of hypnosis.