Individual dynamics of the EEG running wave under various conditions of activity

In 25 healthy subjects at resting with their eyes closed and open, a current phase structure of the EEG was measured, i.e. a trajectory and velocity of oscillation spreading over the head surface in temporal-occipital area. Visual computer multiplication revealed stable individual specifics of the EEG "running wave" dynamics which were then confirmed independently proceeding from the statistical significance criteria. Some subjects had characteristic transversal modulations of the EEG waves (from the left fo the right and vice versa), other subjects manifested longitudinal modulations along the diagonal from the cortex left anterior areas to the right posterior those (in some of them) or along the same diagonal in the opposite direction (in others). When opening the eyes, the character of the EEG "running wave" undergoes dramatic changes. Among other parameters, a growth of the trajectory share occurs in occipital area along with acceleration of the "running wave" spreading on all other trajectories. Both effects are bound to each other and the sharper dynamics is specific for subjects characterised as sympathotonic those as compared with para-sympathotonic.     

EEG markers of the stabilotraining effect during the rehabilitation of patients with posttraumatic Korsakoff’s syndrome

Nine patients with posttraumatic Korsakoff syndrome (KS) were examined before and after a rehabilitation course of feedback stability training (ST) using EEG, posturographic and clinical tests (with the FIM and Mayo Portland scales used for estimation). During 7 to 12 sessions, the patients tried to perform static and motor tasks. A group of 18 healthy subjects were examined to provide standard parameters. The results demonstrated a disturbed spatiotemporal EEG pattern in patients with KS before ST in the form of a reduced coherence for short derivation pairs (intrahemispheric, interhemispheric, and diagonal ones) in frontal and parietooccipital areas. Analysis of specific EEG rhythms demonstrated the maximum decrease in coherence in the α band (with the aforementioned regional specificity) and for long diagonal pairs (between the left frontal and right parietooccipital areas). The ST course was accompanied by KS regression (according to clinical scales and posturographic study); an original increase in EEG coherence, especially that of α waves, was recorded in the occipitoparietal and central frontal areas of the right hemisphere; a subsequent increase in coherence of the frontal areas in both hemispheres was observed. Late after the ST course, further positive changes were characteristic of the EEG spatiotemporal pattern. However, comparison with standard data suggested incomplete recovery of various coherence parameters: hypertrophied coherence in intrahemispheric pairs and still reduced values in interhemispheric derivations. This EEG pattern suggested incomplete KS regression, which was confirmed by clinical data.     

Correlation of EEG asymmetry and hypnotic susceptibility

Hypnosis research of the last decades confirmed that some cortical regions show characteristic modification of spontaneous brain electrical activity as a function of hypnotic responsiveness. Using FFT spectrum of 16 channel EEG recording, it was demonstrated that in highly susceptible subjects the right parieto-temporal region show more electric power than the left one while the low susceptibles have left side predominance or equilibrated power in all derivations. If a specific (Ericksonian) indirect hypnosis induction was administered, the same right side preponderance could be recorded in low susceptibles, too. On the basis of these results we can confirm the importance of the right parieto-temporal associative area in the alteration of consciousness characterizing hypnotic state.     

Reorganization of interhemispheric interactions during verbal-mental activity aimed at synthesis of words and sentences

Correlation and coherence analyses of multichannel electroencephalogram (EEG) recordings from 18 subjects (mean age 25 years) were used for investigating the reorganization of systemic interactions between bioelectric potentials of the cortical areas of both hemispheres (20 EEG derivations) during verbal-mental activity connected with generating verbal units from simpler components. When generating either words from aurally presented phonemes or sentences from a set of words, the subjects exhibited specific changes in the spatial structure of the statistical relationships in the EEG, with a significant increase in the interhemispheric interactions. During performance of both tasks, the changes in the interhemispheric interactions were most pronounced in the temporal, temporo-parieto-occipital (TPO), inferofrontal, and occipital areas of both hemispheres. Phonemic synthesis was associated with a more marked increase in the contralateral interactions in the left hemisphere, and generating sentences from words, in the right hemisphere. The coherence analysis of the EEG showed the greatest changes in the Δ, ?, and β frequency bands, with rather slight changes in the α frequency band. For all frequency bands, changes in the EEG coherences were the greatest in Wernicke’s and the TPO areas of the right and left hemispheres during the performance of both tasks, especially during the phonemic synthesis. These findings suggest that neurophysiological processes underlying mental generation of words and sentences require coordinated activity of the left and right hemispheres, which is accompanied by an increase in the interhemispheric interactions in the EEG, especially in the temporal, inferofrontal, and TPO areas.     

Spatial and temporal structure of phase synchronization of spontaneous alpha EEG activity

Spatiotemporal characteristics of spontaneous alpha EEG activity patterns are analyzed in terms of large-scale phase synchronization. During periods with strong phase synchronization over the entire scalp, phase patterns take either of two forms; one is a gradual phase shift between frontal and occipital regions and the other is a stepwise pattern with a sudden phase shift in the central region. The former is regarded as a traveling wave of electrocortical activity, of which the direction of propagation is predominantly from anterior to posterior in three out of four subjects, and opposite in the remaining one. The other activity pattern observed may correspond to a standing wave composed of two traveling waves propagating in opposite directions. The duration distributions of these patterns have similar forms within a subject, which suggests that they share the same mechanism for their generation.     

The influence of eye dominance on saccade characteristics and slow presaccadic potentials

Characteristics of saccades and presaccadic slow potentials were studied in 36 right-handed men with right (the RE group) and left (the LE group) eye dominance. Three light-emitting diodes located in the center of the visual field (the central fixation stimulus, CFS) and 10 deg to the left and to the right of the center (peripheral stimuli, PSs) were used for stimulation. The subjects performed a task with simple saccades to a PS and a task with antisaccades to the horizontal mirror position of the PS. Monopolar EEGs at 19 derivations and electrooculograms (EOGs) were recorded. Back averaging of the EEG time-locked to the PS onset or the saccade onset was used to obtain slow presaccadic potentials. The saccade characteristics in the RE and LE groups were similar. Differences between them were found only in the antisaccade task. The amplitude of negative presaccadic potentials (NPPs) time-locked to the PS in the frontal cortex was lower in the LE group compared to the RE group. Analysis of potentials time-locked to the saccade onset showed that changes in the slow potentials during the last 50 s before the saccade depended on the saccade direction and reflected the activation of the hemisphere opposite to the saccade direction. The activation of the right hemisphere before left-side saccades was higher in the LE than the RE group. In addition, the amplitude of NPPs was decreased in the frontal area and increased in the left posterior temporal area in the LE group compared to the RE group. The obtained results indicate that the involvement of the frontal cortex in cognitive and motor processes is decreased in subjects with the left eye dominance.     

Reduction of variability of EEG occipital,parietal, and central alpha rhythms by visual feedback stimulation

Two experiments, each with 24 normal right-handed adults, examined variability of the response of EEG alpha rhythms during repeated visual stimulations that were contingent on the occurrence of those rhythms. Within-trial variability of alpha durations and no-alpha (alpha blocking) durations were recorded from bipolar derivations along two bilateral posterior-anterior lines. Variability was significantly lower for: (1) the contingent EEG connected to the stimulus compared to the contralateral EEG, which was recorded simultaneously but was not connected to the stimulus; (2) occipitoparietal EEGs compared to parietocentral EEGs; (3) alpha durations compared to no-alpha durations. Differences in variability among the four EEG locations on the left or the right side were significant for contingent EEGs but not for contralateral nonconnected EEGs. The results were interpreted to be a demonstration that feedback EEG method can be applied to research on the functional topography of an EEG response to sensory stimuli in terms of the reduction of variability of the response that can be achieved with feedback.     

Functional asymmetry of the neocortex electrical activity during food conditioning in dogs

Four dogs were trained to perform a conditioned alimentary response to a sound stimulus. The EEG was recorded from six pairs of chronically implanted neocortical electrodes. The EEG spectra and coherence functions between the neighboring derivations of each of the hemispheres were analyzed in the theta, alpha, beta 1 and beta 2 frequency ranges. At the first stages of conditioning, the percent of cases increased when the highest mean values of EEG frequency were localized in the left hemisphere. Later on the percent of cases, when the mean coherence values in the left hemisphere were higher than in the right hemisphere, also increased. At the stage of conditioned response stabilization, this asymmetry either disappeared or the right hemisphere became more active than the left one. The spatial localization of the maximal values of the EEG frequency was different for different frequency ranges. The highest values in the beta 1 range were more frequently registered in the posterior cortical regions and in the beta 2 range they were revealed, predominantly, in the anterior areas. The maximal values of coherence dominated in the anterior regions and their spatial distribution was similar for different frequencies. Thus, the initial stages of conditioning are accompanied by activation of the left hemisphere.     

Electroencephalographic characteristic of cognitive-specific alerting attention in verbal learning--III: Localized characteristics of EEG spatial synchronization

Electroencephalograms (EEG) were recorder in 19 standard derivations in 88 healthy subjects, while they were in the states: rest with eyes open; memorization (learning) of verbal bilingual semantic pairs (Latin and Russian languages); the retrieval of the rote information from memory (control). We compared estimates of EEG coherence in these states for the frequency bands theta (4-7 Hz), alpha-1 (7-10 Hz), alpha-2 (10-13 Hz), beta-1 (13-18 Hz), beta-2 (18-30 Hz), gamma (30-40 Hz). When compared with the rest most strongly expressed: for memorization a decrease of coherence in the pairs of derivations from frontal and central areas of the cortex in the EEG frequency bands; for retrieval an increase of coherence in interhemispheric derivation pairs of pariental-occipital region in majority of the frequency bands. For the retrieval also increases of coherence in the beta2 and gamma bands, along with coherence decreases at low frequencies take place in pairs formed by derivations from the parieto-occipital region with derivations from the frontal and the central ones. Dynamics of EEG coherence in comparisons of memorization and retrieval from the rest and each are expressed significantly more in the interhemispheric and crosshemispheric pairs of derivations than in the intrahemispheric pairs. Revealed topographic specificity of the dynamics of EEG coherence by changing the states is considered in terms of ideas about cognitive-specific forms of sustained goal-directed mental attention.     

Tactile rivalry demonstrated with an ambiguous apparent-motion quartet

When observers view ambiguous visual stimuli, their perception will often alternate between the possible interpretations, a phenomenon termed perceptual rivalry [1]. To induce perceptual rivalry in the tactile domain, we developed a new tactile illusion, based on the visual apparent-motion quartet [2]. Pairs of 200 ms vibrotactile stimuli were applied to the finger pad at intervals separated by 300 ms. The location of each successive stimulus pair alternated between the opposing diagonal corners of the approximately 1 cm(2) stimulation array. This stimulation sequence led all participants to report switches between the perception of motion traveling either up and down or left and right across their fingertip. Adaptation to tactile stimulation biased toward one direction caused subsequent ambiguous stimulation to be experienced in the opposing direction. In contrast, when consecutive trials of ambiguous stimulation were presented, motion was generally perceived in the direction consistent with the motion reported in the previous trial. Voluntary eye movements induced shifts in the tactile perception toward a motion axis aligned along a world-centered coordinate frame. Because the tactile quartet results in switching perceptual states despite unvaried sensory input, it is ideally suited to future studies of the neural processes associated with conscious tactile perception.     

Long-range temporal correlations of broadband EEG oscillations for depressed subjects following different hemispheric cerebral infarction

Abnormal long-range temporal correlation (LRTC) in EEG oscillation has been observed in several brain pathologies and mental disorders. This study examined the relationship between the LRTC of broadband EEG oscillation and depression following cerebral infarction with different hemispheric lesions to provide a novel insight into such depressive disorders. Resting EEGs of 16 channels in 18 depressed (9 left and 9 right lesions) and 21 non-depressed (11 left and 10 right lesions) subjects following cerebral infarction and 19 healthy control subjects were analysed by means of detrended fluctuation analysis, a quantitative measurement of LRTC. The difference among groups and the correlation between the severity of depression and LRTC in EEG oscillation were investigated by statistical analysis. The results showed that LRTC of broadband EEG oscillations in depressive subjects was still preserved but attenuated in right hemispheric lesion subjects especially in left pre-frontal and right inferior frontal and posterior temporal regions. Moreover, an association between the severity of psychiatric symptoms and the attenuation of the LRTC was found in frontal, central and temporal regions for stroke subjects with right lesions. A high discriminating ability of the LRTC in the frontal and central regions to distinguish depressive from non-depressive subjects suggested potential feasibility for LRTC as an assessment indicator for depression following right hemispheric cerebral infarction. Different performance of temporal correlation in depressed subjects following the two hemispheric lesions implied complex association between depression and stroke lesion location.     

Hemispheric asymmetry of visual evoked potentials during human recognition of facial emotional expressions

Visual evoked potentials (VEP) in standard 16 EEG derivations were recorded in 26 young men and 20 women during recognition of facial emotional expressions and geometric figures. The stimuli were presented on a computer screen in the center of the visual field or randomly in the right or left vision hemifields. Peak VEP latency and mean amplitude in 50-ms epochs were measured; spatiotemporal VEP dynamics was analyzed in a series of topographic maps. The right hemisphere was shown to be more important in processing emotional faces. The character of the asymmetry was dynamic: at earlier stages of emotion processing the electrical activity was higher in the right inferior temporal region compared to the left symmetrical site. Later on the activity was higher in the right frontal and central areas. The dynamic mapping of "face-selective" component N180 of VEPs revealed the onset of activation over the right frontal areas that was followed by the fast activation of symmetrical left zones. Notably, this dynamics didn't correlate with the hemifield of stimuli exposition. The degree of asymmetry was lower during presentation of figures, especially in the inferior temporal and frontal regions. The prominent asymmetry of information processes in the inferior temporal and frontal areas was suggested to be specific for recognition of facial expression.     

EEG study of the functional organization of the right and left hemisphere during solution of verbal and spatial problems

In adult healthy right-handed subjects, the expression and degree of synchronization of the EEG alpha-range rhythmic components in different areas of the right and left hemispheres, were studied in a state of quiet wakefulness and during solving of verbal and spatial tasks presented in the visual field. The EEG of quiet wakefulness was characterized by different distribution of the alpha-range rhythmic components in the right and left hemispheres; in the right hemisphere low frequencies (7.5-10.5 c/s) were more expressed and more coherent; in the left one--the high frequencies (10.5-13.5 c/s). The solving of tasks was accompanied--along with a decrease of the whole alpha-range power spectra both in the right and the left hemispheres--by a local increase of synchronization of certain components of this range; the increase was specific to the hemisphere and the kind of task. The increase of synchronization of low-frequency components was observed in the right hemisphere during solving of the spatial task and that of the high-frequency components was noticed in the left hemisphere during solving of the verbal task. On the basis of the data on hemispheric specificity of electric activity synchronization of the alpha-rhythm, a suggestion is made about a different character of the functional integration of the structures of the right and left hemispheres in the process of solving of spatial and verbal tasks.     

Computational simulations establish a novel transducer array placement arrangement that extends delivery of therapeutic TTFields to the infratentorium of patients with brainstem gliomas

Background and PurposeTumor treating fields (TTFields) are a non-invasive, efficacious treatment modality currently approved for supratentorial glioblastomas. Despite their ability to improve overall survival in supratentorial tumors, the current placement of arrays is limited to the supratentorial head, precluding its use in infratentorial tumors. Infratentorial malignancies are in need of new therapy modalities given their poor prognoses in both children and adults. The aim of this research is to determine whether rearrangement of TTFields may allow for management of infratentorial tumors.Materials and methodsDelivery of TTFields using Novocure’s prototype Optune™ device human male head model was simulated based on brain MRIs from patients with brainstem gliomas to develop a novel array layout designed to extend adequate infratentorial coverage.ResultsArray placement on the vertex, bilateral posterolateral occiput, and superior-posterior neck achieved intensities above 1.1 V/cm (average 1.7 V/cm; maximum 2.3 V/cm) in the vertical field direction and above 1 V/cm (average 2 V/cm; maximum 2.8 V/cm) in the horizontal field direction of the infratentorium. The calculated field intensity within the simulated tumors were in the therapeutic range and demonstrated the effective delivery of TTFields to the infratentorial brain.ConclusionsOur findings suggest that rearrangement of the TTFields standard array with placement of electrodes on the vertex, bilateral posterolateral occiput, and superior-posterior neck allows for adequate electric field distribution in the infratentorium that is within the therapeutic range.     

The influence of support withdrawal on presaccadic EEG potentials in subjects with different asymmetry profiles

Characteristics of saccades and parameters of slow presaccadic potentials were studied in 12 volunteers, including seven subjects with a leading right eye (the RE group) and five subjects with a leading left eye (the LE group) before and on the sixth day of dry immersion. For visual stimulation, three light-emitting diodes were used; one of them was located in the center of the visual field, and two other, 10° away from the horizontal axis to the right and left of the first one. The subjects performed an anti-saccade test, which included making saccades at the spot that was symmetrically located in the visual field opposite to the stimulus. The EEG (19 standard unipolar derivations) and electrooculogram were recorded. To obtain slow presaccadic potentials (PSPs), backward averaging triggered by switching on a peripheral stimulus was performed. Before the immersion, there were no significant differences in the characteristics of saccades in both groups of subjects. At the same time, the amplitude of presaccadic negativity (PSN) in the LE group was decreased, especially in the frontal region, and had considerable asymmetry during the analysis. During the immersion, the latent periods of the saccades and the percentage of incorrect reactions did not change in RE subjects and were increased in LE subjects. Both groups demonstrated a decrease in the PSN amplitude and its shift to the right hemisphere; intergroup differences decreased in immersion conditions. The characteristic feature of the RE group was a significant decrease in PSN in frontal leas at immersion, apparently caused by sensory disintegration and a decrease in the tonic afferent input. In the LE group, the maximal amplitude of PSN was observed in the central region.     

Behavioral and electroencephalographic correlates of 40-Hz EEG biofeedback training in humans

Two groups of eight adults successfully trained with biofeedback for increases in 40-Hz EEG responses in left or right hemispheres also demonstrated significant 40-Hz EEG increases during baseline periods, and increases in the contralateral hemisphere during training periods. No changes in heart rate, 40-Hz EMG, or 21- to 31-Hz beta, alpha, or theta EEG occurred over training days. Three subjects returning for additional training demonstrated suppression of 40-Hz EEG. A group of four subjects experiencing daily bidirectional training produced substantial within-session control of 40-Hz EEG but no changes over days. Data from posttraining tests without feedback for successful subjects in both groups indicated significant control of 40-Hz EEG responses in the initial parts of these sessions, and some correlated changes in other EEG responses. Measures of successful subjects' experiences during training and control tests indicated awareness of changes in subjective concomitants of EEG responses. This study suggests further strategies for research on behavioral correlates of EEG activity.     

Self-regulation of hemispheric asymmetry

This study was performed to determine if individuals could demonstrate self-regulation of average EEG power of one hemisphere in comparison to the other. Temporal EEG was recorded from 8 males and 6 females. After a practice session, the subjects were instructed to increase or decrease the ratio of left to right temporal EEG. The subjects were given on-line feedback in the form of a graph presented via a computer display screen. The study demonstrated a significant ability of the subjects to change differentially the hemispheric power ratios upon instruction.     

Time-Dependent Statistical and Correlation Properties of Neural Signals during Handwriting

To elucidate the cortical control of handwriting, we examined time-dependent statistical and correlational properties of simultaneously recorded 64-channel electroencephalograms (EEGs) and electromyograms (EMGs) of intrinsic hand muscles. We introduced a statistical method, which offered advantages compared to conventional coherence methods. In contrast to coherence methods, which operate in the frequency domain, our method enabled us to study the functional association between different neural regions in the time domain. In our experiments, subjects performed about 400 stereotypical trials during which they wrote a single character. These trials provided time-dependent EMG and EEG data capturing different handwriting epochs. The set of trials was treated as a statistical ensemble, and time-dependent correlation functions between neural signals were computed by averaging over that ensemble. We found that trial-to-trial variability of both the EMGs and EEGs was well described by a log-normal distribution with time-dependent parameters, which was clearly distinguished from the normal (Gaussian) distribution. We found strong and long-lasting EMG/EMG correlations, whereas EEG/EEG correlations, which were also quite strong, were short-lived with a characteristic correlation durations on the order of 100 ms or less. Our computations of correlation functions were restricted to the spectral range (13–30 Hz) of EEG signals where we found the strongest effects related to handwriting. Although, all subjects involved in our experiments were right-hand writers, we observed a clear symmetry between left and right motor areas: inter-channel correlations were strong if both channels were located over the left or right hemispheres, and 2–3 times weaker if the EEG channels were located over different hemispheres. Although we observed synchronized changes in the mean energies of EEG and EMG signals, we found that EEG/EMG correlations were much weaker than EEG/EEG and EMG/EMG correlations. The absence of strong correlations between EMG and EEG signals indicates that (i) a large fraction of the EEG signal includes electrical activity unrelated to low-level motor variability; (ii) neural processing of cortically-derived signals by spinal circuitry may reduce the correlation between EEG and EMG signals.     

Gender differences in EEG coherent activity before and after training navigation skills in virtual environments

Gender differences in electroencephalographic activity (EEG) changes during navigation task performance after training were assessed in young adults. Female and male subjects were matched on initial navigation performance. EEG recordings were obtained while subjects navigated in an immersive virtual environment without visual cues, before and after a navigational skills training (9 sessions). In spite of task performance was similar in both groups, females showed higher theta band coherent activity between frontal and parietal and frontal and central regions than males before training. Correlation in theta band between fronto-central, fronto-parietal, and centro-parietal regions was enhanced in the left hemisphere for females but in the right hemisphere for males after training. Females also demonstrated a decreased in correlation in theta band over the right hemisphere between centro-parietal regions, whereas males demonstrated a similar effect over the left hemisphere. Navigation training seems to promote fronto-central-parietal synchronization in both genders but in different hemisphere. These results are interpreted as reflecting verbal-analytical working memory functions in females and global-spatial working memory mode in males.     

Ultradian rhythms in the EEG and task performance

The purpose of this work was to investigate the presence of ultradian rhythms in: 1. levels of electroencephalographic activation; 2. interhemispheric correlation and 3. the performance of two cognitive tasks, and the correlation between these variables. Eight volunteers, aged 20 to 30, participated in the experiment. Two sessions were carried out: one from 0800 to 1400 on one day and the other from 1400 to 2000 another day. Samples of EEG activity were taken every 15 min at rest with eyes open in left and right temporal, central, parietal and occipital derivations referred to the ipsilateral earlobe the performance on two tasks, one logico-analytical (left hemisphere functions) and one spatial test (right hemisphere functions) was assessed. As control, body and environmental temperature were recorded. To test for the presence of ultradian rhythms, the data were subjected to a Fourier analysis. Different EEG variables showed rhythmicity throughout the sessions, principally with slow oscillation periods (3 and 6h); ultradian rhythms with 3h periods were also found in body temperature, while task performance showed no significant rhythmic patterns during sessions. Finally, no significant correlations were found between physiological variables evaluated and task performance.