EEG spatial organization during intense hyperventilation (cyclic breathing): II. EEG correlates of psychovisceral phenomena

EEG correlates of two main effects of long-term hyperventilation (cyclic breathing similar to rebirthing), namely, psychotic manifestations and sensations in internal organs, are considered. Standard EEGs of 44 subjects were recorded and subsequently treated by multiparametric methods. It was shown that, in the case of psychotic phenomena (hallucinations, visual and auditory images, different scenes, virtual travels, out-of-body experiences, etc.), the changes in the spatial organization of bioelectric potentials as compared with the baseline have different patterns than in the case of sensations in internal organs. The changes are observed in the frontal regions of the cortex: a decrease in spatial synchronization (linear processes) during an increase in spatial disarray (nonlinear processes) of bioelectric potentials and the intensifying of high-frequency β activity. If sensations in internal organs appear, a decrease in the above parameters was observed in the right hemisphere and in posterior cortical areas. The data are discussed from the viewpoint of qualitative specificity of changes in functional states during an altered state of consciousness with manifestations of different psychovisceral phenomena.     

Participation of lactic anaerobic metabolism during short and intense repeated exercises

The evolution of blood lactate concentrations has been studied during a force/velocity test on a cycloergometer in order to specify if the repetition of short (6 s) and intense exercises induced an important participation of lactic anaerobic metabolism. Seven moderately trained male subjects, aged from 23 to 29 years (mean = 24.92 +/- 0.79) participated in this study. Two blood samples (venous catheter) were performed, at rest, then for each work load (1 kg to 10 kg): at the end of the exercise (P1) and during the recovery at 5 min (P2). From the lowest work load, blood lactate concentration increased significantly, at the end of the exercise (F = 16.21; P less than 0.001) and during the recovery (F = 22.62; P less than 0.001). The mean values were respectively at the peak of power: 9.84 +/- 0.85 et 10.19 +/- 0.75 mmol.l-1. Once the peak of power was obtained, the blood lactate concentration remained steady. In conclusion, the repetition of short and intense exercises induced an important participation of lactic anaerobic metabolism. The lactate could be the limiting factor of the maximal power.     

The EEG spatial pattern and psychophysiological characteristics of divergent and convergent thinking in humans

The psychophysiological parameters of the spatial synchronization of bioelectric potentials during the nonverbal divergent, nonverbal convergent, verbal divergent and verbal convergent thinking have been analyzed. The relationships between the performances of tests for these thinking styles were different. The strongest significant correlation has been found between the productivities of the verbal divergent and verbal convergent thinking styles; the weakest correlation, between those of the nonverbal divergent and nonverbal convergent thinking styles. The thinking styles differ from one another in the topography of spatial synchronization of bioelectric potentials. They are the most pronounced during the two nonverbal tasks and the least pronounced during the two verbal tasks. The thinking styles also differ from one another in the degree of the enhancement of the coherence between bioelectric potentials during tasks compared to the baseline (with the eyes open). Some human psychophysiological characteristics facilitating the performance of divergent (creative) tasks have a negative effect on the performance of convergent (noncreative) tasks. The data are discussed in terms of the differences in the level of general activation and involvement of different types of information processing (simultaneous and successive).     

Parameters of the spatial of organization of EEG in persons with various individual characteristics

The relationships between some characteristics of EEG topographic maps and personality traits (extraversion-introversion, sensation-intuition, thinking-feeling, judging-impulsiveness) by the Keirsey's Type Inventory were studied in 46 17-20-year-old men). The most considerable distinctions in the spatial organization of the EEG were observed between the functions sensation and intuition. The high-sensation responders were characterized by higher EEG power in the theta 1, 2 and alpha 1-bands in all derivations and higher coherence (especially in the theta 1, 2 bands most expressed in the frontoparietal areas) as compared with the high-intuition responders. The expression of extraversion was positively correlated with coherence values in the theta 1, 2 and negatively correlated with coherence in the alpha 1, 2 bands. Characteristic EEG patterns for other types of personality traits were also described. The results suggest that some characteristics of brain maps reflect the individual psychological features determined on the basis of Jung's typology.     

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

Electroencephalograms (EEGs) were recorded in 19 standard derivations in 88 healthy subjects (students) in the state of rest with eyes open and during memorization (learning) of verbal bilingual semantic pairs (the Latin and Russian languages) and retrieval of information from memory (control). The estimates of EEG coherence in these states were compared for the following frequency bands: θ (4–7 Hz), α₁ (7–10 Hz), α₂ (10–13 Hz), β₁ (13–18 Hz), β₂ (18–30 Hz), and γ (30–40 Hz). Compared to the state of rest, the decrease in coherence in the pairs of derivations from the frontal and central cortical areas in all EEG frequency bands was the most pronounced for memorization, and the increase in coherence in the interhemispheric derivation pairs of the parietal-occipital region in most of the frequency bands was the most pronounced for retrieval. In addition, in the pairs formed by derivations from the parietal-occipital region with derivations from the frontal and central regions, retrieval is also characterized by an increase in coherence in the β₂ and γ bands along with its decrease in the low-frequency ranges. The dynamics of EEG coherence, when comparing the states of memorization and retrieval, is more statistically significant in the interhemispheric and cross-hemispheric pairs of derivations than in the intrahemispheric pairs. The revealed topographic specificity of the dynamics of EEG coherence owing to the change of state is considered in terms of the notion on cognitive-specific forms of sustained goal-directed mental attention.     

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.     

EEG patterns suggestive of shifted levels of excitation effected by hathayogic exercises

Concurrent with the performance of hathayogic exercises such as Nauli, Bhastrika and Suryabhedana, three characteristic EEG patterns were identified: a "wicket" rhythm at a frequency wave of 12 to 17 Hz, recordable from para-Rolandic areas, which we have called Xi rhythm; a 26-33 Hz sinusoidal activity, confined to the mid-sagittal parietooccipital region; and paroxysmal activity localized in the lateral boundaries of parieto-temporo-occipital regions, bilaterally. - The expectation that hathayogic exercises would affect the electrical activity of circumscribed, relatively well defined areas of the brain was based on the fact that these exercises imply a strong stimulation of somatic and splanchnic receptors, the afferent impulses of which are fed into specific cortical representation areas localized for the most part around central and anterior parietal areas.     

EEG spatial organization and activation of creative processes

Characteristic features of the spatino-temporal EEG organization of 24 right-handed children (aged from 8 to 13 years) were studied after stimulation of creative activity by the method of self-regulation of the brain functional state (Russian Inventor's Certificate no. 2157707, 01.06.1999). The multiparametric analysis of baseline recordings derived from 24 cortical points made it possible to find the most probable pattern of changes in the spatial synchronization of biopotentials, including increase in activity in the right anterior and left posterior cortical regions. These changes were accompanied by a rise in the information-energy parameter (the ratio between coherence and spectral power of potentials). This phenomenon may testify to a transition to the "economic" condition of information processing. Differences in EEG frequency characteristics corresponding to different levels of imagination and creative intuition were revealed.     

Local discriminative spatial patterns for movement-related potentials-based EEG classification

A novel discriminant method, termed local discriminative spatial patterns (LDSP), is proposed for movement-related potentials (MRPs)-based single-trial electroencephalogram (EEG) classification. Different from conventional discriminative spatial patterns (DSP), LDSP explicitly considers local structure of EEG trials in the construction of scatter matrices in the Fisher-like criterion. The underlying manifold structure of two-dimensional spatio-temporal EEG signals contains more discriminative information. LDSP is an extension to DSP in the sense that DSP can be formulated as a special case of LDSP. By constructing an adjacency matrix, LDSP is calculated as a generalized eigenvalue problem, and so is computationally straightforward. Experiments on MRPs-based single-trial EEG classification show the effectiveness of the proposed LDSP method.     

Spectral-spatial characteristics of theta range in the EEG of students with various productivity of performance for visual spatial tasks

Examinees, which consisted of 46 young males, were offered to memorize and recreate a sequence of signals on a computer monitor. These signals were to be recreated in regard to the original sequence and location. Examinees were divided into two groups depending on their degree of approximation of the correct location of the signal sequence. The first group, unlike the second (in contrast to the second one), had a very high rate of accuracy with the least number of mistakes. EEG reading was taken on the examinees prior to completing the test, during the memorization stage and during the completion of task. The EEG reading taken prior to the test and those of the completion of task showed no difference in the range ofteta rhythm for both groups of examinees. However, during the memorization stage, the examinees of the first group, unlike that of the second, showed an increase in the coefficient of proximity in the line of teta rhythm EEG of the right hemisphere of the brain. Three systems of connection with the focuses of activity in the right rear, right center and right front areas of the brain, in which the proximity of teta range of EEG during the memorization stage, were noticeably higher in the group of examines that showed high accuracy during the primary attempts of recreation of the sequence. Since the right hemisphere deals mainly with spatial perception of the information and is more active at processing of nonverbal and stereotyped signals, we suggest that students belonging to different groups employed different strategies of processing of the task during remembering.     

Human mediotemporal EEG characteristics during propofol anesthesia

Evidence for a response-control-related kind of declarative memory during deep propofol anesthesia has recently been reported. Connectivity within the mediotemporal lobe (MTL), and in particular rhinal–hippocampal synchronization within the gamma band, has been shown to be crucial for declarative memory formation. Thus, we analyzed EEG recordings obtained from the scalp, as well as directly from within the hippocampus and from the anterior parahippocampal gyrus, which is covered by rhinal cortex, in patients with unilateral temporal lobe epilepsy during propofol anesthesia, which preceded electrode explantation. For the gamma band a power decrease starting with induction of anesthesia was observed at scalp position Cz, but a power increase was detected at MTL locations. In contrast to prior results for sleep recordings, rhinal–hippocampal coherence did not decrease within the gamma band at deeper levels of anesthesia. These findings may represent an indirect electrophysiological correlate of partially intact declarative memory formation during deep propofol sedation. Furthermore, we investigated how well the plasma propofol level, as well as different stages of anesthesia including the burst suppression phase, could be monitored by different spectral as well as by nonlinear EEG measures. We observed that conventional spectral power measures, most prominently those recorded from mediotemporal locations, are most closely correlated with the plasma propofol level, whereas different stages of anesthesia can be distinguished best by nonconventional spectral as well as nonlinear measures.     

The influence of visual imagery experience on EEG spatial organization

The comparison of EEG spatial organization between groups of 23 students of graphic arts department ("professional" subjects) and 39 subjects of another specialization ("non-professional" subjects) was made in order to find EEG correlates of visual imagery experience. Changes in the spatial organization of biopotentials (spatial synchronization and spatial disorder, spectral power and coherence) were analyzed while subjects mentally composed visual images from two simple elements, right angle and oblique line. The total number of elements presented for the image composition increased with each subsequent task (in total, four tasks were presented) from the number adequate to simultaneous perception and conscious processing (less than 7 +/- 2) to a much higher number. Intergroup differences, especially, in the degree of the spatial disorder (non-linear processes), were most evident under conditions when the subjects operated with a greater number of elements (tasks 3 and 4). This parameter increased more rapidly in "professionals" than in "non-professionals". These changes were most pronounced in the right anterior cortex. In "non-professional" subjects, spatial synchronization (linear processes) increased in the right posterior area. In "professional" subjects, coherence and spectral power increased in a greater number of narrow EEG frequency subbands than in "non-professional" subjects. The findings suggest that the imagery performance in subjects with visual imagery experience involves complicated neurodynamic processes such as non-linear dynamics and numerous EEG spatial resonance systems.     

Regularized common spatial patterns with subject-to-subject transfer of EEG signals

In the context of brain-computer interface (BCI) system, the common spatial patterns (CSP) method has been used to extract discriminative spatial filters for the classification of electroencephalogram (EEG) signals. However, the classification performance of CSP typically deteriorates when a few training samples are collected from a new BCI user. In this paper, we propose an approach that maintains or improves the recognition accuracy of the system with only a small size of training data set. The proposed approach is formulated by regularizing the classical CSP technique with the strategy of transfer learning. Specifically, we incorporate into the CSP analysis inter-subject information involving the same task, by minimizing the difference between the inter-subject features. Experimental results on two data sets from BCI competitions show that the proposed approach greatly improves the classification performance over that of the conventional CSP method; the transformed variant proved to be successful in almost every case, based on a small number of available training samples.     

Features of spatial organization of EEG and psychophysiological characteristics of the person with the divergent and convergent types of thinking

The psychophysiological indicators of spatial synchronization of biopotential at different types of mental processes in humans: non verbal-divergent, nonverbal-convergent, verbal-divergent and verbal-convergent were analyzed. The unequal relationship between the productivity of the implementation of tests on these types of thinking was revealed. The closest significant correlation exists between the productivity of the verbal-divergent and verbal-convergent thinking, and the lowest--between the productivity of nonverbally-divergent and nonverbally-convergent thinking. The differences in the topographical maps of the spatial synchronization of biopotential at different types of thinking was marked. They are most pronounced in the implementation of two non-verbal tasks, minimal--in two verbal tasks. Differences between different types of thinking are also manifested in the degree of coherence gain biopotential of the performance tests in comparison with the background (open eyes). Some physiological properties of the person that contribute to the divergent (creative) tests have a negative impact on the implementation of converged (tedious) tests. The findings are discussed in terms of differences in the level of general activation and participation of different ways of processing information (simultaneous and successiveness).     

Transformation of kinematic characteristics of a precise movement after change in a spatial task

Brain mechanisms of motor programming were studied with the use of the model of learning precise horizontal elbow flexion. To exclude visual control and make learning to be based, predominantly, on proprioception, experiments were carried out in darkness. The target position was not demonstrated beforehand. Subject (S) had to find an adequate angle of flexion during training with a short light-diode flash which marked the moment of target reaching. Ss were asked to perform a precise horizontal elbow flexion as fast as possible. Movement amplitude, velocity and acceleration were on-line recorded. Ten Ss were divided in two groups. The first group was initially trained to make the precise movement with the preset amplitude of 70 degrees and the second group had to perform similar movement with the amplitude of 55 degrees. Each S was trained to the moment of acquisition of a stable skill (within the 5% error of preset flexion amplitude). After that the target position was unex pectedly changed (from 70 for 55 degree or visa verse). This work was a continuation of our earlier search for a mathematical hypothesis most correctly explaining the central mechanism of motor learning. The dynamics of kinematic characteristics of learning in our experiments fitted well to A. Barto and J. Houk's "Cerebellar Model of Timing and Prediction". A comparison of a computer simulation of this model to the learning characteristics allowed us to make some refinements of the model very important for data analysis possible under conditions of noninvasive investigations. The analysis of acceleration dynamics not considered by the authors of the model made it possible to identify this index with the "pulse phase" similar to the period of LTD of Purkinje cells (the key mechanism of the model). We took such an interpretation as principal in our analysis of experimental data. We analyzed integrals of positive and negative acceleration which made it possible to gain a deeper insight into the physiological mechanism of a replacement of one central command by the other as a consequence of change in spatial task conditions.