EEG correlates of individual differences in performance efficiency of students during examination stress

Performance of cognitive tests and EEG spectral power were evaluated in 39 students aged from 19-21 years in two conditions: during common educational process and immediately before examination (stress condition). Before examination, the performance was better in subjects with low level of spectral density in the delta band (in the occipital, parietal, central and frontal cortical areas) and high level of the alpha-rhythm spectral density in all the cortical areas, A decrease in performance scores before examination was correlated with an increase in the delta activity (in the right frontal and temporal cortical areas) and rise of the anxiety level (tested by Spielberger).     

EEG in mathematical logical problem solving

The model of mathematical logic tasks was developed at which decision there was a value coherence in delta-range raised. In low-frequency ranges (delta, theta, and alpha) a coherence of potentials of frontal cortex were increased. In high-frequency ranges (beta1, beta2, gamma) in frontal cortex coherence was decreased, and its increasing in central, parietal, temporal, and occipital areas with prevalence in the left hemisphere. Most changes of quantity of positive connections observed in value diagonal coherence. Analysis of spectral power EEG has shown, that at the decision of tasks there is a generalised raising on a cortex in delta-range. Theta-activity increased in a frontal cortex, and gamma band was raised in occipital areas. A spectral power in an alpha range mainly decreased.     

Spatial organization of biopotentials and decision-making time during purposeful mental activity in humans

Features of spatial organization of neocortical potentials were studied in subjects with different decision-making time during performing the task of memorizing and subsequently reproducing, on a monitor screen, a sequence of signals. The subjects with a short decision-making time differed from those with a long decision-making time in a higher level of the intra- and interhemispheric coherence in alpha EEG frequency band different neocortical areas during reproduction of a signal sequence (coherence in the frontal, central and parietal areas; coherence between the right central and the left frontal, central, parietal, occipital and temporal areas; coherence between the left occipital and both the frontal areas).     

Changes in electrical brain activity in patients with panic disorders

Brain electrical activity was recorded in 38 patients with typical and in 42 patients with atypical panic disorders, also in 30 normal controls. Compared to controls, patients both with typical and with atypical panic disorders differed significantly in reduced spectral power of the EEG alpha band in the right hemisphere. Moreover, in patients with typical panic disorders, the spectral power of the EEG beta1 band was increased in the frontal, temporal, central, and parietal areas of the right hemisphere. In patients with atypical panic disorders, the spectral power of the theta band was increased in the temporal areas of the right hemisphere. The changes in the EEG activity in patients with typical panic disorders are supposed to reflect an increase in activity of non-specific systems of the mesencephalic reticular formation, and the EEG changes in patients with atypical panic attacks may be associated with increased activity of the temporolimbic brain structures.     

EEG Correlates of Anxiety and Emotional Stability in Adult Healthy Subjects

We studied peculiarities of the spectral characteristics of EEG in 111 healthy adult subjects of both sexes. The levels of situative anxiety (anxiety state) and personal anxiety were estimated using the Spielberger–Khanin test system. To estimate anxiety-related properties of the personality, Cattel’s technique 16 PF (form А) was used. Estimates of situative anxiety demonstrated only two cases of positive correlation with the spectral power density (SPD) of EEG rhythms (SPDs of the beta2 rhythm in the right-hemisphere temporal and occipital regions; recording with the eyes open). Estimates of personal anxiety positively correlated with the SPDs of the beta1 and (especially) beta2 EEG rhythms. Under conditions with the eyes open, the number of significant correlations was greater, and correlations themselves were tighter than with the eyes closed. The closest correlations of the estimates of personal anxiety with the SPDs of the beta rhythm were found in frontal and central leads of both hemispheres and in parietal and occipital loci of the right hemisphere. Only a single case of correlation of the alpha rhythm SPD with personal anxiety (negative correlation, a parietal lead in the left hemisphere) was found. At the same time, rather numerous correlations of the alpha rhythm expression with an index congeneric to anxiety, the C factor by the Cattel’s questionnaire (emotional stability/instability), were found. Thus, the intense beta EEG rhythm can be considered an electrographic correlate of high situative and personal anxieties. At the same time, the alpha rhythm power correlates with the emotional stability of the individual. We suppose that persons with a well-developed alpha rhythm are characterized by active and stable functioning of the cerebral dopaminergic system; this simultaneously serves as a pre-requisite of high emotional stability and social adaptability.     

Physiological correlates of individual differences in decision-making time during purposeful mental activity in humans

EEG correlates of individual differences in decision-making time were studied in subjects performing the task of memorizing and subsequently reproducing, on a monitor screen, a sequence of signals. Forty-six students were volunteers in the study, carried out with the use of an original computer-aided technique. Pioneering data on the individual specificity of physiological processes underlying human mental activity were obtained. Individual differences in EEG characteristics related to differences in the temporal parameters of the decision-making stage were found. In a situation directly preceding the activity, subjects characterized by a short decision-making time exhibited higher powers of the Δ (in the occipital, parietal, and central cortical areas) and θ-(in both the central and the right frontal and temporal areas) EEG rhythms. The subjects with a short decision-making time differed from those with a long decision-making time in a higher power of the θ rhythm in the right temporal area during memorization and an increased θ rhythm power in the frontal areas during reproduction of a signal sequence.     

Changes in EEG rhythms during verbal and visual-image thinking

General and local characteristics of EEG activation were studied in frontal, central, temporal and occipital areas of the left and right cerebral hemispheres in 20 adult subjects during execution of various mental tasks. The analysis of the changes of five main EEG rhythms (delta, theta, alpha, beta-1 and beta-2) showed that EEG power decrease in alpha- and beta-frequency ranges is a reliable and sensitive index of brain activation at thinking. On this basis EEG activation mosaics are described at carrying out of each task and its systemic changes at transition from one type of task to another one, depending on their psychological structure--modality and complexity.     

Changes in the brain's electrical activity during habituation to verbal stimulus in subjects with high and low levels of personal anxiety

Brain electrical activity during habituation to repeated verbal stimulus was recorded in subjects with high and low levels of personal anxiety. During habituation of subjects with low anxiety, the spectral power of EEG alpha and theta bands increased in the frontal cortical areas. Such a reaction was not observed in subjects with high anxiety level. Moreover, during habituation traces, the latency of P300 of the auditory evoked potential increased. This parameter did not depend on anxiety level. The amplitude of P300 in the right temporal region was shown to be related to anxiety level: it increased after habituation in subjects with low anxiety and did not change in subjects with high anxiety.     

Use of spectral correlation method in a study of human emotional states

Application of a new approach to EEG analysis, i.e. of the method of spectral correlation, permitted identification of significant differences in spatial distribution of spectral power correlation for emotions of different quality, namely: anger and fear. It was shown that against the background of fear the topographic distribution of intracortical connections in the delta band was more extensive and included frontal, central, temporal, parietal and occipital regions. The emotion of anger evoked changes in the picture of spatial distribution of intracortical connections in the alpha band which resulted in appearance of a powerful focus of connections in the frontal regions. The greatest number of connections was found for the emotion of anger in the beta band--22 statistically significant correlations. Thus, a generalization of connections in the EEG high frequency bands is noted for the emotion of anger which is not characteristic of the emotion of fear.     

The influence of the respiratory cycle on the EEG

In order to evaluate the influence of the respiratory cycle on the EEG, we compared the power spectral analysis of the EEG performed by fast Fourier transformation during inspirium and exspirium in 10 healthy subjects. The measurement was performed during spontaneous breathing and then during eupnoe (0.25 Hz), bradypnoe (0.1 Hz) and tachypnoe (0.5 Hz) paced by a metronome. In the course of spontaneous breathing and bradypnoe, there was an increase in the delta power and in the total power in the anterior temporal region during inspirium in comparison with exspirium. The eupnoe was characterized by an inspiratory decrease in the delta power in the parietal region and in the total power in the frontal region. The tachypnoe resulted in a decrease of the beta power in the central region and a decrease of the theta power in the posterior temporal and in the occipital region during inspirium. In comparison of the EEG in eupnoe, bradypnoe and tachypnoe, a decrease of spectral power of all spectral bands was found except for delta during faster breathing frequencies and vice versa with a significant difference which was found mostly between bradypnoe and tachypnoe, less frequently between eupnoe and tachypnoe.     

Hemispheric organization of verbal memory functions in seasonal winter depression: electrophysiological analysis

Spatial organization of EEG power and coherence during memorization of dichotically presented lists of words were studied in patients with winter depression (N = 17) and control subjects (N = 22). In contrast to the control subjects, the depressed patients were characterized by the higher theta power in the right parietal and posterior temporal regions and the dominance of the alpha 2 in the left midfrontal area. The patients also differed in the lower theta 2 coherence in the left hemisphere and lower alpha 1 coherence in the right hemisphere. These effects showed different intrahemispheric distribution. The interhemispheric EEG coherence in the theta 2 range between the frontal areas and alpha 1 coherence between the left frontal and right posterior areas was lower in the patients than in the control subjects. Verbal-emotional interaction in depressions are discussed.     

Modifications of EEG Related to Repeated Static Grasp Efforts Developed by the Hand in Humans

The characteristics of EEG recorded before, in the course, and after three sequential static grasp efforts developed by the right hand were analyzed in 14 healthy volunteers of both sexes, 19 to 56 years old. The grasps were 3 min long, and intervals between the sequential trials were 5 min long. The mean intensity was, as a rule, the greatest in the first trial and decreased, because of fatigue, in the second and third trials. In the course of the grasp effort, significant (P ≤ 0.05) or close to significant decreases in the spectral power were observed in all trials within the alpha2 subrange in some frontal, central, and central/temporal leads. This reaction of desynchronization of alpha2 oscillations probably reflects activation of the sensorimotor cortical zones. Within the above period, the power of alpha2 oscillations increased in the occipital leads. In a few leads of the frontal group, the powers of delta, theta1, theta2, and alpha1 oscillations increased significantly (P < 0.05) in the course of the first trial. Such reaction was not observed in the second and third trials, while the powers of delta and alpha1 ranges increased in the occipital sites (P < 0.05). The powers of delta and theta oscillations increased, as compared with the control values, after the second and third grasps. Such specific EEG modifications in sequential trials can be related to the actions of a novelty factor in the first trial and a fatigue factor in the subsequent trials. The coherence coefficient (CC) of alpha and beta oscillations for symmetric leads usually increased in the course of the grasp. This effect reached a significance level (P < 0.05) for alpha2 oscillations in central, posterotemporal, parietal, and occipital pairs. The CC for beta2 oscillations increased in both temporal lead pairs. A drop in the interhemisphere coherence was more typical of the delta and theta1 ranges. Therefore, changes in the CC values show that the structure of interhemisphere interaction undergoes modifications with the development of the grasp static efforts. Neirofiziologiya/Neurophysiology, Vol. 37, No. 4, pp. 362–371, July–August, 2005.     

Correlation between the Activity of Dopaminergic Neurons of the Ventral Tegmentum and Spectral Power of the EEG Rhythms in Awake Cats

We studied correlations between the frequency of background impulse activity (BIA) of dopaminergic (DAergic) neurons of the ventral tegmentum (VT) and spectral power (SP) of the frequency components of EEG samples recorded in awake cats. The EEG was recorded monopolarly (electrodes were fixed in the cranial bones) from the frontal, occipital, and right and left temporal regions of the cortex. In a great majority of the cases, the BIA frequency of VT DA-ergic neurons demonstrated significant positive correlations with changes in the SPs of the alpha and beta EEG rhythms. The closest correlations of the spiking frequency of DA-ergic cells with the SP of the alpha rhythm was observed in the occipital region, while those with the beta SP were found in the frontal area. Correlations of the activity of DA-ergic neurons with the SPs of the alpha and beta rhythms in the left temporal cortical zone were closer, as compared with those in the symmetrical right zone. Correlations of the SPs of the delta, theta, and gamma EEG components with the discharge frequency of VT DA neurons were of opposite directions, and in most cases such correlations did not reach the level of significance. The results of this study show that, in some cases, specific EEG patterns can be considered indicators of the state of the cerebral VT DA-ergic system. Neirofiziologiya/Neurophysiology, Vol. 40, No. 4, pp. 359–367, July–August, 2008.     

Context-dependent EEG spectral characteristics during performance of tasks

Spatial and frequency EEG characteristics of two groups of healthy adult subjects were examined in two series of experiments, which differed in conditions of the second cognitive task in a trial. The first task was the same in the two series: subjects had to evaluate size relationship between two closely spaced circles. The second task successively presented in trials of the first series consisted in the recognition of words/pseudowords, and in the second series, subjects had to localize a target letter in a matrix. It was assumed that the cognitive performance in the first series predominantly involved the ventral visual system, whereas during task performance in the second series, predominant involvement of the ventral and dorsal visual systems alternated. Multichannel EEG fragments recorded prior to the presentation of the task pairs were analyzed. Analysis of variance of the EEG spectral power revealed the generalized significant effect of the factor of the second task in the pair for delta band and lower beta subband, the power being higher in the first series. Factor brain hemisphere had a significant effect for the alpha band in the occipital area, the spectral power being lower in the left hemisphere for both experimental series. The task x hemisphere interaction was significant in the temporal cortical areas for the EEG power in alpha2 band, i.e., the predominant involvement of the ventral visual system was associated with stronger asymmetry of alpha2 rhythm and lower spectral power in this band in the left temporal area. Thus, the character of the forthcoming cognitive activity was shown to be reflected in spatio-frequency characteristics of the preceding EEG.     

Psychophysiologic parameters of reproducing emotions in healthy subjects and patients during the first episode of depression

We analyzed the spectral power of EEG rhythms and some psychological features in patients with depression (first episode) and in healthy subjects. In the control group, the distributions of the spectral power of the alpha3 and gamma rhythms was symmetrical. In reproducing joy, the power of the alpha3 rhythm increased in the occipital and that of the gamma rhythm increased in the temporal areas of the left hemisphere. In depressive patients, predominant activation of the left posterior cortical quadrant in the alpha3 band was observed both in the baseline activity and during reproducing emotions of both valences. In these patients, the gamma rhythm predominated in the anterior regions of the right hemisphere during rest. The mental reproduction of joy and grief in depressive patients shifted the maximal gamma rhythm spectral power to the occipital cortical regions. Thus, in depressive patients, any emotional load, regardless of its valence, results in a decrease in the pathologic gamma activity and makes the distribution of cortical electric activity more close to that of healthy subjects.     

Brain Networks Responsible for Sense of Agency: An EEG Study

BackgroundSelf-agency (SA) is a person’s feeling that his action was generated by himself. The neural substrates of SA have been investigated in many neuroimaging studies, but the functional connectivity of identified regions has rarely been investigated. The goal of this study is to investigate the neural network related to SA.MethodsSA of hand movements was modulated with virtual reality. We examined the cortical network relating to SA modulation with electroencephalography (EEG) power spectrum and phase coherence of alpha, beta, and gamma frequency bands in 16 right-handed, healthy volunteers.ResultsIn the alpha band, significant relative power changes and phase coherence of alpha band were associated with SA modulation. The relative power decrease over the central, bilateral parietal, and right temporal regions (C4, Pz, P3, P4, T6) became larger as participants more effectively controlled the virtual hand movements. The phase coherence of the alpha band within frontal areas (F7-FP2, F7-Fz) was directly related to changes in SA. The functional connectivity was lower as the participants felt that they could control their virtual hand. In the other frequency bands, significant phase coherences were observed in the frontal (or central) to parietal, temporal, and occipital regions during SA modulation (Fz-O1, F3-O1, Cz-O1, C3-T4L in beta band; FP1-T6, FP1-O2, F7-T4L, F8-Cz in gamma band).ConclusionsOur study suggests that alpha band activity may be the main neural oscillation of SA, which suggests that the neural network within the anterior frontal area may be important in the generation of SA.     

Brain bioelectrical activity at a high anxiety level in humans

Brain bioelectrical activity was studied in 38 and 34 subjects with high and low levels of anxiety, respectively, by means of toposelective mapping of EEG spectral power and recording of P300 endogenous event-related auditory evoked potentials (EPs). Analysis of EEG spectra demonstrated, in the subjects with a high level of trait anxiety, a higher power of β₁ oscillations in the central-parietal areas of both hemispheres and the occipital area of the right hemisphere, as well as a higher power of θ and α oscillations in the frontal areas of both hemispheres and the central-parietal area of the left hemisphere. The occipital-frontal gradient of the spectral power of these rhythmic EEG components was altered in subjects with a high level of trait anxiety. Comparison of P300 cognitive auditory EPs in the subjects with high anxiety and in the control group showed that, in the former, the P300 EP amplitude and the habituation distortion (dishabituation) of the P300 EP amplitude were significantly higher in both hemispheres. This indicates that, at a high level of anxiety, the active directed attention was disturbed, which is confirmed by the results of neuropsychological examination, demonstrating reduced selectivity, concentration, and stability of attention in the Münsterberg test and Schulte’s test. The results of electrophysiological examination suggest that the malfunction of regulatory brain modulating systems is an important neurophysiological mechanism of attention pathology and disturbed adaptation in subjects with a high level of trait anxiety.     

Neural Activations during Visual Sequence Learning Leave a Trace in Post-Training Spontaneous EEG

Recent EEG studies have shown that implicit learning involving specific cortical circuits results in an enduring local trace manifested as local changes in spectral power. Here we used a well characterized visual sequence learning task and high density-(hd-)EEG recording to determine whether also declarative learning leaves a post-task, local change in the resting state oscillatory activity in the areas involved in the learning process. Thus, we recorded hd-EEG in normal subjects before, during and after the acquisition of the order of a fixed spatial target sequence (VSEQ) and during the presentation of targets in random order (VRAN). We first determined the temporal evolution of spectral changes during VSEQ and compared it to VRAN. We found significant differences in the alpha and theta bands in three main scalp regions, a right occipito-parietal (ROP), an anterior-frontal (AFr), and a right frontal (RFr) area. The changes in frontal theta power during VSEQ were positively correlated with the learning rate. Further, post-learning EEG recordings during resting state revealed a significant increase in alpha power in ROP relative to a pre-learning baseline. We conclude that declarative learning is associated with alpha and theta changes in frontal and posterior regions that occur during the task, and with an increase of alpha power in the occipito-parietal region after the task. These post-task changes may represent a trace of learning and a hallmark of use-dependent plasticity.     

Classification of the adolescent EEG by the spectral and segmental characteristics for normals

The 16-channel EEG records of 45 adolescents with schizophrenia and 39 healthy adolescents were subjected to statistical combinatorial analysis of 160 elementary EEG characteristics (6 spectral and 4 segmental EEG characteristics for a channel). Employing pattern recognition algorithm "Kora-n", a list of 37 combined EEG patterns was compiled. This list characterized with a minimal error the EEG of healthy adolescents in such a way that none of these characters featured the EEG of adolescents with schizophrenia. Analysis of this list of EEG characteristics suggests that the contrast between EEG of healthy and ill adolescents is the sharpest in the F4, Cz, T3 and O1 derivations. Compared to EEG samples of schizophrenic subjects, EEGs of healthy subjects exhibit lower levels of delta and theta activity mainly in the frontal and temporal regions of the cortex and higher level of alpha activity predominantly in the occipital region. Applicability of the list of EEG patterns for diagnostics of schizophrenia-type disorders of adolescents is discussed.     

Influence of informational oversaturation on the quality of creative activity and spatial organization of EEG

The features of the spatial organization of bioelectric potentials in the cases of successful and unsuccessful creative imagination (refusal or poor quality of the product) under conditions of informational oversaturation. Two groups of subjects were compared: professionals (23 healthy students of the Department of Graphic Arts) and non-professionals (34 persons whose specialties were not linked with systematic visual imagination). During the experiments, the subjects were asked to mentally create a visual image based on two simple graphic elements, a right angle and a diagonal; after recording the EEG, they had to draw the image on paper and give it a title. The total number of elements exceeded 7 ± 2; hence, information processing at the conscious level was impossible, which caused the necessity of involving the mechanisms of unconscious information processing. The quality of the created product was evaluated with regard to the degree of success of performing the task and the features of spatial EEG organization. The EEG was recorded from 24 scalp sites of a subject using a SIT-EEG portable telemetric device. In the case of the successful performance of the task by professionals, the parameters of spatial organization of bioelectric potentials, i.e., spatial synchronization (linear processes) and spatial disorder (non-linear process) were strengthened compared to the base-line level in the frontal temporal areas of the right hemisphere and parietal occipital areas of the left hemisphere. Conversely, in the nonprofessionals, these parameters increased in the frontal temporal areas of the left hemisphere and parietal occipital areas of the right hemisphere. In the case a task was not successfully performed by the professionals, the spatial disorder of bioelectric potentials increased in all the cortical areas; in the nonprofessionals, only weak changes were observed. In all situations, the groups differed also in the parameters of coherence (Coh), spectral power (Sp) of bioelectric potentials, and informational energy, which reflects the level of expenditure of the brain’s energy for information processing. The evidence obtained is interpreted in terms of electroencephalographic correlates of successful task performance by professionals and nonprofessionals, i.e., their creative imagination under the conditions of informational over-saturation.