Spectral EEG characteristics in students with different anxiety profile during tests

EEG spectral power was calculated in 39 students at the age of 19-21 years in two experimental conditions: during the common educational process and immediately before an examination (stress condition). During the education process, in subjects with high anxiety (tested by Spielberger) the relative spectral power of the delta activity was higher than in the other group in the occipital, parietal, central, and right frontal brain areas, whereas the power of the EEG alpha in these areas was lower. Before examination tests, in subjects with high activity the delta power bilaterally increased in the temporal areas, whereas in subjects with low anxiety there was a decrease in the alpha rhythm power, especially in the right frontal area. In stress condition, the relative power of the delta activity in both occipital and temporal, right parietal and central areas was higher in subjects with low anxiety, whereas their alpha power was lower in both frontal and in occipital, parietal, and temporal areas of the left hemisphere.     

Individual resistance to factors of monotony reflected in the EEG

Three groups of operators substantially different in their performance quality were examined. Under conditions of monotonous activity, subjects with the highest initial level of activation, minimum EEG total spectral power, and minimum level of EEG coherence in the frontal cortical areas worked most steadily. Under the same conditions, subjects with a rather high spectral power of the theta and beta2 EEG frequency components, highest coherence in the frontal areas, and low coherence in the caudal areas of the cortex worked least steadily. EEG phenomena testify to a rather low level of activation of the frontal cortical areas associated with a facilitation of cortico-subcortical neuronal interactions and an attenuation of the operating neural streams. This results in a decrease in the level of any attention, its involuntary switching, and short-term loss of the control over the current performance.     

Comparative study of the gamma-rhythm in the norm, pre-examination stress and patients with the first depressive episode

The work gives the results of comparative analysis of gamma-rhythm (30-40 Hz) spectral power and synchronization indices in the healthy subjects both in normal situation and before the examination with that of depressive patients with the first episode, in the rest condition and during cognitive tests performance. It is demonstrated that gamma-rhythm spectral power in frontal and temporal areas of depressive patients was significantly higher than that in the norm. In stressful situation the number of differences of healthy subjects from depressive patients decreased in the rest condition and in Kraepelin test. Spatial imagination revealed more significant differences between depressive patients and healthy subjects both in normal and in stressful situations. Gamma-rhythm synchronization level was the same in healthy subjects both in the rest condition and during the tests performance, but in stressful situation it increased in the latter situation as well as in depressive patients. Thus, in the most cases stressful situation decreases the differences of EEG indices between healthy subjects and depressive patients both in the rest condition (by spectral power) and during the tests performance (by both indices). This may point out stress as the "trigger" of depression.     

Development of examination stress in subjects with various levels of cortical activation

The work is aimed at the study of neurophysiological mechanisms of examination stress in subjects with different levels of cortical activation. Spectral power and typical cortical connections of EEG rhythms were studied in students under conditions of stress before and immediately after examination as well as during usual academic semester. Students with relatively higher and relatively lower baseline alpha rhythm, i.e., with different levels of cortical activation revealed both similar and different EEG reactions. Before examination, in both groups of subjects the spectral power of EEG activity in the delta and thetal bands increased, and the number of connections in the bands of the alpha and beta 1 rhythms decreased as compared to usual baseline conditions. However, the EEG reactions in the theta 2 band in the two groups were oppositely directed. Significant changes in the beta 2 power were observed only in the group of subjects with higher baseline level of cortical activation.     

The cortical interactions in short time intervals during the search for verbal associations

Cortical connectivity was studied in tasks of generating the use of words in comparison with reading aloud the same words. These tasks were used earlier in PET and high-density ERP recording studies, which described both the functional anatomy and time course of involvement of cortical areas in word processing. We developed a new method for studying the synchrony of EEG spectral components within the short time intervals compatible with the duration of particular cognitive operations. The wavelet transform of the ERP records and calculation of correlations between the wavelet curves were used to reveal connections between cortical areas. Three stages of intracortical communications developing over the course of task performance were discovered: between the right and left frontal areas (0-200 ms after the stimulus presentation), between the left frontal and left posterior temporo-parietal areas (250-500 ms), and, finally, between the left temporal and right fronto-centro-temporal areas. These findings are in good agreement with the results of the previous PET and ERP studies and supplement them with the circuitry of cortical information transfer. Also, they suggest some differences in information processing during automated reading and performance of more complicated use-generation task.     

Electrophysiological correlates activated during the Wisconsin Card Sorting Test (WCST)

In the present study we investigated changes in Event-Related Potentials (ERPs) during the Wisconsin Card Sorting Test (WCST) in order to identify cognitive processes underlying the set-shifting aspects of the task and to determine test sensitivity for frontal and prefrontal cortical areas. ERP's were recorded from a sample of 20 healthy adults while they performed a computerized version of the Grant & Berg (1948) version of the WCST, using 32-channel electroencephalogram recordings. The ERP waveforms were calculated for the set-shifting trials, or more precisely for the 2nd and the 3rd trials in the WCST series (set change condition) and compared to those associated with the last two trials in a series before the set change (set unchanged condition). The results indicated changes in central frontal and parietal electrodes during attentional set-shifting. More precisely, the P300 effect was replicated in this dataset, confirming the claim that the WCST measures function of prefrontal cortical areas of the brain. However, the obtained wave resembled P3b indicating the working memory component of the task. The results suggest that the frontal and parietal cortical activity is especially involved in set-shifting during WCST performance. Therefore, these electrophysiological results are not consistent with some recent studies that question the specificity of WCST as a measure of frontal and parietal lesions.     

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.     

The effect of the level of consciousness on the spatial organization of cortical activity in mental processes

In the present study the influence of the level of consciousness on spatial organization of the cortical functional activity in human psychic processes was investigated. For regulation of the level of consciousness models were used of hypnotic analgesia, automatization of intellectual actions and mental activity in hypnotic state. Evaluation of the mosaic of the cortical activity was made by parameters of spatial synchronization of the potentials with topographic mapping of crosscorrelation, spectral and coherent-phasic EEG characteristics. The obtained data allow to conclude about special role of the frontal areas of the left hemisphere in the process of realization of information. It has been shown that one of the main functions in neurophysiological structure of consciousness is the selection of signals according to dominating motivation. The frontal areas of the left hemisphere control the degree of inclusion of foci of increased activity, specific and non-specific for each type of activity, and possibly, regulate the way of transformation of the information.     

Changes in spectral coherent characteristics of EEG in the early postpartum period in mothers with anxious and depressed mood

Postpartum EEG spectral and coherence characteristics were estimated in mothers with or without postpartum depressions. In mothers without affective disorders the power of oscillations in the delta, theta, and alpha 1 frequency bands was increased as compared to controls. Intrahemispheric EEG coherence between the left frontal and adjacent derivations in the delta and theta bands and interhemispheric coherence in the central areas was increased and decreased over the remaining cortical surface. These changes led to a significant decrease in EEG asymmetry. It is suggested that during normal postpartum the influence of the limbicodiencephalic and lower brainstem structures on the cortex is augmented and a certain kind of dominanta is formed. In mothers with postpartum depressions the EEG alpha-band power was lower than in the control and normal groups, coherence changes in the delta and theta bands diminished the EEG asymmetry. The insufficiency of limbicodiencephalic influence and impairment of adaptive brainstem reactions are suggested to be responsible for problems in the formation of maternal dominanta, which results in the development of postpartum depressions.     

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.     

Psychophysiological mechanisms of stress in subjects with different representation of activation

The EEG spectral power was calculated in 102 students aged 18-25 years in three experimental conditions (during the common educational process, immediately before and after an examination). Before the examination (stress situation), predominant activation of the right anterior cortical quadrant (the area related with negative emotions, according to R. Davidson, 1993) was revealed by the asymmetry coefficient of the beta rhythm. Subjects with low amplitude of the alpha rhythm (more activated) manifested not only emotional but also autonomic disturbances, while only emotional signs were pronounced in students with high alpha (less activated). Increase in the theta rhythm spectral power during stress and its decrease in the poststress period were observed in the less activated persons, which is considered to be a normal reaction to emotionally negative stimuli. On the contrary, in students with low alpha the theta rhythm power in the stress situation was decreased pointing to their emotional instability. In this group, as distinct from the first one, the beta 2 rhythm recorded in the right anterior cortical quadrant did not decrease in the poststress situation. Together with the observed theta rhythm, decrease in the left-hemisphere and bilateral prefrontal areas in the stress situation, this deviation testifies to a predisposition to the reactive depression of these subjects.     

The Role of Aerobic Fitness in Cortical Thickness and Mathematics Achievement in Preadolescent Children

Growing evidence suggests that aerobic fitness benefits the brain and cognition during childhood. The present study is the first to explore cortical brain structure of higher fit and lower fit 9- and 10-year-old children, and how aerobic fitness and cortical thickness relate to academic achievement. We demonstrate that higher fit children (>70th percentile VO_2max) showed decreased gray matter thickness in superior frontal cortex, superior temporal areas, and lateral occipital cortex, coupled with better mathematics achievement, compared to lower fit children (<30th percentile VO_2max). Furthermore, cortical gray matter thinning in anterior and superior frontal areas was associated with superior arithmetic performance. Together, these data add to our knowledge of the biological markers of school achievement, particularly mathematics achievement, and raise the possibility that individual differences in aerobic fitness play an important role in cortical gray matter thinning during brain maturation. The establishment of predictors of academic performance is key to helping educators focus on interventions to maximize learning and success across the lifespan.     

Cortical interactions in the beta2-rhythm during examination stress

Two groups of students: with higher and lower amplitudes of the baseline alpha-rhythm differed in the level of anxiety during examinations and the level of cortical interactions. Cognitive tasks were presented in three experimental conditions: before the examinations, immediately after the examinations, and on a usual day of academic semester (control). Subjects with initially higher alpha-rhythm amplitude had lower level of anxiety in a stress situation. Cognitive performance of these subjects before examinations was associated with an increase in the number of functional connections between different cortical areas. In the subjects with initially lower alpha-rhythm amplitude, the level of cortical interactions before examinations was higher, but presentation of the cognitive task led to a decrease in the number of intracortical connections. However, the localization of these connections was task-specific.     

Spectral characteristics of EEG during formation a set to illusory length perception (Müller-Lyer illusion)

A cognitive set to illusory perception of linear relationships was formed in 56 young healthy subjects. After 10 presentations of Müller-Lyer figures, 39 subjects formed the stable set. In 17 subjects the unstable set was formed. The spectral power of the EEG led from different cortical areas was studied at different stages of set formation. Analysis of variance showed that the factors "set stage" and "group" x "set stage" x "hemisphere" exert significant influence on the EEG spectral power in the delta range in the frontal area. In the subjects with stable set, the power of this spectral component increased at the stages of set formation and actualization and returned to its initial values during set extinction. The between-group difference was more expressed in the left hemisphere. In subjects, which formed the stable set, the power of the occipitotemporal alpha rhythm in the reference state was higher than in subjects with the unstable set. In the process of set formation, the dynamics of the alpha spectral component (8-10 Hz) was more expressed in the stable group: its power increased to a greater extent at the stages of set actualization and extinction. In both groups, there were no significant changes in the alpha2 power over the course of the experiment.     

Changes in the P300 amplitude under the influence of "aggressive" computer game in adolescents with various levels of initial aggression and conflicting behavior

Dynamic changes in the amplitude of component P300 of the evoked potentials in different cortical areas were studied as an index of activity of cortical structures responsible for actualization of a computer game with aggressive content with regard for the level of initial aggression and conflict in behavior of adolescent subjects. Dynamic changes in anxiety and aggression evoked by playing an "aggressive" computer game were shown to be dependent on the initial level of aggression and conflict. An increase in P300 in the frontal and orbitofrontal areas of both hemispheres was observed in adolescents with initially high level of aggression and conflict. In adolescents with initially low aggression and conflict, P300 decreased bilaterally in the frontal areas and did not change significantly in the orbitofrontal areas. These findings testify to the bilateral frontal top-down control over negative emotions.     

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.     

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.     

Rat brain reactions to acute brain stem lesion on dynamics of parameters of cerebral electric activity

Despite an old history of a question, adaptive brain reactions that develop after an acute brainstem lesion have not been adequately investigated. With the aim to study the central mechanisms of compensation/decompensation and to specify the character of involvement of orbitofrontal cortex and hippocampus into these processes the spatiotemporal organization of brain electric activity was analyzed in 8 rats before and after electrolytic brainstem lesion at the level of the lateral vestibular nucleus Deiters (VND). The electric activity was recorded from symmetric frontal and somatosensory cortical areas, hippocampal areas CA1, and intact VND. Spectralcoherent analysis showed that adaptive reactions are most clearly manifested by changes in the spatiotemporal organization of the theata activity: 1) early brainstemhippocampal synchronization of the electric activity in the frequency range of 6-7 Hz with subsequent involvement of anterior cortical regions is characteristic of survived animals; 2) independent hippocampal-cortical hemispheric system of excitation in the frequency of 4-5 Hz precedes the fatal outcome. On the day before the fatal outcome the interhemispheric coherence in the orbitofrontal cortex dropped, which suggests the involvement of these brain regions into the processes of visceral regulation.     

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.     

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.