Correlation between Cognitive Performance and Interhemispheric Asymmetry of EEG Alpha Rhythm during Lateralized Presentation of Visual Information against the Background of Optical Stimulation.

The effect of lateralized optical stimulation with a frequency of 10 Hz on the effectiveness of cognitive task performance (n-back test) was studied in 33 healthy subjects (right-handed men). Test visual information was presented to the right or left visual hemifield under normal conditions and against the background of optical stimulation with a frequency of 10 Hz. The absolute values of the spectral power of the high (10-13 Hz) subrange of alpha-rhythm of EEG (SPα2) were calculated. When test information was sent to the right hemisphere against the background of stimulation, an increase in task performance was revealed in subjects with low SPα2. This was accompanied by an increase in SPα2 in some cortical areas of the contralateral (left) hemisphere and, as a result, an increase in left-side dominance of SPα2. The findings indicate the possibility of using lateralized optical stimulation to improve cognitive task performance, in particular, by changing the interhemispheric asymmetry of the EEG alpha2-rhythm.

Influence of Rhythmically Organized Optical Stimulation on the Performance of Human Cognitive Activity and Spatial Characteristics of the EEG Alpha Range.

We studied the effect of optical stimulation with a frequency of 10 Hz on the cognitive task effectiveness (the "n-back" test) and spatial characteristics based on the coefficients of coherence (Coh) of the general, high, and low ranges of the EEG alpha rhythm in healthy subjects (38 men aged 18-26 years). Based on the performance of the test presented in the optical stimulation absence, groups with high (group 1) and low (group 2) results have been identified. It was found that the optical stimulation led to a decrease in the test effectiveness in group 1 subjects and to an increase in group 2 persons. Optical stimulation increased interhemispheric integration of neural ensembles in a number of cortical areas at frequencies of a high subrange of the alpha rhythm. An increase in interhemispheric cooperation was more characteristic of subjects who increased the test activity effectiveness against the optical stimulation background. It is assumed that the growth of interhemispheric integration caused by rhythmically organized 10-Hz optical stimulation is a factor contributing to an increase in the effectiveness of performing cognitive tasks of this kind.

Analysis of Endogenous Spectral Power of EEG Alpha-Range Biopotentials during Mnestic Activity under Conditions of Rhythmically Organized Optical Stimulation.

We studied the effect of optical stimulation (10 Hz) on the effectiveness of mnestic activity in the n-back task in healthy subjects (n=32). EEG was recorded at all stages of the examination. The absolute values of the spectral power of the 10 Hz frequency (µV2) of the alpha range were calculated. According to the results of the test without optical stimulation, the examinees were divided into groups with high (group 1) and low (group 2) task performance. In the initial state, the spectral power of 10 Hz was significantly higher in group 1 subjects. Under conditions of screen flickering, the results became poorer in group 1 and better in group 2 in comparison with the results under normal conditions. These changes were accompanied by an increase in the spectral power of 10 Hz only in group 2 subjects. These findings can provide the basis for the development of practical recommendations for improving the mnestic functions in patients with consideration for the individual characteristics of their initial EEG.

Spatial Organization of Alpha Range Potentials on EEG and Logical Thinking Effectiveness.

We studied spatial organization of EEG alpha range potentials in volunteers with different results of tasks requiring logical thinking. The examinees with higher cognitive test performance have more labile coherent associations of EEG alpha range potentials, which manifested in changes in the level and structure of these associations at different stages of the test. In individuals with poor results, the number of significant coherent associations and their structure do not change during the problem solving process.

[Dynamics of EEG Alpha-Activity and Heart Rate Variability in Subjects Performing Cognitive Tests].

Changes in the power and coherence of α-activity and heart rate variability (HRV) were studied in students with different performance levels in logical tasks. In those students who reached high scores in the cognitive tests, we observed higher lability of α-activity and HRV; the values and their ratios varied among the stages of intellectual activity. In these subjects, a decrease in the spectral power of α-band was more pronounced than in other groups. We also observed changes in the interhemispheric coherence and in the structure of coherent interactions in the α-range at different stages of task performance. In contrast, the number and structure of coherent interactions in individuals who showed lower results did not significantly vary at different stages of task performance. As compared with this group, the students with higher test results showed a more pronounced decrease in the total spectral power (TP) and an increase in the low frequency/high frequency (LF/HF) ratio which returned to the initial level after the end of the tests. In students with better results in these cognitive tests, the dynamics of RRNN, TP, HF, and LF/H F during task performance correlated with the dynamics of interhemispherical α-band coherence.

Dynamics of heart rhythm characteristics and efficiency of intellectual activity during computer work.

Heart rhythm variability characteristics were studied in volunteers with different stability of the results upon switching from one type of intellectual activity to another. Individuals with stable results differed from those with worse accuracy of information reproduction by high initial CV, total power of heart rhythm variability and power of VLF, LF, and HF spectra. Volunteers with stable results were characterized by high lability manifesting by changing values and proportions of heart rhythm variability characteristics at different stages of activity and by the absence of a relationship between these parameters at different stages of activity and initial status of the volunteer. VLF spectrum power decreased with impairing the accuracy of information reproduction.

[Motivation effect on EEG spectral power and heart rate parameters in students during examination stress].

EEG spectral power was calculated in 24 students (18-21 years) with different levels of motivation and anxiety (tested by Spielberger) in two experimental conditions: during the common educational process and the examination stress. Before examination tests, in subjects with high motivation and anxiety level the relative delta activity power increased in right frontal (F4) brain areas. In students with medium motivation immediately before an examination the relative beta2-activity power increased in right frontal (F4) brain areas. It is suggested that delta oscillati- ons reflect activity of the defensive motivational system, whereas beta2 oscillations may be associated with the achievement motivation.

[Spatial organization of the beta2 EEG frequency band and effectiveness of the intellectual activity in humans].

Features of spatial organization of the beta2 EEG frequency band were studied in subjects with different speed and accuracy during task performance of the memorizing and subsequently reproducing of the sequence of signals on monitor screen. Students who had reached a high speed and accurately performed intellectual tasks were characterized by high lability of the coherent relations in the beta2 EEG range, which manifests itself in a significant coherence increase during memorization and reproduction of the signal sequence compared to the initial state. In contrast, in individuals who needed more much time for making decisions and mistakes, the number and structure of coherent relations from stage to stage of activity considerably did not change.

[Geometrical images of coherent interrelations of biopotentials of EEG different frequency ranges in dynamics of humans goal-directed behavior].

Spatial organization of teta, alfa, beta-1, beta-2 in EEG potentials in humans who quickly an with a high accuracy performed task to learn and reproduce on PC monitor a definite sequence o accuracy performed task to learn and reproduce on PC monitor a definite sequence of circles wer studied. It was found that geometric images of coherent interrelations of teta, alfa, beta-1, beta-2 in EEG potentials were dynamically changed on the different stages of goal-directed the humans activity. The studies give the grounds to consider dynamically changed geometrical images of coherent links of different EEG potentials as an objective index of external projection of intracerebral processes of system architectonics of goal-directed behavior on brain cortex.

Spectral-coherent characteristics of EEG alpha rhythm in different efficiency of visual spatial task performance in humans.

We studied spectral-coherent characteristics of EEG alpha rhythm in 26 students demonstrating different performance efficiency in visual spatial tasks of the same difficulty. More close coherence of biopotentials in the alpha EEG frequency band was observed between the occipital, parietal, central, and temporal areas in both hemispheres of the brain. The results of the experiments showed that different performance efficiency in visual spatial task of the same difficulty was associated with different levels of biopotential synchronization in the EEG alpha frequency band.

[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.

[Geometric imaging of coherent interrelationships of electroencephalogram α-rhythm in dynamics of system effective human activity].

In subjects performing tasks quickly and precisely, geometric imaging of coherent connections among the EEG alpha-range potentials dynamically changed and turned out to be specific for each of the intended activity's stages. In the subjects performing tasks slowly and with errors, in different stages of effective human activity, a stability of the geometric image was observed. The revealed geometric imaging changing in different stages of effective activity seems to reflect a multi-level organization of the action results acceptor.

[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).

[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).