Kuznetsov I. Cognitive activity electroencephalography peculiarities in conditions of left- and right-handedness

The study was held on 159 persons, who were divided into two groups: righthanders (80 persons) and left-handers (79 persons). For the sex peculiarities study each group was divided into two subgroups (4 subgroups total): male-righthanders (40), female-righthanders (40), male-lefthanders (39), female-lefthanders (40). The study was carried out on the computer EEG-system "DX-5000 Practic". The following experimental situations were used: the background EEG (relaxation state), the look fixation, the photostimulation, the graphic-spatial testing, the anagrams and the mathematical tasks solving, the simple movements with right and left hand on photostimulus (the light flash). Native EEG was automatically processed with the Fast Furies Transfer with the general EEG-bands representation, the intensity and correlations between brain lobes calculation. The obtained data were statistically processed. In our study there were the data from frontal, temporal, central, parietal and occipital lobes in right and leftbrain hemispheres investigated. Left-handers have the more generalized activation processes. This feature is accompanied by the less evident interhemispheric asymmetry. This phenomenon can be explained by the different language centers location in the cortex of right- and left-handers. Right-handers have the more localized higher activity focus - in the back-associative brain zones during nonverbal tasks and in the front-associative brain zones during cognitive tasks. Moreover, left-handers have a higher frequency of general EEG-activity. Both the generalized activity and the higher EEG frequency may be the evidence of a more variable and more exhaustive cognitive work. Is is also possible that left-handers have a higher strength and lability and lower steadiness of nervous processes. The increase of the subjective task difficulty is accompanied by the brain activity generalization. The cognitive tasks grade the differences in the EEG-bands representation between right- and lefthanders. During the mathematical testing both left-handers have a high activity in both temporal lobes, while in the right-handers group the only right temporal lobe shows high activity. This is the result of the correlation links and EEG-bands intensity analysis. In the beta- and theta-bands lefthanders have significantly higher intensity of the left central lobe during noncognitive (except tests with simple hand movements) and cognitive tasks. This feature is more typical of left-handed males. Thus, left-handers have a more explicit brain electric activity generalized type, both under the verbal and the nonverbal activity. As the general brain electric activity indexes show, right-handers have a more expressed functional asymmetry of brain hemishperes. The peculiarity of the left-handers brain functioning is the higher EEG-components frequency in comparison with right-handers. This is more typical of left-handed males. It indicates that theta- and beta-EEG-bands are more susceptible to manual asymmetry.