ORIGINAL ARTICLEThe paper presents finding of an experiment the aim of which was to judge the impact of an instant cognitive activity (identical pictures searching) on behavior of ongoing EEG activity. Two types of mental task were used: The first -passive watching of a blank white oval and the second -active searching for identical pictures in a group of similar nine line-drawings of living individuals or inanimate objects filling out the white oval.Presented results showed that higher mental load pertinent to active searching for identical pictures in a group of similar pictures results in the prominent event-related desynchronization (ERD) -the mean Total Power value, a quantitative measure of ERD extent, in comparison with reference level (passive watching) was lower while solving the mental task.The results also showed that the actual mental task performance affects the ERD only at some scalp-recording sites. The mean EEG Total Power significantly decreases at parietal and frontal scalp-recording sites whereas the significant decrease of the Frequency at Maximum Power involves occipital scalp electrodes, too.Our results also demonstrated that some subject's personality traits (moderation, openness and extraversion) affect the actual decrease/increase in size of Frequency at Maximum Power during active mental task solving.Presented findings point at the high suitability of the ERD method to uncover differences in people's brain activation patterns when engaged in performing cognitively demanding tasks.

Event-related potentials (ERPs) to word stimuli were registered in 20 twenty-one-year-old students (7 males and 13 females) of the Faculty of Medicine of Palacký University. In an ideal case in the first 800 ms after the onset of stimulus ERP consists of three clear positive and four negative waves. The amplitude of some waves of ERPs shows a high degree of inter-individual variability. It was also revealed that the latency and amplitude of some ERPs waves to word stimuli depends on the gender and on the site of the registration electrode on the scalp of the subject. Latencies of components LP2 and LN4 in all electrodes are shorter in females than in males, component LN2 behaves reversely--its latency is shorter in males. On the other hand, the amplitude of dependent variables BP2, BN2 and PV1 is in most electrodes higher in females than in males--except for the amplitude of components BP4 and BN1.

Aims:To judge whether and how the character of the visual stimulus and type of cognitive task aff ects brain eventrelated potentials (ERPs).Methods: ERPs to three types of visual stimuli (white blank oval on a dark background, unfolded cube and net of sixteen small squares) were recorded from nine scalp sites and saved on a computer. Special software was used for off -line analysis of the ERPs.Results: The presentation of each of the three visual stimuli used was followed by ERPs consisting of two negative (N160, N340) and one positive (P220) components. The character of the stimulus did not aff ect the latency of ERPs components. However, the type of visual stimuli aff ected the amplitude. The most conspicuous changes were shown by the N340 ERPs component. Its average amplitude in comparison with reference amplitude was always significantly higher during the fi rst cognitive task ("Choose the cube that can be folded up from the unfolded cube!") and signifi cantly lower than reference amplitude during the second cognitive task ("Complete the missing part of a fi gure with the appropriate item!"). It was also shown that subjective personality traits such as nervousness, spontaneous aggressivity and emotional lability had an infl uence on the recovery phase of the experiment aff ecting the average amplitude of N340 Conclusion: The results revealed that the cognitive processes underlying successful resolution of two pictorial cognitive tasks aff ected diff erently the activity of systems giving rise to visual ERPs.

The present findings show the existence of significant differences in latency and amplitude of some waves of ERPs to three subclasses of nouns or verbs. Latency LP3 of ERPs to action verbs was shorter than latency of the same wave to abstract verbs. In nouns the relation was a similar (manipulable objects versus abstract ones). The amplitude of early positive components (P1, P2) and BN3 wave also depended on semantic attributes of nouns and verbs. Some waves of ERPs to motion verbs in our experiment had significantly higher amplitude than the same waves of ERPs to nonmanipulable objects. Also revealed was interaction between some ERP features and the subject's gender. It was primarily the amplitude of BP2, the size of which depended on gender in all cases--BP2 amplitude was significantly higher in females then in males. In the other components (BP1, BP4, BN2 and BN4) there were fewer significant differences and if they do occurred, then their amplitude was higher in males than in females. In some cases, gender also affected latency of waves LP2, LN1 and LN4 of ERPs to the same noun or verb subclass--latencies of these waves were shorter in females.