[Functional organization of the cerebral cortex during preparation to recognition of incomplete linedrawings in 7-8 years-old children and adults].

Functional interaction between prefrontal, temporal and tempo-parieto-occipital zones during preparation to recognition of incomplete linedrawings were analyzed in adults (n = 26) and children of 7-8 years old (n = 20). The strength of cortico-cortical interactions was estimated with the imaginary part of the complex-valued coherence at the frequency of alpha-rhythm (Jα). The Jα value was analyzed in the following three experimental conditions which corresponded to different stages of preparation to visual recognition: nonspecific sustained attention in the period preceding the cue (C1); focused attention in the period preceding a not-yet-recognized target stimulus (C2) and focused attention prior the successfully recognized stimulus (C3). When sustained attention changed to focused attention toward a target stimulus Jα increased in adults but decreased in children. Comparing Jα in the subgroups of both adults and children that showed highest recognition scores helped to uncover the age-related pattern of rearrangement of the cortico-cortical functional interactions in alpha-rhythm. That pattern was found to be hemisphere-specific and different at different stages of preparation to recognition of incomplete linedrawings. In adults, the maximal Jα were found in the left hemisphere during the period preceding the recognition of a target stimulus. At this stage of the functional preparatory tuning, in adults, Jα in the left hemisphere was significantly greater than in children. In adults, Jα related to the right hemisphere attained the highest values when attention was directed to not-yet-recognized stimuli. These values were significantly higher than similar values measured in children. In children, Jα reached its highest value during sustained attention. The characteristic pattern of functional interactions among prefrontal, temporal and temporo-parieto-occipital cortices that observed in children of 7-8 years old during preparatory functional tuning for the recognition of incomplete linedrawings is considered to be an indication of relative immaturity of mechanisms of directed voluntary attention and working memory.

[The functional brain organization during preparation for recognizing incomplete images].

The functional interaction between prefrontal cortex and other cortices was analyzed during the pre-stimulus period in the task in which human subjects (n = 36) were asked to recognize a set of incomplete images of different degree of fragmentation. The imaginary part of the complex-valued coherency was used to measure a strength of inter-area coupling at the alpha-rhythm frequency. Based on the analysis of individual responses the two equal sub-groups (n = 13) showing the lowest and highest recognition scores were extracted from the whole group of subjects. It is shown that the pattern of the functional cortico-cortical interactions as well as the direction of its' changes differ in the two sub-groups. In those subjects who successfully solve the cognitive task, the changes in functional connectivity indices in the situation of focused attention are most pronounced in the right hemisphere if stimulus-to-come would not be recognized. Period preceding recognized stimulus is characterized by the increased cortico-cortical coupling in the left hemisphere. In that sub-group, the values of imaginary part of alpha-coherency show the growth in both hemispheres when the period of focused attention is compared against the period of nonspecific attention. On the contrary, the similar comparison for the sub-group of the least successful subjects shows the imaginary coherency decreases in both hemispheres. These results suggest the constructive role of the alpha-rhythm in functional assembling the prefrontal cortex during the period that precedes the recognition of incomplete images.

[Frontal bilateral synchronous theta-waves and the resting EEG coherence in children aged 7-8 and 9-10 with learning difficulties].

The resting state cortical functional connectivity was studied in children of 7-8 (N = 29) and 9-10 (N = 23) years with learning difficulties whose EEG showed the frontal bilateral synchronous theta waves (FTW) and in the control children of 7-8 (N = 32) and 9-10 (N = 16) years who did not experience school difficulties and whose EEG did not show signs of abnormality. The functional connectivity was estimated in the theta, alpha1, alpha2, and beta1 frequency bands via measuring the coherence for the resting EEG that was free from any abnormal patterns. Compared to control children, there was a reduction in the strength of the functional coupling between the frontal and anterior temporal cortices found predominantly in the left hemisphere of FTW children. The relative weakness of the coupling between the frontal cortex and the other cortical areas was more pronounced in children of 7-8 than in children of 9-10 years. These between-group differences were unaffected by the frequency band or gender factors.

[Bilateral frontal theta-waves in EEG of 7-8-year-old children with learning difficulties: qualitative and quantitative analysis].

We analyzed EEG recorded in the rest condition (eye closed) in 22 children aged from 7 to 8 years old who experienced learning difficulties and whose EEG recordings were characterized by sporadic short-term appearance of bilateral synchronous slow waves over the frontal and/or central cortices--frontal theta-waves (FTW). The vector autoregressive modeling was used in order to assess the strength of directed cortico-cortical functional connectivity pattern for FTW and for surrounding EEG. The comparison of the two patterns showed that FTW is characterized by diffuse strengthening of the functional links connecting frontal, central and (to some extent) temporal cortices as well as the links directed to the above regions from the other cortical areas. The results of the study suggest that FTW is most probably caused by the common for the fronto-central cortices neuronal theta activity synchronized via cortico-subcortical links. This suggestion is in a good agreement with the view that FTW reflects the alterations in functioning of fronto-thalamic system.

[A comparative electrophysiological study of regulatory components of working memory in adults and children of 7-8 years old. An analysis of coherence of EEG rhythms].

Coherence at the frequency oftheta, alpha, and beta EEG rhythms was analyzed in 14 adults and 23 children of 7-8 years old while they performed cognitive tasks requiring an involvement of working memory (WM). We used the pair matching paradigm in which subjects had to match a pair of stimuli shown in succession in the central visual field. The pairs of verbal and visuo-spatial stimuli were mixed together and presented in a pseudo random order. Each pair was preceded by a warning signal that did not specify a modality of upcoming stimuli. We analyzed EEG segments recorded (i) in the rest condition, (ii) prior to the first (etalon) stimulus (maintenance of nonspecific voluntary attention), and (iii) prior to the second (test) stimulus (retention of information in WM). In the present study we focused on the regulatory functional components of WM, and therefore, the stimulus modality has not been taken into account. In adults, maintaining nonspecific voluntary attention was accompanied by an increase of the strength of theta-related functional coupling between medial areas of the frontal cortex and temporal cortical zones and by a strengthening of local beta-related functional connectivity in the anterior areas of the central cortex. In children, no such increase was found for theta-rhythm; for beta-rhythm the increase was limited to several short-range functional links. In adults, the retention of information in WM was accompanied by the growth in alpha coherence in distant fronto-parietal links, predominantly in the right hemisphere, while in children information retention was accompanied by the growth of theta-coherence in the inferio-temporal and parietal cortical regions. The results of the study point to a relative immaturity of the mechanisms of executive control of WM in children of 7-8 years old.

[Specific features of regulatory and information-related components of cognitive processes in 7-10-year-old children with local EEG abnormalities in the right hemisphere].

Two groups of 7-10-year-old children were formed on the basis of the results of visual analysis of their EEG. The first group included 15 children with local EEG deviations in the right hemisphere, and the second group included 21 children without EEG deviations from the age norm (control group). In both groups, verbal and nonverbal higher mental functions and the ability to voluntary control of activity were assessed by means of neuropsychological methods. As compared to children of the control group, children with local EEG deviations in the right hemisphere demonstrated some difficulties in strategy formation, reduced ability to maintain already formed programs, increased fatigue, changes in affective behavior (anxiety and behavioral excitability), deficit of visual and somatosensory perceptual synthesis, reduction in object recognition efficiency, and visual memory deficit.

[Functional brain organization of global and local visual perception: an ERP study].

Adult subjects were asked to recognize a hierarchical visual stimulus (a letter) while their attention was drawn to either the global or local level of the stimulus. Event-related potentials (ERP) and psychophysical indices (reaction time and percentage of correct responses) were measured. An analysis of psychophysical indices showed the global level precedence effect, i.e., the increase in a small letter recognition time when this letter is a part of incongruent stimulus. An analysis of ERP components showed level-related (global vs. local) differences in the timing and topography of the brain organization of perceptual processing and regulatory mechanisms of attention. Visual recognition at the local level was accompanied by (1) stronger activation of the visual associative areas (Pz and T6) at the stage of sensory features analysis (P1 ERP component), (2) involvement mainly of inferior temporal cortices of the right hemisphere (T6) at the stage of sensory categorization (P2 ERP component), and (3) involvement of prefrontal cortex of the right hemisphere at the stage of the selection of the relevant features of the target (N2 ERP component). Visual recognition at the global level was accompanied by (1) pronounced involvement of mechanisms of early sensory selection (N1 ERP component), (2) prevailing activation of parietal cortex of the right hemisphere (P4) at the stage of sensory categorization (P2 ERP component) as well as at the stage of the target stimulus identification (P3 ERP component). It is suggested that perception at the global level of the hierarchical stimulus is related primarily to the analysis of the spatial features of the stimulus in the dorsal visual system whereas the perception at the local level primarily involves an analysis of the object-related features in the ventral visual system.

[EEG spatial synchronization at different set stages in 8-year-old children with different levels of selective attention fronto-thalamic system maturity].

Visual cognitive set was studied in two groups of 8-year-old children: with normal development of fronto-thalamic system (FTS) (n = 21) and with functional immaturity of this system (n = 29). In most of the children with the FTS-immaturity a formed visual set was rigid. EEG was recorded from the frontal, central, temporal, parietal and occipital regions, and coherence function in theta-, alpha- and beta-bands was analyzed. The most vivid differences between two groups of children were revealed at the set actualization stage. If the set was a plastic one, the value of coherence function between frontal and dorsal areas was higher in children with FTS-immaturity, than in "normal" ones. In the group with FTS-immaturity the dependence of coherence function on the set's plasticity was more vivid, than in children without FTS-immaturity. In all children with a rigid set value of coherence function was higher during set formation, actualization and extinction, than at resting condition with eyes opened. In the group with FTS-immaturity the coherence of theta-band considerably increased at the set actualization stage, mainly in the right hemisphere. We consider this to be the evidence of a comparatively bigger role of cortico-hippocampal system and implicit episodic memory the set shifting. Probably these processes compensate the FTS-dysfunction and make a set more plastic.

[Developmental changes in hierarchical visual stimulus recognition in children aged 5-10 years].

Reaction time (RT) and performance accuracy in hierarchical visual stimulus recognition at local and global levels were studied in 95 healthy 5-6, 6-7, 7-8 and 9-10-year-old children and 10 adults. Task performance of all examined subjects, both children and adults, was faster and more accurate during global feature recognition (global advantage effect), with increased RT to incongruent stimuli in local condition (global interference effect). Significant inter-individual differences were found in the youngest group (5-6-year-olds): 7 children from the total number of 37 subjects failed to show the global advantage and global interference effects. Significant progressive shifts in performance accuracy during hierarchical stimulus recognition at both local and global levels were observed in the period between 6-7 and 7-8 years and then between 9-10 years and adulthood. The time course of age-dependent changes in recognition time was different for the global and local features of the hierarchical stimuli: the RT significantly decreased in every successive age group for local feature recognition beginning from 6-7-year-old children, whereas there was no significant difference between 7-8 and 9-10-year-old children in the RT of the recognition of the global feature. In the two younger groups (5-6 and 6-7 years), the stimulus type affected performance in a specific manner: RT increased to both incongruent and neutral stimuli irrespective of the level of the target feature. It was assumed that nonlinear developmental trends in hierarchical stimulus recognition parameters depend on both maturation of visual information processing and development of executive functions, especially those related to selection of relevant signals.

[Functional coupling of cortical areas during problem-solving task: an analysis of theta rhythm coherence].

We analyzed the EEG theta rhythm coherence in adult subjects who performed visual object classification task in the condition of uncertainty. The coherence function was estimated for the EEG segment following a feedback signal. It was shown that the functional coupling of cortical areas was stronger in the process of strategy discovering as comparing to the final period when the strategy is already found. The theta-related functional links are characterized by a specific topographical pattern: they converge to the foci located in the polar frontal cortex and reflect the interaction between the latter and the anterior associative cortices of the left hemisphere and occipital areas of both hemispheres. This pattern of functional connectivity may reflect an interaction between limbic structures and the frontal cortex in the process of strategy formation.

[Individual differences in global vs. local visual perception of hierarchical stimuli under conditions of free and forced recognition].

Sixteen adult subjects were asked to recognize hierarchical letters at either local or global levels. The experiment included two sessions, corresponding to free recognition and forced recognition with the attention directed to a specific level of hierarchy. The analysis of recognition errors and reaction time in the condition of free recognition revealed two individual strategies of visual perception: the "global strategy" (the global level was chosen more frequently) and the "local strategy" (the local level was chosen more frequently). In the condition of forced recognition, the subjects who preferred the "global strategy" demonstrated the expected "global interference effect". The representatives of the "local strategy" showed the inversion of this effect, i.e. their reaction time significantly increased during recognition of the conflict stimuli at the global level.

[Visual set and shifting of selective attention in 8-year-old children with EEG-signs of immaturity of fronto-thalamic and brainstem activating systems].

Visual set (by D.N.Uznadze) was studied in three groups of 8-year-old children: children with EEG-signs of immaturity of fronto-thalamic activation system; children with a deficit of non-specific activation from mesencephalic reticular formation; children with normal development of these systems (control group). Children with a deficit of non-specific activation split in two groups: one group was similar to the control group in set-forming, set-shifting and response time dynamics; another group haven't displayed a set actualization stage and had a considerably bigger response time during attention shifting. Children with immaturity of fronto-thalamic system, when compared to the control group, had considerably more contrast illusions at set-testing stage and considerably bigger response time during attention shifting at set actualization stage. These data suggest a participation of fronto-thalamic system in set-forming and set-shifting.

[Spatial organization of the cortical electrical activity at different stages of visual set in children of preschool and junior school age].

Set-forming and set-shifting were studied in children of three age groups: five to six-, six to seven- and nine to ten-year-old. Set effect displayed itself in contrast illusions in most of the subjects (69 of 73). Age differences in set plasticity and in reaction time to a probe stimulus were revealed. Five to six-year-old children formed a more rigid set than older ones. According to EEG coherence function in theta- and alpha-bands and behavioral data, a hypothesis of two systems being involved in set-forming and set-shifting is proposed. These systems are: a fronto-talamic system of selective attention, and a system of cortico-hippocampal connections that are involved in cortical processing of novel visual information and in episodic memory. The age of 6-7 years is shown to be critical in forming a plastic type of cognitive set.

[Spatial synchronization of cortical electrical activity at different stages of visual set in preschool children].

Changes in the alpha-rhythm synchronization were revealed at different stages of cognitive visual set in 5- to 7-year-old children. We found a clear-cut correlation of these changes with set plasticity. In children with a plastic set, the EEG synchronization between the frontal and other brain regions substantially increased in the period of set-shifting (the actualization stage). At the set extinction stage, after set-shifting has already taken place, the EEG-synchronization becomes minimal. On the contrary, in children who formed a rigid set, EEG coherence considerably increases at the set extinction stage. This finding suggests that the rigid set still affects the cognitive activity even after (judging from oral reports) the set shift has been completed. The age-related differences in cognitive set formation clearly correlate with the time course of the EEG synchronization between the frontal and other brain regions. We think that the ability to form a plastic visual set depends on the frontal cortex maturation, which occurs at the age of 6-7 years, and its age-related effect on the brain cognitive functions.

[Characteristics of attention in children with attention deficit hyperactivity disorder (an analytical review)].

The information concerning specific features of different attention components (alertness, sustention and selectivity) in children with attention deficit hyperactivity disorder (ADHD) is analyzed and systematized. According to the data reviewed, behavioral and attention problems described as ADHD are not homogeneous. Literature analysis of attention characteristics in children with ADHD shows that different components can be disrupted if ADHD is diagnosed as inattentive or combined subtype, but the main deficit in this case is that of selective voluntary attention. In case of hyperactivity/impulsivity subtype of ADHD, attention is impaired mainly in its brain activation components.