[Brain Organization of the Preparation for Visual Recognition in Preadolescent Children].

The brain organization of the process of preparation for the perception of incomplete images fragmented to different extents. The functional connections of ventrolateral and dorsoventral cortical zones with other zones in 10-11-year-old and 11-12-year-old children were studied at three successive stages of the preparation for the perception of incomplete images. These data were compared with those obtained for adults. In order to reveal the effect of preparatory processes on the image recognition, we also analyzed the regional event-related potentials. In adults, the functional interaction between dorsolateral and ventrolateral prefrontal cortex and other cortical zones of the right hemisphere was found to be enhanced at the stage of waiting for not-yet-recognizable image, while in the left hemisphere the links became stronger shortly before the successful recognition of a stimulus. In children the stage-related changes in functional interactions are similar in both hemispheres, with peak of interaction activity.at the stage preceding the successful recognition. It was found that in 11-12-year-old children the ventrolateral cortex is involved in both preparatory stage and recognition processes to a smaller extent as compared with adults and 10-11-year-old children. At the same time, the group of 11-12-year-old children had more mature pattern of the dorsolateral cortex involvement, which provided more effective recognition of incomplete images in this group as compared with 10-11-year-old children. It is suggested that the features of the brain organization of visual recognition and preceding preparatory processes in 11-12-year-old children are caused by multidirectional effects of sex hormones on the functioning of different zones of the prefrontal cortex at early stages of sexual maturation.

[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.

[On the age-related trends in using sensory information in movement organization].

In the present paper, two apparently contradictory developmental trends routinely found in developmental experimental studies are discussed. One of them is the reduction in relative usage of sensory information in movement control; the other (reverse) trend is that, along the course of development, the sensory information plays increasing role in movement organization. An analysis of experimental data suggests that these two trends can be considered as two mutually related overt consequences of the growing ability to build internal models of the processes in the external world and those within the motor system.

[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.

[Quantitative measures of cortical functional connectivity: a state-of-art brief survey].

This par reviews modern approaches to measuring cortical functional and effective connectivity in neurocognitive networks--the large-scale distributed systems of interacting neuronal populations which are thought to underlie the cognitive processing. Two broad classes of methods of connectivity estimation, linear and nonlinear, are discussed. In the class of linear methods, besides the coherence that is routinely used for measuring the strength of functional links, the vector autoregressive modeling of multichannel EEG is discussed in some details. The latter technique allows for estimating both functional and effective connectivity with such measures as directed transfer function (DTF) and direct partial coherence (PDC) which are commonly used in cognitive neuroscience. The impact of volume conduction onto the different estimates of connectivity is considered. The imaginary part of the complex-valued coherence as a way to reduce the artificial influence of volume conduction is also discussed. In the class of nonlinear methods, the Independent Component Analysis and the Transfer entropy as a method of estimation of directed influence are reviewed.

[Internal representation of movement sequences built upon either static line drawings or trajectories of moving object].

In this paper, we explore the issue of the nature (perceptual, abstract, or motor) of neural codes used by CNS in order to store the internal representation of elements of a sequence of movements. Reported are the results of two experiments in which two independent groups of 16 right handed adults repeated, after a given delay, the piecewise trajectories (open polygonal chains) using the graphical tablet. A trajectory was shown either as a static line-drawing (static mode) or a small moving pointer (dynamic mode). The results show that: 1) for the delay varying from 0 to 1 s, the latent time of the trajectory production is greater in the dynamic than in the static mode, with the latent time is no different under to presentation conditions when the production delay reaches 3 s; 2) the latent time is exponentially decaying as the trajectory production delay increases from 0 to 3000 ms, with the characteristic decay time being different in the static (377 ms) and the dynamic (656 ms) presentation modes. The results of the present study are in line with the view that the internal representation of the sequence of movements is perceptual and it is converted into the motor codes at the later stages prior to movement execution. It is suggested in the paper that the observed exponential decay of the latent time might be related to the transformation of the early sensory (iconic) representation into the perceptual trajectory representation.

[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.

[Visuo-motor synchronization in children of 7-8 years old].

The group of 22 children of 7-8 years old and the group of 17 adults participated in the experiment in which they were asked to synchronize their movements (pressing a button) with an isochronous sequence of visual stimuli. The period of the sequence was varied between 500 to 2000 ms with the 300 ms step. Two successive phases of visuo-motor synchronization were studied: the synchronization phase and the initiation phase which corresponds to the process of transition between reacting to a visual stimulus and the stable synchronization. The initiation phase was characterized by the shape and duration of the asynchrony time course (relaxation curve). The statistical properties of asynchrony were analyzed in the framework of the phase correction of the central timer. It is shown that (1) the range of successful visuo-motor synchronization is narrower in children of 7-8 than in adults and it spans from 600-700 ms to approx. 1700 Mc; (2) The initiation phase lasts about the same time in children of 7-8 and adults and typical shapes of individual relaxation curves are similar in both adults and children. (3) Although the statistical properties of asynchrony are comparable in children and adults, the mechanism of phase correction of the central timer operates with a lower value of the correction gain factor in children than in adults. In children, the phase correction process is also characterized by a substantially higher level of the central and motor noise which leads to a higher asynchrony variability and more frequent and longer lasting synchronization losses.

[Age-related trends in spatio-temporal structure of simple graphic movements performed in a cyclic manner at a maximal tempo. Part I. Tempo increase is accounted for by a reduction in the number of submovements in a movement cycle].

Right-handed human subjects of 4 different ages (5-6, 8-9, 11-12 yo. and adult subjects) performed simple graphical movements in a cyclic manner with maximal possible tempo. The movements differed with respect to their coordination and serial complexity and were performed by each hand while holding the stylus either by the fingers or the fist. It was found that cycle duration considerably decreased with age from the age of 5 to adulthood and the amount of the age-related gain in the performance rate depended on which hand (right vs. left) and/or grip (fingers vs. fist) was used to perform a movement. The rate of successive submovements neither changed substantially with age nor showed any lateral asymmetry however it did depend on the movement being performed and the grip being used. The results show that the age-related trend in the cyclic movements can almost entirely be accounted for by a reduction in the number of submovements in a cycle. The results are discussed in the view of the hypothesis that considers submovements to be the building blocks of a graphical movement.

[Directed cortico-cortical functional connectivity at the earlier stages of serial learning in adults and children of 7-8 years old].

The serial learning at its earlier stages that presumably involve working memory was studied in adults and children of 7-8 who were reproducing a sequences of discrete movements following the order given by a sequence of visual stimuli. In both age groups, the learning curves (latent time vs. trial number) were qualitatively similar in shape. The overall shape of the learning curve depended on the relative share of fast vs. slow phases of latent time reduction. Comparison of cortico-cortical functional connectivity at the prestimulus period in the sequence reproduction task vs. the simple visuo-motor reaction task showed an overall tendency for an increase in influence of postcentral cortical areas accompanied by a reduction in influence exerted by the prefrontal and the central cortical areas. In particular, it was typical for adults to show an increase in directed influence of TPO cortical areas while in children, an increase of directed influence of parietal cortex was also observed. Comparing subgroups with different shapes of learning curves showed a difference in the directed functional connectivity in those subgroups. The results are discussed with a particular focus on the role of working memory retaining the internal representations of sequences being learned.

[Study of cortico-cortical functional connectivity with vector autoregressive model of multichannel EEG].

This review focuses on some practical issues of using vector autoregressive model (VAR) for multichannel EEG analysis. Those issues include: EEG preprocessing, checking if the necessary conditions of VAR model applicability are met, optimal order selection, and assessment of the validity of fitted VAR model. Both non-directed (ordinary coherence and imaginary part of the complex-valued coherency) and directed (directed coherence, directed transfer function and partial directed coherence) measures of the strength of inter-channel coupling are discussed. These measures are analyzed with respect to their properties (scale invariance) and known problems in using them (spurious interactions, volume conduction).

[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.

[Producing a sequence of movements in response to a sequence of visual stimuli. Inter-individual differences in early phase of sequence learning].

In this work, we studied the inter-individual variants at the early stage of serial learning in the sequence reproduction task where subjects were asked to produce a sequence of movements whose serial order was given by the sequence of visual stimuli. A total of 20 adults participated in the experiment where, besides the sequence reproduction task, each subject also performed the simple visuomotor reaction time task, the choice reaction time task and the serial reaction time task. It was found that individual latencies vs. trial number plots (learning curves) were characterized by one distinctive feature: the latency reduction, if any, took a form of either an abrupt decline down to a stationary level (fast phase) or a gradual approximately linear leveling off over the entire block of 60 trials (slow phase). The diversity of the individual learning curves were limited to the following four types: a flat curve, a curve with the fast phase only, a curve with the slow phase only, and a curve that combined both phases with the leading fast phase followed by the slow phase. All the subjects were subdivided into four groups according to the subject's type of learning curve. We analyzed the correlation pattern between temporal indices (latencies and inter-response intervals) and compared these indices to simple visuomotor reaction time, choice reaction time and the amount of learning in the serial reaction time task. The significant between-group differences found in this analysis suggest that there are some essential functional differences related to the group break up. It was suggested that inter-individual variants in the character of the early stage of sequence learning are determined mainly by the functional and structural complexity of the internal representation of the sequence and by the way the working memory operates in order to recognize the driving sequence of visual stimuli and to translate the internal representation of a sequence into motor commands.