Structural and functional organization of a developing brain and formation of cognitive functions in child ontogeny

Results of multidisciplinary studies, including neuromorphological, neurophysiological, neuropsychological, and psychphysiological studies, are reviewed. They allow the brain mechanisms of cognition formation and development during maturation to be identified. The role of regulatory (modulatory) brain systems in forming the cognitive function in the child is demonstrated. Data on considerable changes in the brain systems responsible for the development of cognitive functions in children between the ages of five to six and seven to eight years are presented. At this age, the morphological and functional maturations of the frontal cortical areas and their descending connections with other cerebral structures increase the efficiencies of arbitrary selective attention, learning the activity program, inhibition of spontaneous responses, and regulation and organization of activity, i.e., the functions that are important for successful schooling.     

Continuity and prospects of research in systemic integrative psychophysiology of functional states and cognitive activity

An important problem of psychophysiology related to the study of the integration of the mechanisms controlling the state of the brain and characteristics of the cerebral organization of cognitive activity is discussed. The fundamental role of the results of long-term research in the neurophysiology of functional states as the basis of the organization of mental activity under conditions of direct, long-term, sparing contact with the cortex and subcortical structures by means of long-term intracerebral electrodes carried out by Academician Bechtereva and her scientific school is demonstrated. The commensurability and complementarity of slow and ultraslow gradual neurophysiological processes with similar amplitude-time parameters recorded in intravitally identified zones of deep cerebral structures and from scalp sites corresponding to the cortical projections of the main integrative centers are substantiated. The notion of the brain as a complexly organized, “floating,” multicircuit neurodynamic suprasystem with hierarchically, probabilistically organized vital processes varying in rate and intensity that are involved in maintaining the state of rest, mental states, and cognitive activity are formulated and substantiated. While the set of universal neurodynamic languages is limited, the brain employs a multiregister mechanism controlling the state and selective mechanisms of integration, ensuring the contribution of gradual neurophysiological processes at different levels of the structural and functional organization that vary in terms of information content in the formation of the cerebral systems underlying specific cognitive activities.     

Neurophysiological mechanisms of voluntary attention: a review

The review is focused on attention as behavior-controlling process. Neurophysiological, electrophysiological and neuropsychological studies of different brain structures during voluntary attention are analyzed. These data show that selective voluntary attention modulates activity of sensory specific cortical zones involved in relevant signal processing. Fronto-thalamic system consisting of prefrontal cortex and thalamic mediodorsal nuclei is shown to be main source of top-down selective modulation of voluntary attention. The review proposed the hypothetical model of selective cortical activity modulation during voluntary attention based upon the available data and evidence of own electroencephalographic studies.     

Features of the Brain Functional Organization in Right- and Left-Handed 6- to 7-Year-Old Children during Visuospatial Performance of Different Complexity: II. Analysis of EEG Parameters during Complex Visuospatial Performance

The features of brain functional organization during complex visuospatial performance were studied in 6- to 7-year-old right- and left-handed children. Differences in the brain functional organization were revealed between children with different profiles of manual asymmetry. Presentation of complex experimental tasks to right-handed children resulted in the formation of selective functional connections between centers, which is indicative of the use of economical and efficient mechanisms of the organization of activity. Generalized functional integration was observed in left-handed children, which reflected an immature type of regulation of cortical activity.     

Brain Mechanisms of Voluntary Regulation of Activity during Acquisition of the Skill of Writing in Seven- to Eight-Year-Old Children

With the aim of studying the formation of brain mechanisms of voluntary activity regulation in junior schoolchildren and the role of these mechanisms in the acquisition of the skill of writing, a complex neuropsychological investigation was carried out. In the EEG of children with learning problems and a deficit of voluntary activity regulation (VAR), signs of the functional immaturity of the fronto–thalamic regulatory system (FTS) were found. Comparative neuropsychological analysis revealed a specific impairment of the VAR in these children in the form of pronounced impulsiveness, instability of a program, problems in switching over from one program to another, and self-control difficulties. It is concluded that the functional maturation of the FTS is a mechanism of VAR development. It is shown that the VAR deficiency in children with FTS immaturity is combined with a delay in the development of semantic and mediating speech functions. It was found that the features of the development of the higher mental functions in seven- to eight-year-old children with FTS immaturity specifically affect both the semantic and graphic aspects of writing acquisition.     

Peculiarities of formation of the cognitive functions in junior school children with different maturity of regulatory brain systems

To reveal the specific role of maturation of modulating, regulatory brain systems in formation of cognitive processes at the junior school age, was performed a complex electroencephalographic and neuropsychological examination of the 7–8-year-old children with different degrees of functional maturity of the regulatory systems. It has been shown that an essential factor determining formation of the higher psychic functions (HPF) at the junior school age is maturation of the fronto-thalamic system. Immaturity of this system in the 7–8-year-old children leads to a deficiency of functions of programming, regulation, and control of the activity. The most substantial changes were revealed for the components of the voluntary organization of the activity, which are connected with its selectivity both in realization of current tasks and in creation of the activity strategy. The deficiency of processes of voluntary regulation in the 7–8-year-old children with immaturity of the fronto-thalamic system is combined with a delay of development of the meaning-forming speech function. Comparison of data of the neuropsychological and electroencephalographic examination has permitted suggesting that the basis of the revealed changes in the HPF formation in the 7–8-year-old children is immaturity of the main neurophysiological mechanisms that provide a selective involvement of different cortical regions in providing their activity both in the course of its realization and during preparation to it as well as an under-development of differentiated intracortical connections in the left hemisphere.Translated from Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, Vol. 40, No. 5, 2004, pp. 427–435.Original Russian Text Copyright © 2004 by Machinskaya, Semenova.To the 100-Anniversary of N. N. Traugott     

The Role of the Genotype in the Development of the Neurophysiological Mechanisms Involved in the Spatial Integration of Neocortex Bioelectric Activity

The contribution of genetic factors into the formation of the neurophysiological mechanisms determining the systemic organization of cortical activity has been estimated in 12 pairs of monozygotic (MZ) and 5 pairs of dizygotic (DZ) twins (18–25 years of age). The similarity of individual patterns of the spatial interaction of cortical bioelectric activity measured for different combinations of EEG statistical relationships from 16 monopolar leads has been estimated in each pair of twins and in each of the 544 pairs of unrelated subjects in both groups. The results of the study suggest a high population invariance and small genetic and phenotypic variations of the morphofunctional systems constituting the main neurophysiological mechanisms of general cerebral integration. Brainstem and subcortical regulatory structures play the leading role in the integration of different brain regions into an organized system. Apparently, the formation of these structures during ontogeny follows the same general pattern in all individuals, because deviation from it is likely to affect the fundamental monomorphic characters of the species. The formation of neocortical interregional connections may be expected to exhibit greater individual variation, with the roles of hereditary and environmental factors in the formation of long and relatively short intercortical interactions being different. Apparently, the individual variation of the long intra- and interhemispheric fiber pathways forming the specific morphological framework of the neocortex is largely determined by the genotype. However, the intercentral interactions mediated by short corticocortical connections that are formed in the course of the vital activity of an individual are likely to be mainly determined by the external and internal environments.     

Continuity and prospects of development of researches in area system-integrativity of psychophysiology of functional state and cognitive activity

In the review one of actual problems of psychophysiology in studying a phenomenon of integration of mechanisms of regulation of state of a brain and features of the organization is discussed by a brain of cognitive activity. Basic value of results of long-term researches of academician N.P. Bechterevoj and of her school is opened in the field of neurophysiology of functional states as bases of the organization of mental activity in conditions of direct, long and sparing contact to a cortical and subcortical structures of a brain, with the help long-term intracerebral electrodes. Arguments about a commensurability and complementary value similar on amplitud-time parameters slow and superslow gradual changes of neurophysiological processes registered simultaneously in identified zones of subcortical structures of a brain and with removal from a surface of a head in cortical projections of basic integrativity of the centres are submitted. Representations about a brain as difficultly organized "swimming" many-contour, neurodinamic informational-controlling suprasystem with hierarchically, probability a principle of the organization different on speeds and intensity of processes of the ability to live participating in maintenance of a condition of rest, mental conditions and cognitive activity are formulated and argued. At the limited set universal neurodinamic "languages", the brain has the multiregister mechanism of regulation of conditions and selectivity of mechanisms of the integration providing the contribution differing on information maintenance gradual neurophysiological of processes of different levels of the structurally functional organization in formation of brain systems of maintenance of concrete kinds of cognitive activity.     

Organization of Regional Interactions of the Brain Cortical Activity during the Common-root Word Derivation Task

This study analyzed specificities in the activity of the neurophysiological mechanisms underlying the organization of active word-derivation processes. The regularities in the reorganization of the spatial structure for the systemic interaction of bioelectrical activity between different cortical areas of the cerebral hemispheres were studied in adult subjects during the test for mental derivation of common root words (i.е., using the modern methods of the so-called “functional connectome” investigations). Сross-correlation and coherent analysis of EEG has shown that the ipsilateral statistical EEG interactions in the left hemisphere, including Broca’s and Wernicke’s areas, were significantly increased in adults during mental derivation of common root words and, simultaneously, the interhemispheric connectivity and the EEG interactions in the right hemisphere were reduced. Comparison of our results with the previous data of verbal activity associated with speech perception and production has revealed significant differences in the degree of involvement of the left and right hemisphere cortical activity in verbal processing. For example, unlike the data of current study, an equal involvement of both hemispheres cortical activity was recorded during the phoneme recognition in auditory perceived words, grammatical and semantic errors in sentences, as well as during mental formation of words from a set of phonemes and sentences from a set of words, which was particularly manifested in the increased of hemispheric interactions, predominantly, in the inferior frontal and temporal areas and the overlapped areas of the temporal, parietal, and occipital cortical zones (TPO) of both hemispheres. Thus, the data obtained in this study indicate the presence of expressed specificities in the lateralization of activity in the neurophysiological mechanisms underlying the processes of active word derivation and inflexion.     

Neurophysiologic mechanisms of attention disorder in children with learning difficulties

In order to study neurophysiological mechanisms of the disturbance of voluntary attention in children of 6.5-9 years old, which had difficulties in learning caused by a delay of psychic development (DPD), characteristics were studied of electrocortical and vegetative components of orienting reaction (OR) to indifferent and relevant stimuli and also of background EEG. A decrease of OR components revealed in situation of involuntary attention against the background of insufficiently formed cortical rhythm of alpha-range, as compared with the norm, is compensated at the increase of stimuli significance by verbal instruction. These facts confirm the supposition about deficit of regulating influences of the frontal cortical areas on the ascending activating system in children with difficulties in learning. Deficiency of the involvement of the central cortical areas in OR realization, typical of the children with DPD in a situation of voluntary directed attention, can be considered as reflection of disturbances of integrative brain activity.     

Functional organization of the brain in the period of preparation for recognizing fragmented images in seven- to eight-year-old children and adults

Functional connectivity between the prefrontal cortex and the temporal and temporo-parieto-occipital cortices in the process of preparing for the recognition of fragmented images were analyzed in adults (n = 26) and seven- to eight-year-old children (n = 20).The evaluations of the imaginary part of the complex-valued coherency for the EEG alpha-rhythm (Jα) were used as an index for the strength of cortico-cortical interactions. The Jα value was analyzed in the following three experimental conditions corresponding to different stages of readiness for visual recognition: (1) nonspecific attention holding in the period preceding a warning stimulus (S1); (2) focused attention in the interval preceding a not-yet-recognized target stimulus (S2) and (3) pretuning preceding a recognized stimulus (S3). Adult subjects tended towards a growing level of functional connectivity in α-rhythm in progressing from attention holding to focused attention preceding the emergence of a target stimulus, but children, on the contrary, demonstrated a decreasing trend. Comparing the Jα values in the subgroups of adults and children who showed the highest recognition scores in the solution of cognitive tasks helped reveal age-specific patterns in the rearrangements of cortico-cortical functional connectivity in α-rhythm in the left and right hemispheres at different stages of readiness for recognizing incomplete images. In adults, the maximal Jα values were found in the left hemisphere in the interval preceding the recognition of a target image. At this stage of pretuning, the Jα values at the leads in the left hemisphere in adults significantly exceeded those in children. The Jα values for the right hemisphere in adults were maximal during focused prestimulus attention when the image was not yet recognized and these values were significantly higher than in children under the same experimental conditions. Children showed maximal Jα values in both hemispheres during nonspecific attention. The specifics of functional connectivity observed between the prefrontal, temporal and temporo-parieto-occipital cortices in seven- to eight-year-old children during functional pretuning to the recognition of fragmented images are considered to reflect the relative immaturity of neurophysiological mechanisms underlying the voluntary attention and working memory in children of this age group.     

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.     

Voluntary regulation of the functional state and its influence on the effectiveness of cognitive activity during adolescence

We have analyzed the impact of voluntary relaxation on the functional organization and the effectiveness of the voluntary prestimulus attention in performing cognitive tasks in adolescents at the ages of 12–13 and 13–14 years. The effectiveness of cognitive task performance (audio-verbal short-term memory) was estimated on the basis of the number of correctly remembered words. We have found that both age groups are characterized by reduced capacity for voluntary relaxation and its impact on the effectiveness of cognitive task performance. The analysis of the coherence function of EEG rhythmic components in a situation of voluntary attention focused on the performance of cognitive tasks showed no significant change in the interaction of the prefrontal cortex with other cortical areas during the switch from quiet wakefulness or post-relaxation state to the preparation to perform the task, which is typical of adults and young children. Our findings can be a result of sub-optimal functioning of voluntary regulation mechanisms and organization of activities during adolescence.     

Formation of the functional organization of the cerebral cortex at rest in young schoolchildren varying in the maturity of cerebral regulatory systems: II. Analysis of EEG α-rhythm coherence

Coherence (COH) of rhythmic components of the EEG α rhythm at rest was analyzed to demonstrate that the maturation of deep regulatory systems (RSs) of the brain at different levels substantially affected the functional organization of the cerebral cortex and the time course of the formation of intercentral connections in young schoolchildren. The specific effect of fronto-thalamic regulatory system immaturity (FRSI) was a decrease in the α-rhythm COH predominantly in neighboring left-hemispheric derivations of foci in the anterior temporal area. A deficit of nonspecific activation had the strongest effect on the α-rhythm integration of right-hemispheric areas, although this effect was less distinct than that of FRSI and remained only as a tendency by the age of nine to ten years. Children with normal and functionally immature cerebral RSs differed from each other with respect to age-related changes in the corticocortical connections, especially in the left hemisphere. In the norm, intense growth of functional connections in the left hemisphere ceased in the period between seven to eight and nine to ten years of age; in contrast, children with RS immaturity exhibited a trend towards an increasingly greater amount of these connections in both hemispheres, which, apparently, corresponded to an earlier stage of ontogeny.     

Manifestations of selective visual attention in human parietal and temporal cortex according to evoked potentials

The event-related potentials (ERPs) in visual discrimination task in parietal and temporal cortical areas were recorded in 11 young adults during passive observation (involuntary attention) and target selection (voluntary attention). The voluntary selective attention resulted in: 1) increased ERP correlation between the parietal; and temporal cortical areas; 2) increased correlation of sequential ERPs in monopolar leads (P3, P4, T3, T4, T5, T6); and 3) increased correlation of sequential ERPs in bipolar leads (P3-T3, P3-T5, P4-T4, P4-T6). The findings suggest that voluntary attention maintains a concordant activity of the parietal and temporal cortical areas in execution of visual selection tasks.     

A comparative electrophysiological study of regulatory components of working memory in adults and seven- to eight-year-old children: An analysis of coherence of EEG rhythms

Coherence at the frequency of θ, α, and β 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 (reference) 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 θ-related functional coupling between medial areas of the frontal cortex and temporal cortical zones and by a strengthening of local β-related functional connectivity in the fronto-central areas of the cortex. In children, no such increase was found for θ rhythm; for β 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 α coherence in distant fronto-parietal links, predominantly in the right hemisphere, while in children information retention was accompanied by the growth of θ 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.     

Functional organization of the cortex of the large hemispheres during voluntary movement performance: Age aspect

The method of estimation of the coherence (Coh) function values of EEG rhythmic components disclosed the specific features of functional associations of cortical regions during the performance of voluntary graphic cyclic movements under usual and unusual conditions. A significant increase in the Coh function values of the α-rhythm was observed both in the contralateral hemisphere and the symmetrical central and parietal cortical regions in adult subjects during right-hand movement performance with open eyes (usual conditions); in this case the resulting functional associations included motor zone and cortical regions responsible for visual information analysis and perception. During right- and left-hand movement performance with closed eyes (unusual conditions), the mature-type functional organization had a bilateral character with interrelated activity focused in the frontal regions that clearly demonstrated the function of these structures during formation of new motor programs. The significant changes in cortical mechanisms of voluntary graphic movements were disclosed in young 7- to 8- and 9- to 10-year-old schoolchildren.     

EEG Spectral Characteristics in Junior Schoolchildren with Learning Problems

EEG spectral characteristics were studied in two age groups (7–8.5 and 8.5–10 years) of mentally healthy children and children with learning problems at rest and during performance of a Raven test. It was shown that slow frequencies are more pronounced in the EEG of 7- to 8.5-year-old children with learning problems than in EEG of healthy children of the same age group. An immature form of EEG activation, i.e., an increase not only in the but also in the frequencies during activity, was characteristic of these children. The reaction of the activation of the definitive type develops between the 8.5–10 years of age. This reaction is correlated with an increase in the efficiency of the sensory perceptive and sensorimotor activity. The distinctive feature of children with learning problems between 8.5–10 years of age is a greater expression of slow frequencies in the baseline EEG of the frontal (in particular, left frontal) areas of the cortex. The obtained results are considered as a reflection of a retardation of the functional maturation of the brain structures responsible for the deficit of involuntary and voluntary attention and the disorder of a systemic organization of perception and analytical–synthetic brain activity as compared to the normal age characteristics. Possible neurophysiological mechanisms responsible for learning problems in junior schoolchildren are discussed on the basis of the obtained results and evidence from the literature.     

The interaction of perception and attention at different stages in individual development

In the study carried out on children aged 10 years (51 persons), subjects aged 16-17 (11) and adults (19) characteristics of the perception and attention interaction were studied by means of electrophysiological parameters analysis (ERP, CNV, EEG) of the process of solution of various visual tasks. It has been shown that adequate brain provision of this process is based in adults both on the functional topographic differentiation and specialization of separate perceptive operations and on the possibility of controlling generalized and local activating influences according to task requirements. In children aged 10, not differing from the adults by the success of the perceptive activity, age peculiarities of its strategy are revealed connected with functional brain organization. Basic distinctive features of children perceptive activity are intensified regional specificity manifested both in responses to relevant and non-relevant stimuli, and excessive generalized activation testifying to incomplete structural-functional maturation of the frontal regions of the cerebral cortex. Increasing functional activity of these structures in ontogenesis provides for the selectivity of perceptive, cognitive and activating processes, adequate to the requirements of the task.     

Formation of the functional organization of the cerebral cortex at rest in young schoolchildren varying in the maturity of cerebral regulatory systems: I. Analysis of EEG spectral characteristics in the state of rest

Spectral correlation analysis of the EEG was used to study the organization of the rhythmic electrical activity (EA) of the cerebral cortex in normal children aged seven to eight and nine to ten years and children with the two types of functional immaturity of cerebral regulatory systems most common at this age, namely, fronto-thalamic regulatory system immaturity (IFTS) and brainstem nonspecific activation system immaturity (deficiency) (DNA). Statistical comparison (ANOVA) of these groups of children with respect to the absolute and relative α-and ?-band spectral powers of the background EEGs of 12 cortical areas showed the specific features of the effects of functional immaturity of regulatory systems at different levels on the cortical rhythmic EA pattern at rest. DNA led to a significant increase in the absolute spectral power of α and ? waves recorded in all derivations in both age groups, which indicated a generalized decrease in cortex activation in these children. IFTS caused a significant decrease in the relative strength of α waves and an increase in the strength of ? waves. Taking into account the results of ontogenetic studies, this may be regarded as evidence for a relative underdevelopment of cortical rhythm-generating networks. The absolute spectral powers of both α and ? waves were decreased in all groups of children by nine to ten years of age, which indicated that nonspecific activation was enhanced in the age interval studied. Significant changes were observed in children with functional immaturity of regulatory systems. In children with DNA, the age-related increase in cortex activation was expressed as a significant increase in the α-rhythm peak frequency. In children with IFTS, by nine to ten years of age, both the absolute and relative strengths of ? waves were decreased in most cortical areas studied, which may be regarded as the progressive formation of cortical rhythm-generating mechanisms.