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.     

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.     

Peculiarities of EEG in hard-of-hearing children of primary school age

Electroencephalographic examination of 7-to 9-year-old children with sensorineural deafness of degrees II and III included EEG recording in the resting state, in the course of reaction of activation (at opening of the eyes), under conditions of rhythmic photostimulation with frequencies of 4, 6, 9, and 12 sec⁻¹ and under those of the hyperventilation test. The results allow us to conclude that systems responsible for generation of EEG in hard-of-hearing children demonstrate some functionally immaturity. The following facts confirm the above conclusion. As compared with the norm, greater normalized spectral powers (SPs) of the delta and theta rhythms, a higher intensity of electrogenesis (integral power of oscillations) within all frequency ranges, and a smaller mean frequency of the dominant rhythm were typical of hard-of-hearing children. In these children, the reaction of activation in the majority of cases looked like incomplete suppression of the alpha rhythm. Upon rhythmic photostimulation, hard-of-hearing boys and girls demonstrated following of the rhythm at frequencies of 4 and 6 sec⁻¹ while children with normal hearing demonstrated that at 9 and 12 sec⁻¹ frequencies. The characteristics of EEG reactions under the conditions of the hyperventilation test reflected the immaturity of the fronto-thalamic controlling system, as well as certain dysfunction of lower brainstem regions in children with disorders of hearing. Neirofiziologiya/Neurophysiology, Vol. 40, No. 2, pp. 137–146, March–April, 2008.     

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.     

Characteristics of visual perception in seven-year-old children differing in functional maturity of brain structures

Individual and age-related characteristics of visual perception as a whole and its individual components were studied in seven-year-old children as related to their brain functional development. A dependence was found between the success of visual perception and the characteristics determining the functional maturity of both the cerebral cortex and the brain regulatory structures. Difficulties in noise resistance, visuospatial perception, and visual analysis/synthesis were greater in first-year school students with signs of immaturity of the bioelectrical activity of the cerebral cortex. Poor development of the visual perception system in schoolchildren was also determined by an underdeveloped frontothalamic regulatory system and deviations in the functional state of the nonspecific activation system.     

The role of damage to the cerebral subcortical divisions in the formation of alalia

The role of the cerebral subcortical structures in speech formation was studied by analyzing the data on the comprehensive examination of children with alalia. Alalia is a systemic underdevelopment of speech in which all the speech components are disordered. The assessment of the functional state of the brain structures by means of EEG allowed us to identify two groups differing in the pattern of changes in bioelectrical activity (BEA): group 1 with α rhythm changes and/or local BEA changes, predominantly in the left hemisphere, and group 2 with predominantly generalized EEG changes of brainstem origin. Integrated analysis of clinical data allowed us to suggest that a lesion of the left hemisphere subcortical structures and the brainstem divisions underlies the formation of alalia. The analysis of the perinatal risk factors allowed us to advance the hypothesis that damage to the subcortical structures was linked to antenatal complications in the first half of pregnancy.     

Psychophysiological and neurophysiological features of the organization of visuo-spatial performance in right-handed and left-handed six- to seven-year-old children

The developmental features of individual components of the visual perception and brain functional organization during visuo-spatial activity of different complexity were studied in right-handed and left-handed 6–7-year-old children. The results of psychophysiological testing of their visual perception testify to the underdevelopment of the mechanisms of integrative brain activity. Some specific features of the brain functional organization were revealed in the left-handed children during visuo-spatial performance. More autonomous functioning of the cerebral hemispheres and the duplication of the activation processes in the right and left hemisphere during visuo-spaital performance of different complexity are characteristic of these children. This is probably associated with the involvement of compensatory mechanisms, which enable the performance reliability.     

The concept of typological variability of physiological individuality: III. Psychophysiological characteristics of functional types differing in habitual physical activity

Results of longitudinal studies were used to estimate the psychophysiological characteristics of preschool and young school children and young adults of both sexes belonging to functional types (FTs) with low, medium, and high habitual physical activity (HPA) levels (FT-1, LHPA; FT-2, MHPA, and FT-3, HHPA, respectively). Statistical analysis of the distributions of averaged psychophysiological parameters in the total sample with the use of the χ² and λ tests showed wide quantitative and qualitative ranges of psychophysiological individuality in a healthy population and demonstrated that it is reasonable to distinguish three typological groups (FT-1, FT-2, and FT-3). Typical first- and second-order parameters, as well as the results of third-order tests characterizing the current state, were determined for each FT. Determination of the psychophysiological characteristics of FT-1, FT-2, and FT-3 and their prevailing behavioral tendencies makes it possible to differentiate between strategies of organism-environment interaction and estimate their advantages and disadvantages.     

Efficiency of biofeedback training of functional state regulation depending on individual psychophysiological characteristics

The psychophysiological characteristics of the subjects (emotional stability, autonomic lability, tension of autonomic regulation of cardiac activity, and EEG characteristics) were estimated. The efficiency of relaxation regulation training with the use of biofeedback (with the electrocutaneous impedance as a BF signal) was studied. Before and after BF training, an electrophysiological experiment was carried out, namely, a “relaxation test” without BF support. The test consisted of three situations: background, relaxation, and the state after coming out of relaxation. During the test, EEGs of different cortical areas (α bands) and autonomic indices were recorded. A short-term memory test was carried out with the purpose of controlling changes in the functional status. It has been shown that even a short training cycle of five sessions in most cases provided relaxation and improvement in self-regulation, accompanied by improvement of the mnestic activity. The effect of individual psychophysiological characteristics on the success of BF training has been established. A high autonomic lability, a high level of nonspecific cortex activity, as well as a dysfunction of the frontal-thalamic system, should be regarded as factors preventing effective self-regulation training.     

Cluster structure of the psychomotor and coordination spheres in younger schoolchildren

The goal of this study was to describe typical motor profiles in younger schoolchildren. A total of 89 subjects aged 8–10 years, students of primary schools of Moscow not going in for sports took part in the study. Twenty-five indices of psychophysiological (NS-PsihoTest), psychomotor (KID-3), posturography and locomotor tests (nine coordination tests) have been measured. According to their motor coordination, the children have been subdivided into groups using k-means cluster analysis. The four obtained clusters are supposed to reflect different types of motor coordination and correspond to four individual motor profiles typical of children aged 8–10 years. These motor coordination types were not associated with age, sex, or constitution; therefore, they may be promising for selecting sports. The ability to anticipate and a high speed of wrist movement were typical of children from the first cluster. Subjects from the second cluster were more successful in rapid, rhythmic, and automatic actions, based on the mechanism of intrinsic programming. Subjects from the third cluster displayed a moderate ability of postural control, but at the same time, they were characterized by smooth, accurate, and rhythmic arm actions based on visual feedback, and an advanced sense of rhythm and space sense. Subjects from the fourth cluster were the most coordinated ones, which is important for sports and occupational activities requiring a high level of coordination.     

The state of the cardiovascular system in children aged 8–9 in the norm and in impairments of intellectual development

The specific features of the psychophysiological regulation of the cardiovascular system in healthy 8-to 9-year-old children and in children of the same age with impairments of intellectual development are considered. An analysis of the functional heart rhythm values after mental and physical exercise is given. The directions of correctional influence on the mechanisms of functional optimization of the cardiovascular system are outlined.     

The Functional State of the Cortex and Brainstem Regulatory Structures in Children with Speech Development Disorders

EEG recordings of 4- to 12-year-old children with general speech underdevelopment, dysgraphia, dyslexia, and sensorimotor and motor alalia were examined. EEG structural analysis improved the understanding of the neurophysiological mechanisms of these disorders. In most subjects, the left hemisphere was involved more than the right one. All groups were characterized by dysfunction or functional immaturity of the frontothalamic regulatory system or nonspecific activation deficiency. When dysfunction of brainstem regulatory structures was combined with impaired cortical rhythmogenesis, which reflects the functional immaturity of the cortex, this aggravated the defect and impeded corrective pedagogical measures.     

Electrophysiological and neuropsychological studies of the functional maturity of the brain cortex in first-graders with different levels of memory development

Visual analysis of the resting EEG revealed features of functional immaturity of cortical rhythmogenesis in a group of children with low parameters of memory. The closest correlations were observed between the neuropsychological parameters of memory and the character of the α rhythm, which confirmed the involvement of α oscillations in neurophysiological mechanisms of mnestic activity.     

Effect of Individual Features of the CNS on Efficiency of Relaxation Biofeedback Training in 9- to 10-Year-Old Children

The possibilities of biofeedback training for improvement of the self-control of the functional state (relaxation) were studied in 9- to 10–year-old children. At the first stage, under conditions of electrophysiological experiment, relaxation shifts were assessed in the cycle quiet wakefulness–relaxation–recovery of the initial state by autonomic (skin resistance) and EEG (spectra and coherence) indices. The children were then trained to control their functional state with a computer game including a feedback loop by skin temperature. After the training cycle, children were repeatedly examined in electrophysiological experiment with the instruction to control their state. Comparative analysis of self-induced relaxation changes before and after a successful training course revealed greater shifts of skin resistance and an increase in the number of distant functional connections (especially, in the intermediate and high-frequency EEG subbands), with a significantly increased coherence level during relaxation. A correlation was found between the efficiency of self-regulation training and some individual psychophysiological characteristics (simple motor reaction time, autonomic coefficient, resting EEG). Low efficiency of self-control training was observed in younger schoolchildren with a sharply deviant (from the mean group values) reaction time and autonomic coefficient, as well as with EEG manifestations of functional immaturity of the upper brain regulatory structures. The dependence of the EEG changes on the self-regulation strategy is discussed on the basis of obtained evidence and data in the literature.     

Structural Transformations of the Associative Cortex As the Morphological Base of the Development of Human Cognitive Functions from Birth to 20 Years of Age

The microstructure of the temporo-parieto-occipital subregion and the frontal area of the brain from birth to 20 years of age was studied using computer morphometry. These brain zones are involved in the higher integrative mechanisms of cognitive functioning in children, adolescents and young adults. Structural transformations of the cortex represent a stage-by-stage process. Each stage in the frontal and occipital associative zones has specific temporal limits and is characterized by the quantitative and qualitative specificity of the morphological changes at each of the system levels considered: neuronal, modular, and stratification. The structural modifications from birth to early adulthood are primarily associated with the final development of micro and macroassembles and their structural components, primarily, neurons of various types. The growth and differentiation of neurons involves heterochrony with respect to the terms and developmental rates in the frontal and occipital associative cortex. The terms of the most active synchronous postnatal structural modifications, occurring during the first year of life, during the years 2–3, 6–7, 9–10, and 13–14 were analyzed. It was shown, that local specialization of cellular ensembles at various levels is a consequence of the functional specialization of microensembles, involved in cortical information processing, including cognitive activity and other higher psychophysiological functions of the human brain.     

Quantification of Superoxide Radical in the Brain of Rats with Experimentally Induced Obstructive Jaundice

The study aimed to directly measure in vivo superoxide radical (O₂⁻) a direct indicator of oxidative stress, in the brain of rats with experimentally induced obstructive jaundice by employing a new quantitative ultrasensitive fluorescent assay requiring minimum sample. O₂⁻ anion is specific for dihydroethidine (DHE) and upon reaction gives a characteristic product, namely 2-OH-ethidium. Ten male rats underwent laparotomy and were divided into two groups: I, sham operated and II bile duct ligation. Ten days later, following injection with DHE (a O₂⁻ trap), all animals were killed and samples from cerebral cortex, midbrain and cerebellum were removed for analysis. It was shown that compared to group I, in group II the O₂⁻ was increased by 67% in the cerebral cortex and by 37% in the midbrain as a consequence of experimental obstructive jaundice, while its levels were unaffected in the cerebellum. The data in this experimental obstructive jaundice model imply a region-specific increase of O₂⁻ formation rate, being higher in cerebral cortex, less so in the midbrain and not at all in cerebellum.     

Atypical Forms of Cerebral α-Activity in the Case of Lesions in Regulatory Structures of the Human Brain

The results of the EEG study of patients with tumor lesion of diencephalic (29 subjects) and limbic (25 subjects) structures with the focus on the analysis of structural and functional organization of α activity have been summarized. It has been found that diencephalic structure dysfunction is accompanied by disorder of α-rhythm spatial organization in the form of generalization or translocation of its focus to the frontal regions of the cerebral cortex. Distinctive features of “diencephalic” type alteration of α rhythm are determined by predominant integration of the thalamic or hypothalamic structures into the pathological process. Involvement of the limbic structures, especially at early stages of the disease, induces increase in α-rhythm intensity in the temporal region of the affected hemisphere. The nature of the response of the EEG pattern to the functional stress allows identifying it as a “hippocampal α rhythm”. Implementation of the automatic methods of analyzing plays an important role in the identification of these specified pathologic forms of the α rhythm that are often invisible during visual assessment. Detected atypical forms of α rhythm facilitates the interpretation of hemispheric asymmetry of the EEG in patients with cerebral pathology.     

Age- and sex-related characteristics and mechanisms of adaptations during the prepubertal and pubertal periods of development

Integrated study of the functional state of the sympathoadrenal system and the adrenal cortex in children of both sexes aged 10–15 years. The study was conducted on the basis of the daily adrenaline, noradrenaline, 17-ketosteroid, and 17-oxycorticosteroid excretion values, which allowed certain synchrony to be established in the manifestation of the activity of the transmitter link of the sympathoadrenal system and the adrenal cortex androgenic and glucocorticoid functions with age, during sexual maturation. The heterogeneous character of maturation was found in the sex groups: in girls at an age of 10 and 12 years and in the boys at an age of 14–15 years. Changes in the excretion of the hormones and hormone metabolites with different directions and rates in the age-sex groups were observed throughout the academic year. In 14- to 15-year-old boys, a sharp increase in the daily excretion of the glucocorticoid metabolites accompanied by a substantial decrease in the age-related noradrenaline excretion values and the sex hormone metabolite values at an age of 15 years was observed. In the girls, these values varied within the age range, which indicates a more perfect character of the neuroendocrine regulation of their physiological functions in the period of sexual maturation.     

Functional coupling of cortical areas during problem-solving task: Analysis of θ rhythm coherence

The coherence of the components of the EEG θ rhythm was analyzed in subjects performing a visual object classification task under the conditions of uncertainty after a feedback. The functional coupling between cortical areas in the course of strategy formation was demonstrated to be stronger than at the stage when the strategy had already been formed. The θ-related functional connectivity were characterized by a specific topographic pattern: they converged to the foci located in the polar frontal cortex and reflect the interaction of these frontal areas with the anterior associative and temporal cortices of the left hemisphere, as well the parietal and occipital areas of both hemispheres. The frequency and topographic characteristics of the functional cortical links suggest that they reflect the functioning of a distributed neural network through which the limbic structures and the controlling frontal cortical structures interact in the process of cognitive strategy formation.     

Ontogenetic correlations between noradrenaline level and the density of adrenergic receptors in the rat brain

We studied the level of noradrenaline and the density of α2-and β-adrenoreceptors in the brain stem and cerebral cortex of 12-day- and 21-day-old rat fetuses, as well as of rats at the ages of 1, 2, 5, 7, 9, 16, 21, 35, and 70 days. We found a positive correlation between the level of noradrenaline in the brain stem and the density of β-receptors in the cerebral cortex, and between the amount of α2- and β-receptors in the cerebral cortex, as well as between the values of each of these indices of the neurochemical system and body weight. Significant negative correlations (r=−0.72 andr=−0.88, respectively) were found between the amount of α2-adrenoreceptors in the brain stem and the content of noradrenaline in this brain region, as well as in the cerebral cortex. Explanations of these positive and negative correlations between the level of noradrenaline and the amount of adrenergic receptors in the rat brain during ontogenesis are discussed.