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.     

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.     

Circadian rhythms in phonological and visuospatial storage components of working memory

Working memory is a basic cognitive process that temporarily maintains the information necessary for the performance of many complex tasks such as reading comprehension, learning and reasoning. Working memory includes two storage components: phonological and visuospatial, and a central executive control. The objective of this study was to identify possible circadian rhythms in phonological and visuospatial storage components of working memory using a constant routine protocol. Participants were eight female undergraduate students, aged 17.5±0.93, range = 16 - 19 years old. They were recorded in the laboratory in a constant routine protocol during 30 h. Rectal temperature was recorded every minute; subjective sleepiness and tiredness, as well as phonological and visuospatial working memory tasks, were assessed each hour. There were circadian variations in correct responses in phonological and visuospatial working memory tasks. Cross-correlation analysis showed a 1-h phase delay of the phonological storage component and a 3-h phase delay of the visuospatial storage component with respect to rectal temperature. This result may explain the changes in the performance of many complex tasks during the day.     

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.     

Factor analysis of interrelations between EEG waves with various frequency ranges in adults and 5-6 year old children]

Statistical interrelations among different amplitude-temporal features of the EEG waves of different frequency bands in adults and 5-6-year old children are determined mainly by two factors. The first one is related to the alpha-wave index and amplitude and the beta-wave index, the second one--to the alpha-wave average period. Adults revealed a higher level of negative correlation between the EEG wave amplitude and index and the theta-wave index than the 5-6-year old children.     

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.     

Interhemispheric differences in the spectral power and coherence of EEG rhythms in children with autism spectrum disorders

Electroencephalographic examination of boys aged 4–9 years with autism spectrum disorders (ASDs) showed spectral power values and coherence in high-frequency bands (20–60 Hz) in various brain areas were higher than normal. Differences in spectral power were greater in the anterior areas of the left hemisphere; differences in coherence, in the right anterior and posterior areas. Interhemispheric differences typical of healthy subjects were absent in the children with ASDs. The spectral power of the θ rhythm was lower in autism, especially in the left hemisphere. The spectral power of the α rhythm in the autistic children was lower than normal, especially in the posterior areas of the left hemisphere. The μ rhythm was higher than normal in spectral power and was localized in the right, rather than left, anterior areas. The children were examined again after corrective procedures. The α-rhythm spectral power increased (became closer to the norm) in the left posterior areas, while the γ-rhythm spectral power decreased (became closer to the norm) in the right anterior areas in some of the autistic children. The electrophysiological changes were associated with improved psychological testing results, especially in nonverbal measures.     

Lower and upper limb length of urban and rural 7-11 years old Turkish school children

This study was carried out on 779 male and 755 female 7-11 years old children, who are students of the primary schools in Diyarbakir city center and center connected areas. The average values of lower and upper extremity lengths of children in center and rural primary schools have been compared, and the results have been analyzed with the Student t-test. The relation between lower and upper extremity length averages and height is shown by correlation coefficients. It is observed that in the 11 years old boy's group and in the 9 years old girl's group of the center primary schools the total arm lengths are longer (p < 0.01). Upper and lower extremity lengths are increasing parallel to height. Iliospinal heights are obviously longer in the 11 year old group of boys and the 7, 9 and 11 year group of girls in the center primary school.     

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 θ, α₁, α₂, and β₁ 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.     

Early influences on blood pressure: a study of children aged 5-7 years.

OBJECTIVE--To examine factors that influence blood pressure in children. DESIGN--Cross sectional study of children aged 5.0-7.0 years who had blood pressure measurements and for whom parental questionnaires were completed. SETTING--School based survey. SUBJECTS--3591 Children aged 5.0-7.5 years selected by stratified random sampling of primary schools in nine British towns (response rate 72%); 3591 were examined and their parental questionnaires were completed. Data were complete for birth rank in 3559, maternal age in 3542, maternal history of hypertension in 3524, and paternal history in 2633. RESULTS--Birth weight was inversely related to mean systolic blood pressure but only when standardised for current weight (weight standardised regression coefficient -1.83 mm Hg/kg (95% confidence interval -1.31 to -2.35). Mean diastolic pressure was similarly related to birth weight. Maternal age, birth rank, and a parental history of hypertension were all related to blood pressure. After standardisation for current weight a 10 year increase in maternal age was associated with a 1.0 mm Hg (0.4 to 1.6) rise in systolic pressure; first born children had systolic blood pressure on average 2.53 mm Hg (0.81 to 4.25) higher than those whose birth rank was greater than or equal to 4; and a maternal history of hypertension was associated with a systolic pressure on average 0.96 mm Hg (0.41 to 1.51) higher than in those with no such history. The effects described were largely independent of one another and of age and social class. The relation for birth rank was, however, closely related to that for family size. CONCLUSIONS--Influences acting in early life may be important determinants of blood pressure in the first decade. The relation between birth weight and blood pressure may reflect the rate of weight gain in infancy. The reasons for the relation with birth rank and maternal age are unknown; if confirmed they imply that delayed motherhood and smaller family size may be associated with higher blood pressure in offspring.     

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 shortterm appearance of bilateral synchronous slow waves over the frontal and/or frontal and 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 frontal and 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.     

Evaluation and reproduction of time intervals in 7-10-year old children

We examined 200 children at the age of 7-10 (100 boys and 100 girls). The subjects had to estimate and reproduce time intervals in the range of 15-90 s. It was found that the children reproduced the intervals better and with lesser deviations than they estimated the intervals. The precision of time estimation increased with age and was best in ten-ear-old children. The findings confirm the authors' hypothesis about the "active" and "passive" time perception.