V. P. Rozhkov

Interregional cortical interactions at different stages of natural sleep and the hypnotic state: EEG evidence

The characteristic patterns of EEG spatial organization at different stages of natural sleep and the hypnotic state were studied in 26 volunteers aged 18–22 years. EEGs were recorded using 12 monopolar leads, and EEG cross-correlation coefficient matrices were calculated for consecutive epochs (4 and 8 s). Matrices averaged for each state were treated using factor analysis. The EEG correlation matrices were compared element by element for the states studied and the waking state. Relatively similar changes in the spatial structure of EEG correlations were observed at different stages of natural sleep, with the correlations tending to intensify, especially in the posterior temporal region of the right hemisphere. In the light and deep (somnambular) phases of hypnosis, the interaction between cortical zones that was characteristic of distant relationships of the EEGs of frontal regions, especially the posterior inferior frontal region of the right hemisphere, decreased. The systemic reorganization of the interregional EEG correlations during natural sleep was considerably more pronounced than in the hypnotic state. Notwithstanding, the highly orderly spatial organization of the cortical biopotential field that was typical of the waking state was retained at different stages of natural sleep and hypnosis. Thus, the coordination of the activities of distant nerve centers oriented to providing for a certain function or maintaining a certain functional state occurs against the background of a relatively invariant pattern of interregional integration at the level of the whole brain.

Psychophysiological and cardiohemodynamic effects of solar, geomagnetic, and meteorological factors in humans under the conditions of the arctic region

The influence of variations in solar, geophysical, and meteorological factors, as well as of the lunar cycle phases, on cardiohemodynamic, emotional and CNS parameters has been studied in 12 men (19–38 years old) permanently residing in the Arctic region (the town of Apatity, 67°57′ N, 33°39′ E). The period of observation was characterized by M1 and M2 class solar flares and G1-G3 class geomagnetic storms. The study has demonstrated the adaptive modulation effects of environmental factors on autonomic regulation systems and the perturbing influences of geomagnetic storm and solar chromospheric flares on human functional state. Multiple regression analysis was used to identify the dominant environment factors by the degree of their influence on functional parameters and to assess their combined effect. The coefficient of determination was no more than 0.5 on average; however, in some subjects, it reached 0.7–0.8 for certain parameters. All subjects were shown to respond to the permanent fluctuations of climatic-geographical and cosmophysical factors under the extreme conditions of high latitudes; however, response pattern and intensity depended on individual sensitivity to their isolated and combined effects.

Formation of the Interaction between the Wave Components of the Main EEG Rhythms in Children up to Five Years of Age

Using the analysis of the interaction between EEG components [1], the authors studied the regularities of the formation of the EEG wave structure in 36 children aged 4 to 7 months, 2 to 3 years, and 4 to 5 years. The EEG of 4- to 7-month-old children had a relatively organized temporal structure, whose components were connected mainly with those of the slow-wave range. This structure is reproduced in most of the leads and is more stable in the anterior cortical areas than in the posterior ones. The waking 2- to 5-year-old children had two “functional” nuclei in the relation structure of the EEG components characterized by statistically significant enhancement in the probability of the consecutive appearance of waves of certain ranges. These nuclei include a slow-wave nucleus in the range of the Δ2–θ1-frequencies and an “alpha”-nucleus in the α1- and α2-ranges (θ2 and α1 2- to 3-year-old children) of the EEG frequencies. The relations between the components of the slow-wave nucleus begin to form in infants, prevail in 2- to 3-year-old children, and weaken by the age of 4 to 5 years. A trend is observed in 2- to 5-year-old children towards an increase in the average frequency of the waves that form the slow-wave nucleus. The temporal (strengthening interaction between the waves) and spatial organization of the interaction between the wave components of the “alpha”-nucleus is accelerated at the age of 4 to 5 years. The average frequency of the components forming this nucleus gradually increases with the childrens age from 4 to 7 months to 4 to 5 years. Competitive relations exist between the two nuclei, characterized by a significant decrease in the probability of transitions between the components of different nuclei. The θ2-component may play a special role of the connecting link between the nuclei at the age of 4 to 5 years, the interwave transition from the Δ- to θ-frequencies and from the latter to the α-range being effected by a leaplike rather than smooth frequency increase. The character of local and spatial rearrangements of the EEG temporal structure detected in this study reflects a gradual morphofunctional maturation of the brain as a system that maintains the specific features of self-regulation mechanisms and coordination of the intersystem interactions at various stages of a childs development.

Parameters of cerebral blood flow of 7- to 11-year-old children living in northern European Russia

Doppler sonography and rheoencephalography were used to study cerebral hemodynamics of young schoolchildren in the village of Klimovskoe (Konosha raion, Arkhangel’sk oblast, Russia). Mean linear blood flow velocities (LBVs) in the major cerebral vessels did not differ significantly from the velocities measured in age-matched children living in St. Petersburg. The index of resistivity was lower in the residents of the North than in their counterparts in St. Petersburg, which suggests a decreased tone of resistive vessels of the children living in the North. Asymmetry of the LBVs through the homonymous cerebral arteries of the left and right hemispheres was found in 67% of children examined. Asymmetry of the LBVs in the anterior, middle, and posterior cerebral and vertebral arteries (VAs) was correlated with a malformed posture (such as scoliosis or a slouch). In most children examined, sideward head rotation was accompanied by compression of VAs at the level of the C1 and C2 cervical vertebrae; in 71% of them, this condition could be regarded as a hemodynamically significant stenosis. In all children, a decreased LBV observed in one of the VAs was completely compensated by an increased LBV in its contralateral counterpart. Doppler sonographic signs of dystonic VAs and/or asymmetrical LBVs in the VAs were found in 79% of children examined. These children can be supposed to have latent disorders of blood flow in the VA basins caused by vertebral influences (related to irritation of the periarterial nervous plexus or cervical autonomic plexuses). The schoolchildren living in the North exhibited a lower reactivity of their cerebral vessels to hypo-and hypercapnia than their counterparts living in the central parts of the Russian Federation or in St. Petersburg. Regional differences were found in the sensitivity of cerebral vessels to hypocapnia. The volume of blood in the basins of the internal carotid arteries determined in a hypocapnic test was decreased; it was increased in the basins of VAs. This fact can be interpreted as a regional redistribution of the cerebral circulation caused by extreme environmental factors stimulating vital regulatory sites of the brainstem.

Spatial Synchronization of Brain Bioelectric Potentials Differs in Boys and Girls Aged 12–13 Years Reading Narrative Texts

The contribution of each cortical zone to the organization of spatial synchronization of brain bioelectric potential s (SSBP) was estimated using cross-correlation matrices of 20-channell EEG during reading in boys and girls aged 12–13 years. Differences in the topical distribution of the SSBP levels in young boys and girls were revealed both in the resting state and during reading. In boys, the SSBP level in the left temporal lobe was lower than that in girls, and in the right parietal lobe it was higher than that in girls in all the states studied. A decrease of SSBP in central cortex zones was revealed, indicating the activation of motor cortical areas in all subjects during reading. Enhancement of SSBP in the parietal regions of the left hemisphere and the occipital zones of both hemispheres is observed in boys during reading, while in girls SSBP is increased bilaterally in the frontotemporal areas with the involvement of the left frontal lobe. Moreover, during reading intrahemispheric correlations between EEGs of the central and temporoparietal regions with emphasis on the right hemisphere were more pronounced in boys, while both intra- and interhemispheric correlations of the left temporal regions were pronounced in girls.

Age-specific characteristics of EEG coherence in children and adolescents living in the European North of Russia

The article, based on the investigations carried out in 91 school students aged 7–18 years who were exposed to severe weather conditions as residents of the European North of Russia, analyzes the processes underlying the development of structures for providing the spatial synchronization of cerebral bioelectric potentials. The coherence values were evaluated for 19 channels (171 pairs of leads) in five basic EEG frequency bands (Δ, θ, α1, α2, and β). The article describes the age-related dynamics, gender-specific features, and topical specificity in the development of coherent connections in the left and right cerebral hemispheres, as well as in the formation of interhemispheric and interregional connections. We used a computerized evaluation technique for distinguishing between three school age groups of northerners using the frequency structure of EEG coherence with the purpose of elaborating some criteria for diagnosing school students with a developmental delay in the formation of spatial organization for the interaction of local EEG processes. The recorded age-related changes in the EEG-pattern structure reflect the pattern of morphofunctional brain development in children and adolescents exposed to the severe conditions of the North at different stages of their postnatal ontogenesis.

Characteristics of Integrative Brain Activity during Various Stages of Sleep and in Transitional States

Electropolygraphic study of natural night sleep was performed in 16 adult subjects using correlation, coherent, cluster, and factor analyses. New evidence testifies to the active nature of sleep, which is especially manifest during falling asleep and transition from one stage of sleep to another. Falling asleep and deepening the sleep proved to be accompanied by intense reorganization of the cortico-subcortical relationships, which is reflected in the dynamics of cross-correlative and coherent interrelationships of the brain’s bioelectric potentials. Transition from wakefulness to sleep is a heterogeneous process, which is expressed in significant changes in the weights of factors I, II and III of the vector image of multichannel EEG at stage I (B) of sleep, which might reflect changes in the contribution of the main integrative brain system in the reorganization of the brain’s integrated activity. A considerable increase in the weight of factor I (this reflects generalized the modulating effect of the brainstem on the cortex) and a decrease in the weights of factors II and III (which are related to fronto-occipital and interhemispheric interactions) testify to the special synchronizing role of the brainstem in the development of this initial stage of sleep. Deeper sleep is accompanied by a decrease in interhemispheric EEG relationships of the anterior and inferior frontal areas of the cortex, which suggests that coordinated inactivation of the cortex in both hemispheres leads to reorganization of the activity in the frontal areas. Analysis of the average variance of cross-correlative (CC) EEG relationships demonstrates that stability of the spatial structure of interrelationships between various areas of the brain cortex increases with falling asleep at stage I (A); however, during transition to stage I (B), the CC EEG values become unstable and, with deepening sleep, the variance of these values decreases in the frontal brain cortex. With the onset of the paradoxical phase of sleep, the variance of the levels of interregional interactions increases to the maximum, especially with respect to the EEG relations of the posteriotemporal and inferiofrontal areas of both hemispheres.

Age- and sex-related differences in brainstem auditory evoked potentials in secondary school students living in Northern European Russia

Brainstem auditory evoked potentials (BAEPs) were studied in 46 1st- to 11th-year students (22 boys and 24 girls) of a rural secondary school in Arkhangel’sk oblast. The objective of this work was to study age- and sex-related differences in BAEP characteristics in children and adolescents, living in the North and assess the BAEP characteristics as compared to reference values. In all three age groups of students, interpeak intervals I–III, III–V, and I–V characterizing the peripheral and central conduction times were shorter in girls than in boys. Interpeak interval III–V tended to increase with age only in boys (at puberty), with a significant increase in the latencies of waves I, III, and V. The BAEP characteristics in the subjects examined included a shorter peak latency and a greater amplitude of wave I (except senior students), relatively prolonged interpeak interval I–III, and more pronounced sex-related differences in BAEPs, especially at puberty. These findings show that it is necessary to revise regional reference values for BAEPs, differentiated by sex and age, including at puberty.

Dynamics of heart rate response in sleeping infants exposed to tone stimuli

Heart rate, EEG, and motor responses were recorded following presentation of a series of 6–10 sound stimuli (2.5-s tones of 1000, 4000, and 250 Hz, 70 dB, interstimulus intervals 18–25 s) in neonates aged 9 to 22 weeks during stage 2–3 sleep. The infants (17 of 19) revealed heart rate (HR) changes in response to tone stimuli that consisted in an expanded form of three phases: (1) short-latency (at 1 s after tone presentation) HR deceleration, (2) HR acceleration with a maximum at 3–5 s, and (3) late HR deceleration at 6–9 s of the poststimulus interval. The occurrence rate of the first two phases of cardiac response is relatively constant during a series of stimuli, whereas the likelihood of late HR deceleration is the highest following the first tone presentation and decreases significantly when the stimulus is repeated. Differences in the dynamics and statistical analysis allow a relative independence of all the three response phases to be suggested. The HR acceleration phase is dramatically enhanced in association with the motor response elicited by the sound stimulus. The late HR deceleration phase occurs not only after the first presentation of stimuli, but also when they are repeated if they evoke EEG reaction (vertex potentials) in response to both the beginning and end of the tone sound. Possible mechanisms of the three phases of poststimulus HR changes are: the vagal cardiac reflex associated with the acoustic (adaptive) reflex, activation of sympathetic efferents in combination with the startle reflex, and secondary vagal deceleration of sinus rhythm likely to be associated with the processes of perception (detection) of a “novel” stimulus and to serve as an indirect sign of an orienting reaction.