The aim of the study was to reveal longitudinal changes in electroencephalogram spectral power and frequency (percentage frequency composition of EEG and alpha peak frequency) patterns in normal children from northern Russia. Fifteen children (9 girls and 6 boys) participated in the study. The resting state (eyes closed) EEGs were recorded yearly (2005-2013) from age 8 to age 16-17 for each child. EEG frequency patterns were estimated as the percentages of waves with a 1 Hz step revealed by measuring the interval durations between points crossing zero (isoline) by a curve. EEG spectral power changes were analyzed for delta (1.5-4 Hz), theta (4-7.5 Hz), alpha-1 (7.5-9.5 Hz), alpha-2 (9.5-12.5 Hz), beta-1 (12.5-18 Hz) and beta-2 (18-30 Hz) bands. According to the frequency composition of the EEG signals fast synchronous, polymorphous synchronous, polymorphous desynchronous and slow synchronous types of children EEG were revealed. These EEG types were relatively stable during adolescence. In these EEG types, the frequency patterns and spectral power dynamics with age had several common and specific features. Slow wave percentage and spectral power in the delta band remarkably decreased with age in all groups. Starting from the theta band the EEG types were characterized by different EEG spectral power changes with age. In fast synchronous EEG type, the theta and alpha-1 EEG power decreased, and the alpha-2 power increased in the occipital and parietal areas. The polymorphous synchronous type was characterized by increased both the alpha-1 and alpha-2 power with regional peculiarities. In the polymorphous desynchronous type spectral power in all bands decreased with age, and in the slow synchronous type, the alpha-1 power massively increased with age. Obtained results suggest predictive strength of the spatial-frequency patterns in EEG for its following maturation through the years.

The mechanisms regulating the functional state (FS) of the brain were studied in humans in conditions of dosed acute hypoxia (breathing a mixture of 8% oxygen in nitrogen for 15-25 min). The dynamics of the FS of the brain due to changes in the balance of the activities of brain regulatory structures in hypoxia were reflected in rearrangements of EEG spatial relationships (factor and cluster analysis of EEG crosscorrelation matrixes) and the redistribution of intracerebral locations of electrically equivalent dipole sources (EEDS), with increases in EEDS density in the projections of the medial and basal parts of the temporal lobes of the hemispheres (EEDS tomography data). Changes in cortical-subcortical interactions were characterized by a decrease in the tone of the activatory brain system, a decrease in the inhibitory control of subcortical structures by neocortical formations, and activation of limbic system and hypothalamic structures. Switching of the integrative regulatory mechanisms from the cortico-thalamic level to the limbic-diencephalic level may allow release of the energy-consuming nonspecific components of hypoxic stress and more stable regulation of physiological parameters by the major vital systems in conditions of increasing oxygen deficit.

Results obtained from complex medical-physiological investigations performed during 10 scientific expeditions in the Arkhangel'sk Region in 2003-2005 are presented. The effects of climatological-geographic, biogeochemical, and social conditions of the conditions obtaining in the Far North region of Russia on sexual maturation, formation of the structural-functional organization of the brain, autonomic functions, and immunological and biochemical status of schoolchildren were studied using state-of-the-art neurophysiological methods (computerized electroencephalography, computerized rheoencephalography, computerized electric dipole origin tomography, etc.), psychophysiological and psychometric methods (assessment of the state of cognitive and memory functions, Wechsler intellectual scale), along with biochemical assay of monoamine oxidase (MAO, the key enzyme in adrenergic neurotransmitter metabolism) and the liver enzyme butyrylcholinesterase (BuChE) and physicochemical analysis of the levels of macroelements and trace elements in the body.

The formation of physiological functions and the development of the body as a whole occur on the background of a close interaction between the body and the environment [13]. Thus, developmental processes at different stages of ontogeny are adaptive in nature and are determined by two very important factors: the morphofunctional maturity of physiological systems and the appropriateness of environmental factors to the functional potentials of the body [10,23].Concepts of the adaptive nature of development and the mechanisms of the systems organization of adaptive reactions are linked with questions of the sensitive and critical periods of development. A particular role is played by criteria reflecting the level of development and qualitative changes in adaptive mechanisms associated with the maturation of different parts of the brain, including the regulatory structures of the central nervous system. Structural-functional changes in the brain provide the basis for rearrangements of bioelectrical activity during ontogeny. The EEG has been found to have high prognostic value for identifying the functional level of "brain maturity" [6,8,32,34]. EEG analysis identified a series of key ("critical") periods of CNS development [1,38].The nature of brain bioelectrical activity is to a significant extent genetically determined. The genotype has been shown to have a significant role in forming the amplitudefrequency characteristics of the EEG [11,25], and data have been obtained on the genetic determination of individual characteristics of the spatial organization of the EEG [12,26]. The effects of complex natural-climatic and social-domestic conditions imposing increased requirements on physiological systems induce not only functional deviations due to the state of pressure on the regulatory systems in children's Traditional and original analytical methods were used to study the developmental characteristics of EEG dynamics in 156 children and adolescents aged 7-17 years of the aboriginal (Koryaks, Evens) and offspring of settler (Europeoid) populations living in the severe climatogeographical conditions of the northeast of the Russian Federation. New data were obtained on the age-and gender-related and ethnic characteristics of the formation of brain bioelectrical activity. EEG markers were identified characterizing changes in the structure of interactions between EEG rhythms. Developmental rearrangements of this structure were found to occur at different times for different cortical areas and frequency ranges, with onset 2-3 years later in children of the aboriginal population than in offspring of the settler population. It is suggested that these differences reflect the genophenotypic characteristics of the morphofunctional development of the CNS in children of the aboriginal and settler populations on the background of increased adaptive pressure in extreme environmental conditions.