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.

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 func tional 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 determi nation 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 cosmophys ical factors under the extreme conditions of high latitudes; however, response pattern and intensity depended on individual sensitivity to their isolated and combined effects.

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.

The central mechanisms of involuntary and voluntary regulation of attention in schoolchildren from the northern region were studied using a method based on the P300 wave of evoked brain potentials (the oddball paradigm). Data were compared with results obtained from psychological tests. Differences in the organization of EP were seen in the "passive" and active (counting) perception of deviant stimuli. Three components were identified within the time envelop of the P300 wave, two of which dominated in the frontal and one in the parietal area of the cerebral cortex. The latency of the P300 wave decreased with age in the children, reflecting increased rates of information processing and increases in the volume of operative memory. In passive perception, the statistical relationship characterized by a reduction in P300 latency with age was significant for leads in the central, temporal, parietal, and occipital areas; in active perception, this applied to all areas including the frontal. The most significant changes in P300 parameters were seen in children aged from seven to 12 years, indicating that this period can be regarded as "critical" in the development of learning skills. The roles of the parietal and frontal areas of the cortex in the mechanisms of involuntary and voluntary regulation of attention are discussed, along with the possibility of using the P300 method to identify children with delayed rates of development of voluntary attention in population studies.