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The features of the electroencephalogram (EEG) at the heart rate variability single biofeedback session in adolescents aged 15-17 years living in the subpolar and polar northern regions were determined. In adolescents of the subpolar region identified shaped age EEG pattern. We have established higher diencephalic and subcortical brain structures activity manifested in the elevated theta-activity levels and the diffuse photic driving reactions in adolescents of the polar region than in adolescents of subpolar region. In the dynamics of the biofeedback sessions in both regions there were identified groups of persons with both increased alpha-activity spectral power and decreased of it. After biofeedback sessions in adolescents of polar region more prolonged increase of alpha-activity, more pronounced reduction of theta-activity and the photic driving reactions were revealed. Changes in EEG patterns are most characteristic of the right brain hemisphere involving the frontal brain areas.

The morphofunctional age-related development of the brain was studied in schoolchildren living in the difficult climatological-geographic and socioeconomic conditions of the north (Arkhangel'sk region). Of the 62 students in country middle schools, EEG amplitude-frequency, time, and spatial measures corresponded to age norms (European norms) in only 10 cases (16%). A further 26 children (53%) showed minor abnormalities in the form of an inadequate degree of organization of the temporospatial EEG pattern, mainly in the frontal and temporal lobes of the brain, with increases in the levels of the theta and delta rhythms, and the absence of any marked "functional nucleus" in the alpha rhythm. In the remaining 14 children (29%), EEG measures showed more marked delays in mental development (DMD), which were combined with learning difficulties and abnormal behavior. The retardation in the morphofunctional development of the brain in northern children averaged 1.5-2 years, which coincides with delays in hormonal and physical development described by other authors.