The study is aimed at assessing individual and age-related features of the functional state of various parts of the brain and the patterns of their ontogenetic changes based on the structural analysis of resting-state electroencephalogram (EEG) patterns in 5- to 7-year-old children. The study involved 266 children, who were divided into different age groups: Group 1–5 years old (mean age 4.98 ± 0.33), Group 2–6 years old (mean age 6.03 ± 0.35), and Group 3–7 years old (mean age 6.85 ± 0.22). Alpha-rhythm parameters recorded mainly in the occipital areas may serve as an indicator for the functional maturation of the brain. Significant age-related changes in the alpha-rhythm parameters have been revealed. The presence of a regular alpha-rhythm with a frequency of 8 to 10 Hz increases from 5 to 7 years of age. The occurrence of the alpha-rhythm of reduced frequency significantly decreases by the age of 7 years, and the occurrence of the polyrhythmic alpha-rhythm – by the age of 6 years. These changes are caused both by complications of the structural and functional organization of the cerebral cortex at the cellular level, which occur throughout the studied age period, and the improvement of its relationships with subcortical structures. A decrease in the occurrence of high-amplitude alpha-range electrical activity (EA) with signs of hypersynchrony in the caudal regions may indicate the maturation of the system of nonspecific activation of the brainstem reticular formation from 5 to 7 years of age. Age dynamics is also manifested in a significant decrease in the EEG occurrence of theta-range EA, and its zonal distribution in 5- to 7-year-old children aged. Such changes specify the process of progressive formation of functional connections between individual areas of the cortex, as well as the cortex and subcortical structures, in particular thalamo-cortical ones. The occurrence of alpha-range EA (less than 5.0%) and beta-range EA (about 13.0%) arranged topographically in the anterior cortex did not differ significantly with age. However, generalized EEG activity in the form of different frequency range waves, which characterizes the functional state of predominantly hypothalamic structures, occurs reliably more often in 7-year-old children rather than in 5-year-old children. Such dynamics is presumably associated with an increased reactivity of the hypothalamic-pituitary system in response to adaptive stresses caused by the transition to systematic learning and can be considered as a distinctive feature of this age period. Due to great restructuring of the brain functioning, all its structures become especially sensitive to high intellectual and emotional stress, which is characteristic of preschool children nowadays. The novelty of this study is highlighted by the identification of patterns, structure and nature of EA changes in 5- to 7-year-old normotypical children’s brain to assess the functional state of the cortex and regulatory brain systems. The research results based on a large sample of children, growing up in modern social and cultural conditions, would provide guidance for the formation of age standards.
