The aim of this study was to determine electroencephalogram (EEG) in a session of heart rate variability biofeedback (HRV BF) in adolescents with different Internet addiction (IA) risks. In total, 100 healthy adolescents aged 16–17 years with minimal risk of IA (Group I, 35%), pronounced risk of IA (Group II, 51%), and stable pattern of IA (Group III, 14%) using the Chen Internet Addiction Scale were examined. HRV and EEG parameters were determined at baseline (5 min), and then during the short-term HRV BF session (5 min), in order to increase the total power (TP, ms²) of the HRV spectrum. Against the background of an increase in the TP and a decrease in sympathetic activity, an increase in alpha EEG was revealed, especially in Groups I and II. The greatest increase in the power of beta₁-activity of EEG in the frontal, central, and temporal brain regionswas found in Groups I and II. In adolescents with a pronounced risk of IA, HRV BF is accompanied by a severe activation of the brain systems, while in persons with a stable type of IA, the least brain reactivity is shown, especially in the beta₁ EEG band.

Age features of autonomic nervous regulation of cardiac activity in 426 healthy adolescents aged 14-17 years living in areas of different latitudes, climatic and ecological conditions of the European North - in the Subpolar (64°30' N) and Polar (67°40' N) areas have been detected. Assessment of the cardiovascular system status was carried out with the use of the heart rate variability (HRV) and blood pressure (BP) parameters. The share of persons with borderline hypertension (BP level exceeded the limit of 90 percentile) also increased with age and reached 63% by the age of 17 years. Among the adolescents living in the Polar region according to the HRV and blood pressure indices, there was registered a significant increase in the proportion of persons with a predominance of sympathetic influences on the heart activity. The greatest adrenergic effects on the cardiovascular system were found in the 15-year-old adolescents of the Polar region, they had higher indices of systolic blood pressure, the heart rate and the regulatory systems stress index, as well as lower total HRV spectrum power in comparison with the 15-year-olds adolescents living in the Subpolar region.

Synchronization between heart rate variability (HRV) in the low-frequency (LF) range (0.04–0.15 Hz) and 1-min variations in the components (X, Y, Z)and the total vector (F) of geomagnetic induction (nT) was studied in normotensive (blood pressure up to 140/90 mmHg) and hypertensive (blood pressure above 140/90 mmHg) individuals living in the Arkhangelsk region (60°51′52″ N 39°31′05″ E).The duration of registration of HRV for each person is 30 min in a sitting position. The most pronounced synchronization of the LF parameter, which reflects baroreflex activity, with variations in the GMF was found in normotensive individuals. The absence of a significant synchronization of the LF parameter with variations in the GMF components indicates a decrease in the sensitivity of the baroreflex mechanism and a risk of dysregulation of vascular tone, especially in people with arterial hypertension, under conditions of instability of the geomagnetic field.

The review contains a definition and the essence of biofeedback functional methods. The historical, scientific aspects and the main hypotheses are given here explaining the mechanisms of biofeedback. Different techniques and methods of biofeedback are discussed, as well as the scope of the rapidly developing technology of biofeedback. Emphasis is put on physiological mechanisms and prospects of heart rate variability biofeedback methods of development.