## 4 Discussion  
In this paper, we studied in detail the influence of stress-inducing cognitive tasks on the infra-slow oscillations of brain potentials. We previously obtained indirect evidence of the influence of stress on the power spectral density of EEG signals in the low-frequency range [16]. However, the present study revealed, for the first time, statistically significant changes in the power of infra-slow oscillations in EEG signals in response to the development of moderate stress. The results of oscillations in the \(\alpha\)-range and \(\beta\)-range of EEG signals obtained in this study agree with the results of other studies [52; 53; 54; 55; 56; 57; 59; 60]. For example, it was shown that \(\beta\)-activity in the frontal and temporal areas was significantly higher in the non-stress group than in the stress group under emotionally unpleasant stimuli [60]. However, the spectral indices of \(\delta_{1}\)- activity and \(\delta_{2}\)-activity showed a much higher sensitivity to stress (Figure 2). Thus, analysis of the power of infra-slow oscillations of brain potentials for the diagnostics of stress is promising. Power distribution by EEG leads qualitatively differs in different frequency ranges, which indicates that different mechanisms cause the identified changes. Oscillations in the \(\delta_{1}\)- and \(\delta_{2}\)-ranges have maximal power in the frontal EEG leads (Figure 2a,b), which is probably due to their location above the prefrontal cortex, which is associated with the activity of the sympathetic and parasympathetic nervous systems [60; 61]. \(\alpha\)-oscillations have maximal power in parietal EEG leads (Figure 2c) that can be explained by a change in the activity of the corresponding cortical structures when focusing attention [62]. The \(\beta\)/\(\alpha\) ratio is maximal in the occipital EEG leads (Figure 2d) that is often interpreted as activation of the cortical structures responsible for processing cognitive information [63]. The results of the analysis of couplings between EEG leads in the frequency range <0.5 Hz are also of interest. It was reported that the development of stress is accompanied by a decrease in intrahemispheric couplings and an increase in interhemispheric couplings in the \(\delta\)- and \(\theta\)-ranges [20; 22; 64]. Our results are consistent with these findings (Figure 4c,d,g,h). Moreover, analysis of the connectivity of infra-slow oscillations of brain potentials, performed for the first time in this study, also demonstrated a significant decrease in intrahemispheric couplings under stress (Figure 4a,b,e,f). The interhemispheric couplings between EEG leads also increased during stress in the \(\delta_{2}\)-range as well as in the \(\delta\)- and \(\theta\)-ranges. However, in the \(\delta_{1}\)-range, the interhemispheric couplings decreased under stress (Figure 4a,e). This can probably be explained by the nature of oscillations in the \(\delta_{1}\)-range associated with the processes of sympathetic control that respond to the development of stress [1; 7; 33; 34; 35]. Comparison of changes in couplings of EEG leads indicates that the decrease in intrahemispheric couplings in response to stress is most pronounced in the \(\delta_{1}\)- and \(\delta_{2}\)-ranges (Figure 4a,b,e,f) and least pronounced in the \(\theta\)-range (Figure 4d,h). During the SCWT (stage S1), the changes in interhemispheric couplings are most pronounced in the \(\delta\)-range (Figure 4c,g) and least pronounced in the \(\delta_{1}\)-range (Figure 4a,e). During the MAT