## 3 Results
At all stages of the experiment, in all frequency ranges in Figure 3, higher coherence values were found in the frontal, central, and parietal EEG leads compared with the occipital leads. Figure 3e-h shows the differences between the coherence coefficients at stages S1 and R1, and stages S2 and R2. In all leads, the coherence between \(\delta_{1}\)oscillations in EEG is statistically significantly less by 14 (\(-\)1; 29)% at the stress stage S1 than at the rest stage R1 and is significantly less by 17 (0; 27)% at the stress stage S2 than at the rest stage R2 in all leads except O1 (Figure 3e). The coherence between \(\delta_{2}\)oscillations in EEG is statistically significantly less by 10 (\(-\)2; 24)% at the stress stage S1 than at the rest stage R1 in frontal, central, and occipital EEG leads (Figure 2f). At the same time, there was no significant change in coherence between \(\delta_{2}\)-oscillations in EEG at stage S2 in comparison with stage R2 (Figure 2f). The coherence coefficients of \(\delta\)-oscillations in EEG showed a significant increase of 7 (\(-\)2; 17)% at stage S1 and of 10 (2; 19)% at stage S2 only for central and parietal leads (Figure 2g). The coefficients of coherence between \(\theta\)-oscillations in EEG were not so sensitive to stress. Significant changes in these coefficients were found only for a few leads during stage S2 (Figure 3h). Figure 4a-d shows statistically significant changes in coherence between pairs of EEG leads. In \(\delta_{1}\)-range, the stress stages S1 and S2 are characterized by a decrease in intrahemispheric coherence compared with the R1 and R2 stages of rest, respectively (Figure 4a). At stage S2, a decrease in interhemispheric coherence between the frontal, central, and parietal leads is observed in the \(\delta_{1}\)-range. Additionally, an increase in coherence between the occipital leads takes place (Figure 4a). In the \(\delta_{2}\)-range, a decrease in intrahemispheric coherence is also observed during stress-inducing stages S1 and S2 (Figure 4b). However, stage S1 is characterized by a decrease in interhemispheric coherence between the frontal leads and an increase in the occipital, parietal, and central leads. In stage S2, an increase in all interhemispheric coherence coefficients is observed (Figure 4b). In the \(\delta\)-range of EEG, a decrease in intrahemispheric coherence during stress is less pronounced than in the \(\delta_{1}\)-range and the \(\delta_{2}\)-range (Figure 4c). Interhemispheric coherence increases in the \(\delta\)-range during both stress stages S1 and S2 (Figure 4c). In the \(\theta\)-range, an increase in interhemispheric coherence is seen in response to the stress at stage S2 (Figure 4d). Table 1 presents the medians and the first and third quartiles of individual differences in interhemispheric and intrahemispheric coherence coefficients at stages S1 and R1, and stages S2 and R2. A negative median value indicates a decrease in coherence at the stress stage and a positive median value indicates an increase in coherence during stress. Figure 3: (**a–d**) Medians of distributions in the ensemble of mean values of the coherence between EEG leads in (**a**) \(\delta_{1}\)-range, (**b**) \(\delta_{2}\)-range, (**c**) \(\delta\)-range, (**d**) \(\theta\)-range at R1, S1, R2, and S2 stages of the experiment. (**e–h**) Differences in coherence coefficients at stages S1 and R1, and stages S2 and R2 in: (**e**) \(\delta_{1}\)-range, (**f**) \(\delta_{2}\)-range, (**g**) \(\delta\)-range, (**h**) \(\theta\)-range. Circles indicate the EEG leads that demonstrated statistically significant differences between the stages of rest and stress, while crosses indicate the EEG leads in which these differences were not statistically significant. The results of the analysis of the structure of directional couplings between EEG leads are presented in Figure 4e-h. It can be seen that in general, the changes in directional coupling indices during the stages of stress agree well with the changes observed in the phase coherence coefficients in Figure 4a-d.