A change in the human psychophysiological state, caused by stress in particular, affects the processes of autonomic control, the activity of which is reflected in infra-slow oscillations of brain potentials with a frequency of less than 0.5 Hz. We studied the infra-slow oscillations in scalp electroencephalogram (EEG) signals in the frequency ranges of 0.05–0.15 Hz and 0.15–0.50 Hz that are associated with the processes of sympathetic and parasympathetic control, respectively, in healthy subjects at rest and during stress-inducing cognitive tasks. The power spectra of EEG signals, the phase coherence coefficients, and indices of directional coupling between the infra-slow oscillations in the signals of different EEG leads were analyzed. We revealed that, compared with the state of rest, the stress state is characterized by a significant decrease in the power of infra-slow oscillations and changes in the structure of couplings between infra-slow oscillations in EEG leads. In particular, under stressful conditions, a decrease in both intrahemispheric and interhemispheric coupling between EEG leads occurred in the range of 0.05–0.15 Hz, while a decrease in intrahemispheric and an increase in interhemispheric couplings was observed in the range of 0.15–0.50 Hz.

Anesthesia enables the painless performance of complex surgical procedures. However, the effects of anesthesia on the brain may not be limited only by its duration. Also, anesthetic agents may cause long-lasting changes in the brain. There is growing evidence that anesthesia can disrupt the integrity of the blood–brain barrier (BBB), leading to neuroinflammation and neurotoxicity. However, there are no widely used methods for real-time BBB monitoring during surgery. The development of technologies for an express diagnosis of the opening of the BBB (OBBB) is a challenge for reducing post-surgical/anesthesia consequences. In this study on male rats, we demonstrate a successful application of machine learning technology, such as artificial neural networks (ANNs), to recognize the OBBB induced by isoflurane, which is widely used in surgery. The ANNs were trained on our previously presented data obtained on the sound-induced OBBB with an 85% testing accuracy. Using an optical and nonlinear analysis of the OBBB, we found that 1% isoflurane does not induce any changes in the BBB, while 4% isoflurane caused significant BBB leakage in all tested rats. Both 1% and 4% isoflurane stimulate the brain’s drainage system (BDS) in a dose-related manner. We show that ANNs can recognize the OBBB induced by 4% isoflurane in 57% of rats and BDS activation induced by 1% isoflurane in 81% of rats. These results open new perspectives for the development of clinically significant bedside technologies for EEG-monitoring of OBBB and BDS.

We investigated individual dynamics of cognitive performance and heart rate variability (HRV) measures during prolonged mental load. The aim of this study was to identify characteristic phases of cognitive performance and individual patterns of physiological responses induced by prolonged mentally fatiguing tasks. In prolonged experiments with two cognitive tasks of different structure, cognitive performance, HRV measures, and subjective fatigue were analyzed. The proposed integrated index of relative performance made it possible to identify individual phases of cognitive performance: the adaptation phase (AP), the optimal performance phase (OP), and the fatigue phase (FP). The OP was observed in all subjects, the FP in most subjects, whereas the AP was observed in fewer than half of the subjects, indicating pronounced inter-individual variability in cognitive performance dynamics. Two patterns of the initial heart rate (HR) response were identified, ΔHR ≥ 0 and ΔHR < 0, which were associated with differences in the subsequent dynamics of HR and individual HRV measures. The nature of these differences depended on the phase of cognitive performance and the type of task. Among subjects who performed both tasks, approximately half showed the same direction of the initial HR response in the Serial Subtraction Task (SST) and the Working Memory Task (WMT), whereas the remaining subjects showed different directions, indicating limited reproducibility across tasks. The obtained results demonstrate pronounced inter-individual variability in cognitive performance and physiological responses during prolonged mental load and support the need to account for individual dynamics when developing personalized approaches to monitoring mental fatigue.