The Dynamics of the Baseline Brain State Vary Among Different Subjects Under the Influence of Cognitive Tests and Blood Glucose Levels Changes

Based on individualized resting EEG analysis, we studied how changes in blood glucose levels as well as performance of a cognitive task affect the background brain state. Twenty-four healthy adults aged 18–35 performed a word classification test twice: once in a fasting state and once after glucose intake. EEG recordings were analyzed in resting-state conditions with eyes closed (EC) and eyes open (EO), before and after the test at each stage. Changes in integral parameters derived from the structural function of multichannel EEG were evaluated. These parameters served as measures of the spatial (pS) and temporal (pT) organization of EEG activity. Individual analysis revealed significant changes in pT and pS parameters in all participants due to increased glucose levels and the cognitive task, with a significant interaction effect between these factors. Group-averaged results masked these effects due to the variability in individual responses. On an individual level, performing the cognitive test after glucose intake led to a significant increase in pS for most participants, indicating higher differentiation and reduced spatial coherence of EEG processes. This was accompanied by a significant linear correlation between the increase in pS and the reduction in reaction time, suggesting heightened CNS activation. This effect was more pronounced in the eyes-open condition than with eyes closed. A positive correlation between fasting blood glucose levels and pT values was found. After the test, a tendency for pT to increase—reflecting reduced temporal coherence and potentially indicating enhanced functional flexibility of neural processes—was observed. The proposed method for calculating integral parameters that characterize spatial and temporal coherence in multichannel EEG can be used to monitor and study changes in the brain’s functional state during cognitive activity and the effects of substances affecting brain metabolism.