The reorganization in EEG spectra and cortical connections during spatial and verbal thinking

Solution of spatial and verbal tasks was studied in 43 subjects using the advanced version of the method of intracortical interaction mapping (IIM) and analysis of EEG spectra in short (250 ms) intervals. Comparison between the IIM and coherence methods during solving simple motor tasks revealed some advantages of the IIM for studying of labile cortical connections. Several stages were separated in the process of solution of the mental task in accordance with patterns of cortical connections. The duration of the stages was similar in both kinds of tasks and corresponded to that revealed in psychological experiments. Cortical connections in the theta range were generalized and reflected the level of general tension. This unspecific tension was high for the whole period of the spatial task solution while in the verbal task the tension increased to the stage of decision making. Task-specific patterns were revealed in the beta range. The right parietal and temporal regions were the centers of EEG connections during solution of the spatial task while the left central area was essential for the verbal task solution. The left parietal area was involved in solution of both kinds of tasks. The frequency parameters of connections in the beta range were stable during the spatial task solving, and in the process of verbal task solving the dominant frequency changed after the initial (perception) stage probably due to switching to another thinking mechanism.