LOCALIZATION OF ACTIVATED AREAS AND DIRECTIONAL EEG PATTERNS DURING MENTAL ARITHMETIC

In a search for the physiological correlates of mental activity, local ized EEG desynchronization induced by mental arithmetic was assessed b y the entropy of the EEG power spectrum (irregularity index, II). The topographic mapping of II can show a localized cortical activation. Di rectional EEG patterns during mental arithmetic were further examined with a directed mutual information measure (information flow). These t wo information measures were compared between resting and mental arith metic conditions in 10 right-handed subjects as well as one left-hande d subject. II significantly increased during mental arithmetic in the left temporo-centro-parietal region in right-handed subjects. thus exh ibiting its activation. Significant changes in information flow during mental arithmetic were found in the directions mostly from the tempor o-centro-parietal region to other areas and within the frontal region in right-handed subjects: information flow from the left temporal and the mid-frontal areas increased and information flow mostly from the l eft hemisphere decreased. One left-handed subject showed greater II in the right temporo-parietal area and smaller II in the left temporal a rea during mental arithmetic, together with smaller information flow f rom the right post-temporal area. These findings suggest that the left temporo-centro-parietal activation is specific to calculation process ing, and the frontal information flow is related to the active perform ance of mental arithmetic.