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Hemispheric specialization for the linguistic process was studied by the 'entropy analysis' method which distinguishes the direction of information flow for mutually coupled time series. Meaningful and non-meaningful stimuli were presented to 14 subjects. EEGs were recorded from homologous Wernicke's and occipital areas in the two hemispheres. The amount of information flow both from the left to right hemisphere and from the right to left hemisphere was obtained under the 3 conditions (i.e., meaningful, non-meaningful and resting baseline conditions) in each area. The information flow from the left to right hemisphere was significantly larger under the meaningful condition than from the right to left hemisphere in Wernicke's area, but no significant differences in the information flow could be found between the two directions under the non-meaningful condition in Wernicke's or the occipital area. Therefore, the dominant direction of the left to right hemisphere was observed under the meaningful condition in Wernicke's area but not in the occipital (non-speech) area, while no dominant direction was observed under the two control (i.e., non-meaningful and baseline) conditions in either area. These results may suggest that the dominant direction of information flow with the meaningful stimuli is related to linguistic meaningfulness in Wernicke's area.

The direction of spread of alpha activity over the scalp was studied using the modified 'entropy analysis' method which distinguishes the direction of time differences between two correlated signals in the alpha band. The resting EEG was recorded from F3, F4, C3, C4, P3, P4, O1 and O2, each referenced to linked ears in 10 subjects. The directed measure of correlation of alpha activity in two directions (e.g., from O1 and O2 and from O2 to O1) was obtained from all possible pairs of electrodes. The dominant longitudinal direction of alpha activity was found to be anterior to posterior within as well as across hemispheres. No dominant transverse direction was found. This suggests that the spread of alpha activity over the scalp is in the dominant anterior-posterior direction.

Source determination of alpha activity was studied using the relative power contribution analysis (RPCA) method which allows determination of the relative contributions of different areas to the power of a certain area at different frequencies. In 20 normal subjects, EEGs were recorded from F3, F4, C3, C4, P3, P4, O1 and O2, each referenced to a linked ear. An 8-dimensional autoregressive model was fitted to the EEGs of 10.24 sec. Based on the model, RPCA was performed. For each area, alpha activity was divided into two parts: one originating in its own area (endogenous) and another in the other areas (exogenous). Endogenous alpha activity increased as the area was more posterior. In the anterior regions (frontal and central), endogenous alpha power (power of endogenous alpha activity) was small, while exogenous alpha power was large. In the posterior regions (parietal and occipital), the amount of endogenous alpha power did not differ markedly from that of exogenous alpha power. The posterior regions, which generate more endogenous alpha activity, can be considered to play a dominant role in alpha generating mechanisms. In some subjects, alpha generators with a different frequency from that of the occipital areas were observed.