Analysis of brain activities and investigation of hierarchical language processing

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The research is aimed at elucidating spatiotemporal neural activities during sentence reading. To analyze multiple activities within the brain, minimum L1 norm reconstruction was examined by simulation. It was found that the locating accuracy was within about 5 mm when a gravitational center of estimated dipole sources was computed, where the standard error was about 15 mm. The dipole moments, which were estimated for multiple subjects, were averaged by using Gaussian function with the above standard error in standard brain coordinates, which enabled visualization of distributed brain activities.In MEG measurements we used Japanese complex sentences that included a main clause, in a canonical phrase-order of subject (S) - object (O) -verb (V), combined with a subordinate clause. Sentences that had the main clause of scrambled O-S-V phrases were also composed and mixed. Those sentences were presented visually phrase-to-phrase to subjects. They performed a judgment task during MEG record … More ing, answering a question given in canonical-order phrases about the thematic role, i.e., "who did whom what" of the main clause. MEG responses of different phrases in the main clause were averaged, from which distributed current sources were estimated by L1 norm method.Grand mean distribution across eleven subjects of the localized sources showed regional activities focused in the prefrontal and posterior temporal areas in the left hemisphere, which may overlap with classical language areas. Activities were also found around the left central sulcus, indicating sensory/motor cortices, centered at the hand area. These active regions, together with visual occipital cortices were observed in most subjects, though large inter-subject varialbilities existed in the magnitude and extent of the activities. Posterior part of the prefrontal area and the sensory/motor areas were more active for scrambled than canonical sentences. No focal activities in the central and prefrontal regions were observed in the right hemisphere. Less