Spatial and frequency differences of neuromagnetic activities between the perception of open- and closed-class words

The present study investigated the spatial and frequency differences of neuromagnetic activities between the perception of open- and closed-class words by using a 275-channel whole head magnetoencephalography (MEG) system. Two groups of words, 110 open-class and 110 closed-class, were presented visually and auditorily simultaneously. The data of 12 healthy subjects were analyzed with synthetic aperture magnetometry (SAM) which can identify the frequency-dependent volumetric distribution of evoked magnetic fields (EMFs). Both vocabulary classes elicited spectral power changes in the left inferior frontal gyrus (Broca's area) and left posterior-superior temporal gyrus (Wernicke's area) within 70-120 Hz. However, the open-class words elicited event-related desynchronization (ERD) while the closed-class words elicited event-related synchronization (ERS) in the two areas within 70-120 Hz. In addition, the open-class words also elicited ERS in the right inferior frontal gyrus, right middle frontal gyrus and right inferior parietal lobe within 1-8 Hz, but the closed-class words only elicited ERD in the right inferior frontal gyrus within 1-8 Hz. Furthermore, there were ERD in the right posterior-superior temporal gyrus within 120-200 Hz for the open-class words, but not for the closed-class words. These results indicate that open- and closed-class words are processed differently in the brain, not only in the anatomical substrates, but also in the frequency range of neuromagnetic activity.