Dynamic excitation of cortical areas during visual information processing

In order to study neural processing of the visual films that are related to language function in the human brain, we measured magnetoencephalograpic (MEG) responses while subjects performed perception/recognition tasks of words, characters, and symbols. The sites of cerebral neural activities were estimated by localizing equivalent current dipole sources (ECD), i.e., generators of the MEG responses within the individual brain structure in the MR images. Two-to-three distinct components were observed in the waveform of the measured MEG responses, whose peak latencies were between 150 and 300 ms after the onset of the visual form. In some subjects dynamic excitation of the cerebral neural activity was visualized as the spatiotemporal movement of the localized ECD during a period of 50-100 ms. The neural activity proceeded from the occipital to temporal area for words or to inferior parietal area for symbols in a manner that depended on the visual form, suggesting specific pathways of the visual information processing.