Discrimination of mental translation by EEG: An equivalent current dipole source localization approach

T. Yamanoi, H. Toyoshima, S. Ohnishi, T. Yamazaki, M. Sugeno, E. Sanchez

To investigate the brain activity during human recognition of characters and symbols with directional meanings, the authors recorded electroencephalograms (EEGs) from four subjects in viewing and mental translating four types of characters (Kanji: Chinese characters being used currently in the Japanese language) and four symbols (arrow) presented on the CRT which means direction for Upward, Downward, Leftward and Rightward. EEGs were averaged for each stimulus type, and event related potentials (ERPs) were obtained. On comparing ERPs of kanji characters with those of arrow symbols with opposite meanings, peak latencies for marked amplitude changes were predominantly similar, but polarities were opposite. The equivalent current dipole source localization (ECDL) method was applied to these ERPs, and ECDs were estimated by use of the ECDL. The ECD was estimated at a latency of around 110 ms in the MT (V5) area and then around 300 ms in the precentral gyrus. No remarkable differences in this tendency were noted among the eight stimuli. After localization of ECDs to the precentral gyrus, with the kanji characters, ECD was localized to the right middle temporal gyrus regardless of direction. ECD was then estimated in areas related to language, such as the Wernicke’s area in the left middle temporal gyrus, the left angular gyrus and the left lingual gyrus. ECD was later localized to the left middle frontal gyrus, the left inferior frontal gyrus and the prefrontal area. ECD was estimated in the precentral gyrus just before the amplitude of ERPs changed remarkably. With arrow symbols, ECD was localized to the right middle temporal gyrus, and then it was estimated in areas related to the working memory for spatial perception, such as the right inferior or the right middle frontal gyrus. Then, as with kanji characters, ECD was localize to the prefrontal area and the precentral gyrus. In case of the mental translation, activities were observed on the area around the same latency regardless to the Kanji or the arrow. After on the right frontal robe, which is socalled the working memory, ECDs were localized to the Broca’s area which is said to be the language area for speech. Like in our preceding researches, the moment of ECD was almost opposite in each other case of opposite meanings. This fact is useful for the brain machine interface. We might control a machine by EEGs.

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