PROCEEDINGS IPMU '08
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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