Time course and localization of brain activity during numerical processing in grapheme color synesthesia, an ERP and sLORETA study

[Speaker] Shibata, Midori:1
[Co-author] Fukuzaki, Sa-ya:2, Sato, Arisa:3, Umeda, Satoshi:1,2
1:Keio Advanced Research Center, Keio University (Japan), 2:Department of Psychology, Keio University (Japan), 3:Graduate School of Human Relations, Keio University (Japan)

Grapheme-color synesthesia is a perceptual phenomenon in which specific letters or numbers elicit particular colors. To elucidate this mechanism, we conducted event-related potentials (ERP) and standardized low resolution brain electromagnetic tomography analysis (sLORETA) to examine the time course and localization of brain activity using color congruity task with six synesthetes and carefully matched six nonsynesthetic controls. Our results demonstrated differences between synesthetes and controls for the early time windows (N1, P2) after stimulus onset. The results of sLORETA analyses revealed a stronger activation for synesthetes vs. nonsynesthetic controls in the right temporal and occipital regions included fusiform and angular gyrus. These results suggested that the synesthetic perceptions are automatic and fast processes showing simultaneous activation of number and color processing areas.
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