Grapheme-color and tone-color synesthesia is associated with structural brain changes in visual regions implicated in color, form, and motion

Abstract

Synesthesia is a rare condition in which stimulation in one modality leads to a secondary experience in another sensory modality. Varying accounts attribute the condition to either neuroanatomical differences between the synesthetes and non-synesthetes or functional differences in how sensory brain regions interact. This study employed voxel-based morphometry to examine whether synesthetes who experience both grapheme-color and tone-color synesthesia as their evoked sensation show neuroanatomical differences in gray matter volume compared to non-synesthetes. We observed that synesthetes showed an increase in gray matter volume in left posterior fusiform gyrus (FG), but a concomitant decrease in anterior regions of left FG and left MT/V5. These findings imply that synesthesia for color is linked to neuroanatomical changes between adjacent regions of the visual system.

Keywords:

• Synesthesia
• Voxel-based morphometry
• Color
• Motion
• Vision

Acknowledgments

M.J.B. is supported by a British Academy Postdoctoral Fellowship. R.K. is supported by the Human Frontier Science Program and Japan Society for the Promotion of Science. This work was partly supported by an Economic and Social Research Council grant to M.J.B.