BRAIN REGIONS. “Several groups have demonstrated that simple achromatic graphemes activate both grapheme regions as well as color area V4 (a region of visual cortex that shows a stronger response to colors than to grayscale stimuli) in the brains of synesthetes, which is consistent with the view that synesthetic colors are sensory in nature (i.e., arise through a bottom-up processing stream), as opposed to being high-level cognitive associations, as has been proposed.”
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