title: White matter microstructure throughout the brain correlates with visual imagery in grapheme-color synesthesia.
abstract: In this study we show, for the first time, a correlation between the neuroanatomy of the synesthetic brain and a metric that measures behavior not exclusive to the synesthetic experience. Grapheme-color synesthetes (n=20), who experience colors triggered by viewing or thinking of specific letters or numbers, showed altered white matter microstructure, as measured using diffusion tensor imaging, compared with carefully matched non-synesthetic controls. Synesthetes had lower fractional anisotropy and higher perpendicular diffusivity when compared to non-synesthetic controls. An analysis of the mode of anisotropy suggested that these differences were likely due to the presence of more crossing pathways in the brains of synesthetes. Additionally, these differences in white matter microstructure correlated negatively, and only for synesthetes, with a measure of the vividness of their visual imagery. Synesthetes who reported the most vivid visual imagery had the lowest fractional anisotropy and highest perpendicular diffusivity. We conclude that synesthetes as a population vary along a continuum while showing categorical differences in neuroanatomy and behavior compared to non-synesthetes.
authors.affiliation: Department of Psychiatry, University of Cambridge, Cambridge CB2 0SZ, UK. Electronic address: kw401@cam.ac.uk.
authors.forename: Kirstie J
authors.initials: KJ
authors.lastname: Whitaker
authors.affiliation: Department of Neurology, University of California, Davis 4860 Y St., Suite 3700, Sacramento, CA 95817, USA.
authors.forename: Xiaojian
authors.initials: X
authors.lastname: Kang
authors.affiliation: Medical Research Service, Veterans Administration, Martinez, CA 94553, USA.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Herron
authors.affiliation: Department of Neurology, University of California, Davis 4860 Y St., Suite 3700, Sacramento, CA 95817, USA; Medical Research Service, Veterans Administration, Martinez, CA 94553, USA; Center for Neurosciences, University of California, Davis, 1544 Newton Ct., Davis, CA 95616, USA; Center for Mind and Brain, University of California, Davis, 202 Cousteau Place, Suite 201, Davis, CA 95616, USA.
authors.forename: David L
authors.initials: DL
authors.lastname: Woods
authors.affiliation: Medical Research Service, Veterans Administration, Martinez, CA 94553, USA; Cognitive Neuropsychology Laboratory, University of California, Berkeley, CA 94720-5050, USA.
authors.forename: Lynn C
authors.initials: LC
authors.lastname: Robertson
authors.affiliation: Cognitive Neuropsychology Laboratory, University of California, Berkeley, CA 94720-5050, USA.
authors.forename: Bryan D
authors.initials: BD
authors.lastname: Alvarez
mesh_terms: D000328:Adult; D016880:Anisotropy; D001921:Brain / Q000473:pathology*; D001931:Brain Mapping; D003118:Color Perception / Q000502:physiology; D056324:Diffusion Tensor Imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007092:Imagination / Q000502:physiology*; D008297:Male; D009413:Nerve Fibers, Myelinated / Q000473:pathology*; D010468:Perceptual Disorders / Q000473:pathology*; D000080311:Synesthesia; D055815:Young Adult