title: Target sites for transcallosal fibers in human visual cortex - A combined diffusion and polarized light imaging study.
abstract: Transcallosal fibers of the visual system have preferential target sites within the occipital cortex of monkeys. These target sites coincide with vertical meridian representations of the visual field at borders of retinotopically defined visual areas. The existence of preferential target sites of transcallosal fibers in the human brain at the borders of early visual areas was claimed, but controversially discussed. Hence, we studied the distribution of transcallosal fibers in human visual cortex, searching for an organizational principle across early and higher visual areas. In-vivo high angular resolution diffusion imaging data of 28 subjects were used for probabilistic fiber tracking using a constrained spherical deconvolution approach. The fiber architecture within the target sites was analyzed at microscopic resolution using 3D polarized light imaging in a post-mortem human hemisphere. Fibers through a seed in the splenium of the corpus callosum reached the occipital cortex via the forceps major and the tapetum. We found target sites of these transcallosal fibers at borders of cytoarchitectonically defined occipital areas not only between early visual areas V1 and V2, V3d and V3A, and V3v and V4, but also between higher extrastriate areas, namely V4 (ventral) and posterior fusiform area FG1 as well as posterior fusiform area FG2 and lateral occipital cortex. In early visual areas, the target sites coincided with the vertical meridian representations of retinotopic maps. The spatial arrangement of the fibers in the 'border tuft' region at the V1/V2 border was found to be more complex than previously observed in myeloarchitectonic studies. In higher visual areas, our results provided additional evidence for a hemi-field representation in human area V4. The fiber topography in posterior fusiform gyrus indicated that additional retinotopic areas might exist, located between the recently identified retinotopic representations phPITv/phPITd and PHC-1/PHC-2 in lateral occipital cortex and parahippocampal gyrus.
authors.affiliation: Institute of Neuroscience and Medicine (INM-1), Research Centre Jülich, Jülich, Germany. Electronic address: s.caspers@fz-juelich.de.
authors.forename: Svenja
authors.initials: S
authors.lastname: Caspers
authors.affiliation: Institute of Neuroscience and Medicine (INM-1), Research Centre Jülich, Jülich, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Axer
authors.affiliation: Department of Diagnostic and Interventional Radiology, Medical Faculty, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany.
authors.forename: Julian
authors.initials: J
authors.lastname: Caspers
authors.affiliation: Institute of Neuroscience and Medicine (INM-1), Research Centre Jülich, Jülich, Germany.
authors.forename: Christiane
authors.initials: C
authors.lastname: Jockwitz
authors.affiliation: Institute of Neuroscience and Medicine (INM-1), Research Centre Jülich, Jülich, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Jütten
authors.affiliation: Institute of Neuroscience and Medicine (INM-1), Research Centre Jülich, Jülich, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Reckfort
authors.affiliation: Institute of Neuroscience and Medicine (INM-1), Research Centre Jülich, Jülich, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Grässel
authors.affiliation: Institute of Neuroscience and Medicine (INM-1), Research Centre Jülich, Jülich, Germany; C. and O. Vogt Institute for Brain Research, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany; JARA-BRAIN, Jülich-Aachen Research Alliance, Jülich, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Amunts
authors.affiliation: Institute of Neuroscience and Medicine (INM-1), Research Centre Jülich, Jülich, Germany; JARA-BRAIN, Jülich-Aachen Research Alliance, Jülich, Germany; Department of Psychiatry, Psychotherapy, and Psychosomatics, RWTH Aachen University, Aachen, Germany.
authors.forename: Karl
authors.initials: K
authors.lastname: Zilles
mesh_terms: D001931:Brain Mapping; D003337:Corpus Callosum / Q000502:physiology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D014793:Visual Cortex / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology*
keywords: Cortical fiber architecture; Diffusion imaging; Fiber tracking; HARDI; Occipital cortex; PLI; Polarized light imaging; Visual system; White-matter tractography