title: Hemifield columns co-opt ocular dominance column structure in human achiasma.
abstract: In the absence of an optic chiasm, visual input to the right eye is represented in primary visual cortex (V1) in the right hemisphere, while visual input to the left eye activates V1 in the left hemisphere. Retinotopic mapping In V1 reveals that in each hemisphere left and right visual hemifield representations are overlaid (Hoffmann et al., 2012). To explain how overlapping hemifield representations in V1 do not impair vision, we tested the hypothesis that visual projections from nasal and temporal retina create interdigitated left and right visual hemifield representations in V1, similar to the ocular dominance columns observed in neurotypical subjects (Victor et al., 2000). We used high-resolution fMRI at 7T to measure the spatial distribution of responses to left- and right-hemifield stimulation in one achiasmic subject. T2-weighted 2D Spin Echo images were acquired at 0.8mm isotropic resolution. The left eye was occluded. To the right eye, a presentation of flickering checkerboards alternated between the left and right visual fields in a blocked stimulus design. The participant performed a demanding orientation-discrimination task at fixation. A general linear model was used to estimate the preference of voxels in V1 to left- and right-hemifield stimulation. The spatial distribution of voxels with significant preference for each hemifield showed interdigitated clusters which densely packed V1 in the right hemisphere. The spatial distribution of hemifield-preference voxels in the achiasmic subject was stable between two days of testing and comparable in scale to that of human ocular dominance columns. These results are the first in vivo evidence showing that visual hemifield representations interdigitate in achiasmic V1 following a similar developmental course to that of ocular dominance columns in V1 with intact optic chiasm.
authors.affiliation: Department of Psychology, University of Minnesota, Minneapolis, MN, United States.
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: Olman
authors.affiliation: Department of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, United States.
authors.forename: Pinglei
authors.initials: P
authors.lastname: Bao
authors.affiliation: Department of Psychology, University of Minnesota, Minneapolis, MN, United States.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Engel
authors.affiliation: Department of Neuroscience, University of Minnesota, Minneapolis, MN, United States.
authors.forename: Andrea N
authors.initials: AN
authors.lastname: Grant
authors.affiliation: University of California, Berkeley, Berkeley, CA, United States.
authors.forename: Chris
authors.initials: C
authors.lastname: Purington
authors.affiliation: Schepens Eye Research Institute, Harvard Medical School, Boston, MA, United States.
authors.forename: Cheng
authors.initials: C
authors.lastname: Qiu
authors.affiliation: Department of Psychology, University of Washington, Seattle, WA, United States.
authors.forename: Michael-Paul
authors.initials: MP
authors.lastname: Schallmo
authors.affiliation: Department of Psychology, University of Southern California, Los Angeles, CA, United States.
authors.forename: Bosco S
authors.initials: BS
authors.lastname: Tjan
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D023882:Dominance, Ocular / Q000502:physiology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D009897:Optic Chiasm / Q000002:abnormalities* / Q000000981:diagnostic imaging*; D014793:Visual Cortex / Q000000981:diagnostic imaging*