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Danielle Reitsma, Mary Jo Maciejewski, Viktor Szeder, Douglas Ward, John Ul, John Ulmer, Wade Mueller, Bernd Remler, Edgar DeYoe; Apparent retinotopic reorganization in human visual cortex with central pathology. Journal of Vision 2011;11(15):10. doi: https://doi.org/10.1167/11.15.10.
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© ARVO (1962-2015); The Authors (2016-present)
The potential for reorganization of human cortex in response to central pathology remains controversial, particularly for visual cortex. Consequently, we used BOLD fMRI and conventional visual field mapping techniques (checkered rings and wedges) to study cortical organization in healthy subjects and a group of 30 patients with central pathology. To dissociate reorganization from pathology-related deletions, we focused our analysis on increases in representation, specifically, of the ipsilateral visual field in each hemisphere. Patient hemispheres were divided into two distinct groups: (1) Not reorganized (n = 54) - Retinotopic maps within these hemispheres could have pathology-related deletions but the remaining topography was normal. (2) Reorganized (n = 3) - These hemispheres all had increased representation of the ipsilateral field beyond the range of normal subjects, despite pathology-related loss in other portions of the field. Quantitative analysis revealed that the number of fMRI voxels representing the ipsilateral hemifield in reorganized hemispheres averaged over 3× the number in healthy subjects (p = 0.005) and 7× the number in patient hemispheres without reorganization (p < 0.002). A concern was that patients with scotomata can develop an eccentric preferred retinal locus (PRL) for fixation that might produce artifactual changes in retinotopy. To control for this, we used scanning laser opthalmoscopy with optical coherence tomography to measure the average preferred fixation locus relative to the foveal pit in 2 of the 3 patients with reorganization and found offsets of less than 1° in both. We then estimated the worst-case effect of a 1° PRL on cortical retinotopy both empirically using BOLD-fMRI in healthy subjects with intentionally shifted fixation and, theoretically, using a computational model (based on Schira et al., 2009). Neither the empirically nor theoretically shifted fixation yielded cortical retinotopy that could account for the reorganization observed in the patients. Thus, we conclude that cortical retinotopy in patients with central visual pathology can undergo apparent reorganization so as to increase the ipsilateral field representation, and that this effect is not accounted for by a PRL.
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