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Christopher W. Tyler; Enhanced concepts of occipital retinotopy. Journal of Vision 2005;5(8):896. doi: 10.1167/5.8.896.
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© ARVO (1962-2015); The Authors (2016-present)
Rationale. Retinotopic mapping is a key property of organization of occipital cortex, predominantly on the medial surface but increasingly being identified in lateral and ventral regions. The organization of retinotopic activation these extended regions remains to be fully resolved.
Methods. Rotating wedge and logarithmic expanding ring stimuli were used with functional magnetic resonance imaging (fMRI), cortical segmentation and cut-free flattening to define a full array of retinotopic activation maps.
Results. In the dorsal occipital regions, we confirm the general agreement that there is a retinotopic V3B map lateral to V3A, and that beyond them lies a further map, V7. We specify for the first time the eccentricity mapping for V3B as running obliquely dorsal, and for V7 as running roughly parallel to the meridional mapping, offering a formal account of the paradox of co-oriented meridional and eccentricity mapping. In ventral occipital cortex, we support the view that V4 maps the full hemifield but with a shorter eccentricity span than the adjacent V3v map, and show the existence of two more maps in each hemisphere, a ventromedial occipital (VMO) map of the upper quadrant, emphasizing the upper vertical meridian, and an adjacent map with a dominant foveal representation. In lateral cortex, a dorsolateral occipital (DLO) map lies between the motion area and V3B, representing the lower quadrant with an emphasis on the lower vertical meridian, may be a counterpart to the ventromedial map This retinotopic DLO map occupies most of the territory designated as V4d on topological considerations.
Conclusion. Several retinotopic maps may be identified beyond area V4 but they have unconventional mapping properties. This new scheme offers a novel resolution to the issue of the V4 homology with monkey, by moving the ventral/dorsal split up to the next higher mapping in human occipital cortex.
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