Variability of visual field maps in human early extrastriate cortex challenges the canonical model of organization of V2 and V3

Visual field maps in human early extrastriate areas (V2 and V3) are traditionally thought to form mirror-image representations which surround the primary visual cortex (V1). According to this scheme, V2 and V3 form nearly symmetrical halves with respect to the calcarine sulcus, with the dorsal halves representing the lower contralateral quadrants, and the ventral halves representing the upper contra lateral quadrants. This arrangement is considered to be consistent across individuals, and thus predictable with reasonable accuracy using templates. However, data that deviate from this expected pattern have been observed, but mainly treated as artifactual. Here we systematically investigate individual variability in the visual field maps of human early visual cortex using the large-scale 7T Human Connectome Project (HCP) retinotopy dataset. Our results demonstrate substantial and principled inter-individual variability in early visual retinotopy. Visual field representation in the dorsal portions of V2 and V3 were more variable than their ventral counterparts, including substantial departures from the expected mirror-symmetrical patterns. Surprisingly, only one-third of individuals had maps that conformed to the expected pattern. In addition, retinotopic maps in the left hemisphere were more variable than those in the right hemisphere. Our findings challenge the current view that interindividual variability in early extrastriate cortex is negligible, and that the dorsal portions of V2 and V3 are roughly mirror images of their ventral counterparts.