Topographic Organization in and near Human Visual Area V4

Abstract

The existence and location of a human counterpart of macaque visual area V4 are disputed. To resolve this issue, we used functional magnetic resonance imaging to obtain topographic maps from human subjects, using visual stimuli and tasks designed to maximize accuracy of topographic maps of the fovea and parafovea and to measure the effects of attention on topographic maps. We identified multiple topographic transitions, each clearly visible in Ն75% of the maps, that we interpret as boundaries of distinct cortical regions. We call two of these regions dorsal V4 and ventral V4 (together comprising human area V4) because they share several defining characteristics with the macaque regions V4d and V4v (which together comprise macaque area V4). Ventral V4 is adjacent to V3v, and dorsal V4 is adjacent to parafoveal V3d. Ventral V4 and dorsal V4 meet in the foveal confluence shared by V1, V2, and V3. Ventral V4 and dorsal V4 represent complementary regions of the visual field, because ventral V4 represents the upper field and a subregion of the lower field, whereas dorsal V4 represents lower-field locations that are not represented by ventral V4. Finally, attentional modulation of spatial tuning is similar across dorsal and ventral V4, but attention has a smaller effect in V3d and V3v and a larger effect in a neighboring lateral occipital region.

The Retinotopic Organization of the Human Middle Temporal Area MT/V5 and Its Cortical Neighbors

“…These retinotopic data are consistent with the view that, in humans, LO1-2 and hV4, respectively, occupy the positions of V4d and V4v in the monkey (Larsson and Heeger, 2006;Wandell et al, 2007). There is disagreement, however, about the exact organization in this region of cortex (Hansen et al, 2007). In addition, although we adhere to the definition provided by Larsson and Heeger (2006) for LO1 and LO2, these areas might be affected by the modification of the retinotopic organization we proposed for the V3A complex (Georgieva et al, 2009), restoring V3A to the location described by Tootell et al (1997).…”

“…This fits with the large ipsilateral representation found in monkey MSTd . Similarly, Hansen et al (2007) were unable to resolve the LO regions and the MT/V5 cluster because they used a coarse wedge. The present study indicates that RFs are smaller in hV4 than in the LO areas, explaining why hV4, but not LO1/2, was resolved by Hansen et al (2007).…”

“…Similarly, Hansen et al (2007) were unable to resolve the LO regions and the MT/V5 cluster because they used a coarse wedge. The present study indicates that RFs are smaller in hV4 than in the LO areas, explaining why hV4, but not LO1/2, was resolved by Hansen et al (2007). Indeed, all three studies reporting the two LO regions (Larsson and Heeger, 2006;Amano et al, 2009; present study) used a 45°wedge.…”

Visual Field Map Organization in Human Visual Cortex

“…Our findings regarding hV4 and its neighbors have since been supported by measurements from several independent studies [28,29,39,[55][56][57][58]. Hansen et al [57] initially continued the search for a hV4 organization more homologous to the split-hemifield of macaque V4 by proposing that a small section of dorsal lateral occipitotemporal cortex represented the inferior vertical meridian of hV4.…”

“…Hansen et al [57] initially continued the search for a hV4 organization more homologous to the split-hemifield of macaque V4 by proposing that a small section of dorsal lateral occipitotemporal cortex represented the inferior vertical meridian of hV4. This organization then left an hV4 division on the ventral surface that represented the full upper visual quarterfield adjacent to V3v plus some additional part of the visual field into the lower visual quarterfield.…”