| Two different parcellations of visual cortex anterior to dorsal V2 (V2d) in marmosets have been proposed. In one, dorsal V3 (V3d), representing the lower visual field (LVF), is situated between V2d and DM (representing both upper visual field, UVF, and LVF, i.e., DM+ and DM-, respectively). In the other, two areas, DM and VLP, border V2d anteriorly. To determine which proposal is correct, I asked: (1) does DM+ abut V2d? (2) how many areas abut V2d?;A confound to these studies is that LVF-representing regions near HMRs could make connections with UVF-representing cortex to maintain retinotopic continuity across the discontinuous HMR. Therefore, the existence of such connections were examined. V2 cells located within ∼1 mm of the HMR were found to indeed make such connections, which, unlike those of DM+, are consistently located near HMRs.;The second question was addressed by making mediolateral injection sequences in cortex anterior to V2d, and examining the laminar and areal patterns of resulting label. Two areas directly abutting V2d were found, each having unique connectivity patterns.;These results are consistent with an UVF representation (DM+), and two areas (DM+ and VLP) directly abutting V2d anteriorly.;The first question was addressed by delivering seven different tracer injections in anteroposterior sequences, spanning the width of V2d from its vertical to its horizontal meridian representations (VMR and HMR, respectively), or extending from the V2d HMR to cortex anterior to V2d. The distance of the posterior DM+ border from the V1/V2 border was first determined based on: (1) the V1 laminar pattern of cell label resulting from injections in DM vs. V2, and (2) label in UVF- representing regions produced by injections in DM+ but not in LVF-representing cortex (e.g., V2d or V3d). I then examined whether injection sequences spanning the width of V2 produced a mirror-image sequence of label caudal to the DM+ posterior border, i.e., in V3d, or rostral to it, i.e., in DM-. The DM+ posterior border was 3.5-4 9 mm anterior to the V1/V2 border; the mirror-image label sequence lay anterior to this distance, indicating that there is no V3d between V2d and DM+. |
