Fig. 1
From: Top-down feedback controls spatial summation and response amplitude in primate visual cortex
Optogenetic inactivation of V2 feedback terminals: experimental design and ArchT-GFP expression in V2 feedback terminals. a Schematics of the marmoset brain. Red box: approximate location of the optically imaged region in b. Black box: V1 and V2 region shown enlarged in c. b Optical imaging identifies V1/V2 border (white line). Left panel: cortical surface vasculature imaged under green light, used as reference to position pipettes for viral injections (green dots). Middle panel: orientation map generated by subtracting responses to 0° and 90° gratings (as shown in inset). V2 can be identified by larger orientation domains compared to V1. Right panel: retinotopic map generated by subtracting responses to 90° oriented gratings occupying complementary and adjacent strips (1° in width) of visual space (as shown in inset above; see Methods). The V1/V2 border can be identified by the presence of stripes in V1, running approximately parallel to the V1/V2 border, which are absent in V2 (as the grating parameters were optimized for V1, but not V2, cell; see Methods). c Schematics of the inactivation paradigm: multiple viral injections were targeted to V2, array recordings and laser photostimulation to V1. d ArchT-GFP expression in V1 and V2. Top left: sagittal section through V1 and V2, viewed under GFP fluorescence, showing two injection sites confined to V2, and resulting expression of ArchT-GFP in the axon terminals of V2 feedback neurons within V1 layers 1–3, 4B and 5/6 (typical feedback laminar termination pattern32,33). This tissue section was located near the lateralmost aspect of the hemisphere, therefore the infragranular layers are elongated due to the lateral folding-over of the cortical sheet. Solid contour: V1/V2 border. Dashed contours: laminar borders delineated on the same section counterstained with DAPI (top right). Bottom panels 1–5: higher magnification of label inside the white boxes numbered 1-5 in the top left panel. Panels 1–2 show multiple clusters of labeled somata (e.g., arrowheads) at the V2 injection sites; instead, there is only one labeled soma (arrowhead) in panel 4, and none in panels 3,5. e Top panel: GFP excitation (arrowhead) through the intact thinned skull, approximately two months after viral injection. Bottom panel: Tangential section through V1 showing the location of a DiI-coated electrode penetration (arrowhead) amid ArchT-GFP-expressing feedback axon terminals (green fluorescence)
