Cytochrome Oxidase Stripes In V2 Research Articles

Two Projection Streams from Macaque V1 to the Pale Cytochrome Oxidase Stripes of V2

In the primate visual cortex, areas V1 and V2 distribute information they receive from the retina to virtually all extrastriate cortex, parsing this information into dorsal and ventral streams. Therefore, understanding the connectivity between V1 and V2 is crucial to understand visual cortical processing. Cytochrome oxidase staining in V2 reveals a repeating pattern of pale-thick-pale-thin stripes. V1 sends parallel output pathways to distinct V2 stripes. Previous models proposed either three or two parallel V1-to-V2 pathways in macaque, but both models viewed the two pale stripes within a single stripe cycle as a single compartment. However, recent studies have suggested that the two pale stripes may be functionally distinct, and in marmosets they also differ anatomically in the laminar origin of projections they receive from V1. Here we have asked whether the two pale stripes are also anatomically distinct in macaque. We made small retrograde tracer injections in different pale stripe types. We found that while both pale stripes receive a predominant V1 input from layers 2/3, only one set of pale stripes (pale lateral) receives significant projections from layer 4B, while the other set (pale medial) receives few or no layer 4B projections. Moreover, different tracer injections in nearby pale stripe types revealed that 97-99% of layer 2/3 cells only project to a single pale stripe type. These results demonstrate that in macaque, the two pale stripes are anatomically distinct compartments, and support the notion of two distinct projection streams from V1 to the two pale stripes of V2.

Cortical and subcortical connections of V1 and V2 in early postnatal macaque monkeys

Connections of primary (V1) and secondary (V2) visual areas were revealed in macaque monkeys ranging in age from 2 to 16 weeks by injecting small amounts of cholera toxin subunit B (CTB). Cortex was flattened and cut parallel to the surface to reveal injection sites, patterns of labeled cells, and patterns of cytochrome oxidase (CO) staining. Projections from the lateral geniculate nucleus and pulvinar to V1 were present at 4 weeks of age, as were pulvinar projections to thin and thick CO stripes in V2. Injections into V1 in 4- and 8-week-old monkeys labeled neurons in V2, V3, middle temporal area (MT), and dorsolateral area (DL)/V4. Within V1 and V2, labeled neurons were densely distributed around the injection sites, but formed patches at distances away from injection sites. Injections into V2 labeled neurons in V1, V3, DL/V4, and MT of monkeys 2-, 4-, and 8-weeks of age. Injections in thin stripes of V2 preferentially labeled neurons in other V2 thin stripes and neurons in the CO blob regions of V1. A likely thick stripe injection in V2 at 4 weeks of age labeled neurons around blobs. Most labeled neurons in V1 were in superficial cortical layers after V2 injections, and in deep layers of other areas. Although these features of adult V1 and V2 connectivity were in place as early as 2 postnatal weeks, labeled cells in V1 and V2 became more restricted to preferred CO compartments after 2 weeks of age.

Four Projection Streams from Primate V1 to the Cytochrome Oxidase Stripes of V2

In the primate visual system, areas V1 and V2 distribute information they receive from the retina to all higher cortical areas, sorting this information into dorsal and ventral streams. Therefore, knowledge of the organization of projections between V1 and V2 is crucial to understand how the cortex processes visual information. In primates, parallel output pathways from V1 project to distinct V2 stripes. The traditional tripartite division of V1-to-V2 projections was recently replaced by a bipartite scheme, in which thin stripes receive V1 inputs from blob columns, and thick and pale stripes receive common input from interblob columns. Here, we demonstrate that thick and pale stripes, instead, receive spatially segregated V1 inputs and that the interblob is partitioned into two compartments: the middle of the interblob projecting to pale stripes and the blob/interblob border region projecting to thick stripes. Double-labeling experiments further demonstrate that V1 cells project to either thick or pale stripes, but rarely to both. We also find laminar specialization of V1 outputs, with layer 4B contributing projections mainly to thick stripes, and no projections to one set of pale stripes. These laminar differences suggest different contribution of magno, parvo, and konio inputs to each V1 output pathway. These results provide a new foundation for parallel processing models of the visual system by demonstrating four V1-to-V2 pathways: blob columns-to-thin stripes, blob/interblob border columns-to-thick stripes, interblob columns-to-pale(lateral) stripes, layer 2/3-4A interblobs-to-pale(medial) stripes.

A hierarchy of the functional organization for color, form and disparity in primate visual area V2

By combining optical imaging, single unit electrophysiology and cytochrome oxidase (CO) histology, we sought to reveal in greater detail the functional organization within the CO stripes of visual area V2 of primates. To visualize the disparity selective regions of V2, the imaging of binocular interaction was employed. These imaging maps guided single unit penetrations that then revealed a columnar organization for disparity. Our studies also showed a pattern of intermixing between the color and disparity pathways of V2, including the existence of single cells tuned for both color and disparity. While previous studies have suggested that the CO stripes of V2 constitute the fundamental organizational unit within V2, our results show a further level of organization consisting of functionally distinct subcompartments, 0.7–1.5 mm in diameter, within individual stripes. These subcompartments, which are not clearly revealed by CO histochemistry, lie within each of the thin, pale, and thick CO dense stripes in V2 and are specific for aspects of color, orientation and retinal disparity, respectively. The present results favor an architectural view of V2, not unlike that of V1, as a collection of functionally distinct subcompartments or modules situated within each of the V2 stripes. These modules also support the notion that for each cortical area (e.g. V1, V2, V4), there exists a stereotyped cortical module with a geometry that is characteristic for each area. These modules exist as a middle tier in a hierarchy of functional organization within V2.

The second visual area in the marmoset monkey: visuotopic organisation, magnification factors, architectonical boundaries, and modularity.

The organisation of the second visual area (V2) in marmoset monkeys was studied by means of extracellular recordings of responses to visual stimulation and examination of myelin- and cytochrome oxidase-stained sections. Area V2 forms a continuous cortical belt of variable width (1-2 mm adjacent to the foveal representation of V1, and 3-3.5 mm near the midline and on the tentorial surface) bordering V1 on the lateral, dorsal, medial, and tentorial surfaces of the occipital lobe. The total surface area of V2 is approximately 100 mm2, or about 50% of the surface area of V1 in the same individuals. In each hemisphere, the receptive fields of V2 neurones cover the entire contralateral visual hemifield, forming an ordered visuotopic representation. As in other simians, the dorsal and ventral halves of V2 represent the lower and upper contralateral quadrants, respectively, with little invasion of the ipsilateral hemifield. The representation of the vertical meridian forms the caudal border of V2, with V1, whereas a field discontinuity approximately coincident with the horizontal meridian forms the rostral border of V2, with other visually responsive areas. The bridge of cortex connecting dorsal and ventral V2 contains neurones with receptive fields centred within 1 degree of the centre of the fovea. The visuotopy, size, shape and location of V2 show little variation among individuals. Analysis of cortical magnification factor (CMF) revealed that the V2 map of the visual field is highly anisotropic: for any given eccentricity, the CMF is approximately twice as large in the dimension parallel to the V1/V2 border as it is perpendicular to this border. Moreover, comparison of V2 and V1 in the same individuals demonstrated that the representation of the central visual field is emphasised in V2, relative to V1. Approximately half of the surface area of V2 is dedicated to the representation of the central 5 degrees of the visual field. Calculations based on the CMF, receptive field scatter, and receptive field size revealed that the point-image size measured parallel to the V1/V2 border (2-3 mm) equals the width of a full cycle of cytochrome oxidase stripes in V2, suggesting a close correspondence between physiological and anatomical estimates of the dimensions of modular components in this area.

The global pattern of cytochrome oxidase stripes in visual area V2 of the macaque monkey.

In primate visual area V2, histochemical staining for cytochrome oxidase (CO) reveals a tripartite pattern of densely labeled thick and thin stripes separated by pale interstripes. This modularity is believed to be related to functionally distinct processing streams that course through the hierarchy of visual areas. Here, we studied the overall pattern of CO stripes in V2 of the macaque monkey, using tissue that had been physically unfolded and flattened prior to histological sectioning. CO stripes were identified on the basis of their physical dimensions and on their differential immunoreactivity for the monoclonal antibody Cat-301. We observed several distinctive features of compartmental organization in V2. The most prominent was a dorso-ventral asymmetry in the stripe pattern, occurring in the majority of cases studied. In dorsal V2, most stripes measure approximately 10 mm in length and run roughly orthogonal to both the posterior and anterior borders of V2. In contrast, many stripes in ventral V2 have a curved or oblique trajectory, and some extend up to 20 mm in length. Stripes following a curved trajectory often become nearly parallel to the anterior border of V2. These differences imply an asymmetry in how the visual field maps onto dorsal versus ventral stripes. Occasionally, thin stripes fail to alternate with thick stripes but instead occur next to one other, separated only by interstripes. In three most complete reconstructions, we found that unfolded V2 is approximately 110 mm in length, approximately 900 mm2 in surface area, and that it contains approximately 28 complete sets of stripes (one thick, one thin and two interstripes), yielding an average of approximately 4 mm per set of stripes. The maximum width of ventral V2 (13-14 mm) exceeds that of dorsal V2 (10 mm), and there is a consistent narrowing of V2 in the region of foveal representation (3-5 mm).