Oriented Axon Projections in Primary Visual Cortex of the Monkey

Abstract

One important aspect of the functional architecture of primary visual cortex is the circuitry that accounts for the receptive field properties of neurons. The anatomy that underlies retinotopy and ocular dominance is well known, but no anatomical structure related to orientation selectivity has been found in primates. We examined whether the arrangement of local axon systems projecting within the cortical layers might be correlated with orientation preference in New World monkeys. We found that axons in layer 3 spread out from the site of a tracer injection in an anisotropic manner and that this elongated distribution is aligned with the preferred orientation recorded at each site. Moreover, within a few degrees of the foveal representation, the majority of the axon terminals fall within or just outside of the limits of the cortical mapping of the classical receptive field. Thus local axons produce a field of monosynaptic excitation that aligns with orientation axes and reaches neurons that have receptive fields which are adjacent in visual space.

Retinotopic Axis Specificity and Selective Clustering of Feedback Projections from V2 to V1 in the Owl Monkey

“…This extent of FbkPrj is comparable with the upper range of the distance between clusters of HrzCon within V1 of New World monkeys (3.0 mm measured end to end) (Fig. 4) (see also Sincich and Blasdel, 2001). To characterize the relationship of the FbkPrj from V2 to the map of visual space in V1, we first computed the vectorial sum of preferred orientations at the area occupied by the effective tracer-uptake zone.…”

“…11D) [for similar deviations in owl and squirrel monkeys, see Allman and Kaas (1971) and Blasdel and Campbell (2001), respectively]. Within the same region, the mean ratio of magnification factors that corresponded to the vertical and horizontal domains obtained from the two monkeys was 1.15, comparable with the value of 1.1 reported in New World monkeys (Blasdel and Campbell, 2001;Sincich and Blasdel, 2001). This ratio implies almost isotropic mapping of the visual space, as illustrated in Figure 11D.…”

“…The HrzCon are spatially organized in a nonrandom way in relation to the retinotopic map in V1 of the tree shrew (Fitzpatrick, 1996;Bosking et al, 1997), the cat (Schmidt et al, 1997), and the squirrel monkey (Sincich and Blasdel, 2001). In these species, labeled axons extend farther along an axis that corresponds to the preferred orientation at the injection site.…”

Delay effects in the human sensory system during balancing

“…This means, for example, that the green region sensitive to vertical orientation tends to be stimulated by horizontal velocity (see Weliky et al 1995or Sincich & Blasdel 2001. Consequently, the most important part of a complex image we see during balancing is not only the inclination of a vertical straight line relative to our body; our visual system also detects its angular velocity.…”

How long range is contour integration in human color vision?

“…It has been proposed (Field et al, 1993;Kovacs, 1996;Polat, 1999) that this spatial linking is mediated by long-range horizontal connections in the primate striate cortex (V1) that link distant neurons with similar orientation properties and form nonclassical receptive fields (Mitchison & Crick, 1982;Rockland & Lund, 1983;Ts'o & Gilbert, 1988;Malach et al, 1993;Kapadia et al, 1995;Zipser et al, 1996;Sincich & Blasdel, 2001). However, it is not yet known to what extent these long-range connections are limiting contour integration, and how their facilitatory effect is modulated by chromaticity, spatial frequency, or other visual attributes.…”