Intrinsic connections of macaque striate cortex: axonal projections of cells outside lamina 4C

Abstract

We have exploited a technique for making small injections of horseradish peroxidase into single cortical laminae in order to study axonal projections in macaque striate cortex. In the preceding paper (Fitzpatrick, D., J. S. Lund, and G. G. Blasdel (1985) J. Neurosci. 5: 3329-3349) we examined the projections of cells in lamina 4C--cells that receive most of their input from the lateral geniculate nucleus. The present paper deals with the projections of neurons that lie outside of lamina 4C. Among our findings are several projections that previously had not been described in the monkey. These include: a strong and precise (point-to-point) projection from lamina 4B to lamina 2/3A, a reciprocal projection from 2/3A back to 4B, a definite projection from lamina 4B to 5B, as well as a prominent input to lamina 6 from 5B. In many cases, we find it possible to trace the flow of visual information through several "circuits" in striate cortex that have, as their output, projections to extrastriate cortex or to the brainstem. Our results offer additional insights in this regard since we are able, in many cases, to compare the lateral spreads of particular projections. These vary and can be separated into at least three categories: those that terminate in a precise, point-to-point, fashion, those that spread widely, and those that terminate in a laterally periodic fashion. In several cases we find evidence for a correlation between specific patterns of projection and known physiological differences between the topographies of laminae that are connected. In cases where two laminae possess similar topographies (for example, where both contain orderly maps for orientation) their interconnections appear precise, with little diffuse spread. In cases where two laminae are characterized by strikingly different topographies (where, for example, one contains an orderly map for orientation and the other a precise map for retinotopic position, but no specificity for orientation), the connections appear more diffuse.

Horizontal projections of area 17 in Cebus monkeys: metric features, and modular and laminar distribution

“…In the latter case the possibility of uptake of biocytin by passing fibers remains open. Against this possibility is the fact that similar patterns of labeling are obtained irrespective of the amount of tissue damaged (8,16,31, and the present results). The first hypothesis, i.e., the same cells projecting both intrinsically and extrinsically, is supported by the results obtained after isolated injections into layers II and III or IVb (31) which show retrogradely labeled pyramidal cells and axon terminals forming patches in layers II and III.…”

“…The present paper described retrogradely (31), these projections were asymmetrical in relation to the injection site, with strong labeling on one side as compared to the other. In cases of iontophoretic injections located in layers II and III the infragranular labeled cells were found in layer V, similar to the results reported by Livingstone and Hubel (14).…”

Intrinsic connections of macaque striate cortex: afferent and efferent connections of lamina 4C

“…The laminar numbering system used in this and the following paper (Blasdel et al, 1985) is shown in Figure 1. Since certain laminar borders do not appear sharp in Nissl-stained sections, we have used the distribution of cytochrome oxidase activity, as well as cytoarchitecture, to define laminar borders (see Blasdel and Fitzpatrick, 1984, for further discussion).…”

“…In the following paper (Blasdel et al, 1985) we examine the interconnections of the remaining layers which constitute the source of projections to the thalamus, brainstem and to extrastriate cortex. Some of these results have been reported briefly (Blasdel et al, 1983;).…”

A neural network model of attention-modulated neurodynamics

“…Top-down inter-areal connections terminate in the supra-(layer 2/3) and infra-granular layers (layer 5/6). Using techniques of microinjections of D-3H-Asp and injections of horseradish peroxidase, very detailed intra-areal connections, including intra-laminar and lateral excitatory projections have been experimentally investigated Blasdel et al 1985 andKisvarday et al 1989).…”